U.S. patent application number 16/143167 was filed with the patent office on 2019-01-24 for epoxy-based resin system composition containing a latent functionality for polymer adhesion improvement to prevent sulfur related corrosion.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to Dylan J. Boday, Joseph Kuczynski, Jason T. Wertz, Jing Zhang.
Application Number | 20190027281 16/143167 |
Document ID | / |
Family ID | 59226645 |
Filed Date | 2019-01-24 |
United States Patent
Application |
20190027281 |
Kind Code |
A1 |
Boday; Dylan J. ; et
al. |
January 24, 2019 |
EPOXY-BASED RESIN SYSTEM COMPOSITION CONTAINING A LATENT
FUNCTIONALITY FOR POLYMER ADHESION IMPROVEMENT TO PREVENT SULFUR
RELATED CORROSION
Abstract
An epoxy-based resin system composition includes a latent
functionality for polymer adhesion improvement. The composition may
be used to produce an overcoat layer and/or protection layer in an
anti-sulfur resistor (ASR). In some embodiments, the composition
include epoxy-based resin(s), hardener(s) and, optionally, blowing
agent(s) and/or filler(s). An epoxide functionality of one or more
of the epoxy-based resin(s) and a reactive functionality of one or
more of the hardener(s) react with each other at a first
temperature. The latent functionality, which does not react at the
first temperature, is contained in at least one of the epoxy-based
resin(s), hardener(s) and filler(s) and reacts in response to
another stimulus (e.g., UV light/initiator and/or a second
temperature greater than the first temperature) to enhance chemical
bonding. Optionally, voids created via etching and/or the blowing
agent(s) may be used to enhance mechanical bonding, alone, or in
combination with filler(s) exposed in the voids.
Inventors: |
Boday; Dylan J.; (Tucson,
AZ) ; Kuczynski; Joseph; (North Port, FL) ;
Wertz; Jason T.; (Pleasant Valley, NY) ; Zhang;
Jing; (Poughkeepsie, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
Armonk |
NY |
US |
|
|
Family ID: |
59226645 |
Appl. No.: |
16/143167 |
Filed: |
September 26, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14989446 |
Jan 6, 2016 |
10121573 |
|
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16143167 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D 163/00 20130101;
C09D 5/08 20130101; C08K 7/10 20130101; C09D 7/65 20180101; H01C
1/012 20130101; C09D 7/62 20180101; C09D 5/082 20130101; C08K 13/06
20130101; H01C 1/032 20130101; C08K 9/04 20130101; H01C 17/02
20130101; C08K 13/06 20130101; C08L 63/00 20130101; C08K 9/04
20130101; C08L 63/00 20130101 |
International
Class: |
H01C 1/032 20060101
H01C001/032; H01C 17/00 20060101 H01C017/00; H01C 1/012 20060101
H01C001/012; C09D 163/00 20060101 C09D163/00; C09D 5/08 20060101
C09D005/08; C09D 7/65 20180101 C09D007/65; C08K 13/06 20060101
C08K013/06; C08K 7/10 20060101 C08K007/10; C09D 7/62 20180101
C09D007/62 |
Claims
1. A composition, comprising: one or more epoxy-based resins,
wherein at least one of the one or more epoxy-based resins includes
a first epoxide functionality; one or more hardeners, wherein at
least one of the one or more hardeners includes a first reactive
functionality, and wherein the first reactive functionality and the
first epoxide functionality react with each other at a first
temperature; one or more filler materials, wherein a latent
functionality is contained in the one or more filler materials,
wherein the latent functionality does not react at the first
temperature, and wherein the latent functionality reacts in
response to a stimulus comprising at least one of ultraviolet (UV)
light and a second temperature greater than the first
temperature.
2. The composition as recited in claim 1, wherein the one or more
filler materials includes at least one of silica fibers and silica
particles surface modified to contain the latent functionality, and
wherein the latent functionality includes a secondary amine.
3. The composition as recited in claim 1, wherein the one or more
filler materials includes at least one of silica fibers and silica
particles surface modified to contain the latent functionality
using a silane coupling agent having two secondary amine
groups.
4. The composition as recited in claim 3, wherein the silane
coupling agent includes
vinylbenzylethylenediaminepropyltrimethoxysilane hydrochloride.
5. The composition as recited in claim 1, wherein the one or more
filler materials includes at least one of silica fibers and silica
particles surface modified to contain the latent functionality
using a silane coupling agent, and wherein the silane coupling
agent is selected from the group consisting of
vinylbenzylethylenediaminepropyltrimethoxysilane hydrochloride,
trimethoxy[3-(methyl-amino)propyl]-silane,
N-[3-(trimethoxysilyl)propyl]ethylene-diamine, and combinations
thereof.
6. The composition as recited in claim 1, wherein the one or more
filler materials includes at least one of silica fibers and silica
particles surface modified to contain the latent functionality, and
wherein the latent functionality includes a latent epoxy or
amine.
7. The composition as recited in claim 1, wherein the one or more
filler materials is selected from the group consisting of silica
fibers surface modified to contain the latent functionality, silica
particles surface modified to contain the latent functionality,
carbon black surface modified to contain the latent functionality,
TiO.sub.2 surface modified to contain the latent functionality, ZnO
surface modified to contain the latent functionality, and
combinations thereof.
8. The composition as recited in claim 1, wherein the one or more
epoxy-based resins includes N,N-Diglycidyl-4-glycidyloxyaniline,
wherein the one or more hardeners includes Methyltetrahydrophthalic
anhydride (MTHPA), and wherein the one or more filler materials
includes silica fibers surface modified to contain the latent
functionality using
vinylbenzylethylenediaminepropyltrimethoxysilane hydrochloride.
9. The composition as recited in claim 1, further comprising one or
more blowing agents, wherein the one or more blowing agents is
selected from the group consisting of ammonium carbonate, sodium
bicarbonate, sulfonyl hydrazide, azodicarbonamide (ADC) foaming
agents, p-p'-oxybis(benzenesulfonyl-hydrazide) (OBSH) foaming
agents, and combinations thereof.
10. The composition as recited in claim 1, further comprising one
or more blowing agents, wherein the one or more blowing agents is
selected from the group consisting of pentane, toluene,
fluorocarbons (FCs), chlorofluorocarbons (CFCs),
hydrochlorofluorocarbons (HCFCs), and combinations thereof.
11. A composition, comprising: one or more epoxy-based resins,
wherein at least one of the one or more epoxy-based resins includes
a first epoxide functionality; one or more hardeners, wherein at
least one of the one or more hardeners includes a first reactive
functionality, and wherein the first reactive functionality and the
first epoxide functionality react with each other at a first
temperature; one or more filler materials, wherein a latent
functionality is contained in the one or more filler materials,
wherein the latent functionality does not react at the first
temperature, and wherein the latent functionality reacts in
response to a stimulus comprising at least one of ultraviolet (UV)
light and a second temperature greater than the first temperature;
one or more blowing agents; one or more surfactants.
12. The composition as recited in claim 11, wherein the one or more
filler materials includes at least one of silica fibers and silica
particles surface modified to contain the latent functionality, and
wherein the latent functionality includes a secondary amine.
13. The composition as recited in claim 11, wherein the one or more
filler materials includes at least one of silica fibers and silica
particles surface modified to contain the latent functionality
using a silane coupling agent having two secondary amine
groups.
14. The composition as recited in claim 13, wherein the silane
coupling agent includes
vinylbenzylethylenediaminepropyltrimethoxysilane hydrochloride.
15. The composition as recited in claim 11, wherein the one or more
filler materials includes at least one of silica fibers and silica
particles surface modified to contain the latent functionality
using a silane coupling agent, and wherein the silane coupling
agent is selected from the group consisting of
vinylbenzylethylenediaminepropyltrimethoxysilane hydrochloride,
trimethoxy[3-(methyl-amino)propyl]-silane,
N-[3-(trimethoxysilyl)propyl]ethylene-diamine, and combinations
thereof.
16. The composition as recited in claim 11, wherein the one or more
filler materials includes at least one of silica fibers and silica
particles surface modified to contain the latent functionality, and
wherein the latent functionality includes a latent epoxy or
amine.
17. The composition as recited in claim 11, wherein the one or more
filler materials is selected from the group consisting of silica
fibers surface modified to contain the latent functionality, silica
particles surface modified to contain the latent functionality,
carbon black surface modified to contain the latent functionality,
TiO.sub.2 surface modified to contain the latent functionality, ZnO
surface modified to contain the latent functionality, and
combinations thereof.
18. The composition as recited in claim 11, wherein the one or more
blowing agents is selected from the group consisting of ammonium
carbonate, sodium bicarbonate, sulfonyl hydrazide, azodicarbonamide
(ADC) foaming agents, p-p'-oxybis(benzenesulfonyl-hydrazide) (OBSH)
foaming agents, and combinations thereof.
19. The composition as recited in claim 11, wherein the one or more
blowing agents is selected from the group consisting of pentane,
toluene, fluorocarbons (FCs), chlorofluorocarbons (CFCs),
hydrochlorofluorocarbons (HCFCs), and combinations thereof.
20. The composition as recited in claim 11, wherein the one or more
epoxy-based resins includes N,N-Diglycidyl-4-glycidyloxyaniline,
wherein the one or more hardeners includes Methyltetrahydrophthalic
anhydride (MTHPA), wherein the one or more filler materials
includes silica fibers surface modified to contain the latent
functionality using
vinylbenzylethylenediaminepropyltrimethoxysilane hydrochloride,
wherein the one or more blowing agents includes a
p-p'-oxybis(benzenesulfonyl-hydrazide) (OBSH) foaming agent, and
wherein the one or more surfactants includes a silicone-based
surfactant.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This patent application is a divisional application of
pending U.S. patent application Ser. No. 14/989,446 (docket no.
ROC920150242US1), filed Jan. 6, 2016, entitled "EPOXY-BASED RESIN
SYSTEM COMPOSITION CONTAINING A LATENT FUNCTIONALITY FOR POLYMER
ADHESION IMPROVEMENT TO PREVENT SULFUR RELATED CORROSION", which is
hereby incorporated herein by reference in its entirety.
BACKGROUND
[0002] The present invention relates in general to the field of
corrosion protection. More particularly, the present invention
relates to employing an epoxy-based resin system composition
containing a latent functionality for polymer adhesion improvement
in anti-sulfur resistors (ASRs) to prevent corrosion caused by
environmental sulfur components.
SUMMARY
[0003] In accordance with some embodiments of the present
invention, an epoxy-based resin system composition includes a
latent functionality for polymer adhesion improvement. The
composition may, for example, be used to produce an overcoat layer
and/or a protection layer in an anti-sulfur resistor (ASR) for
protecting a metal surface from sulfur related corrosion. In some
embodiments, the composition includes one or more epoxy-based
resins, one or more hardeners and, optionally, one or more blowing
agents and/or one or more filler materials. An epoxide
functionality of at least one of the one or more epoxy-based resins
and a reactive functionality of at least one of the one or more
hardeners react with each other at a first temperature. The latent
functionality, which does not react at the first temperature, is
contained in at least one of the one or more epoxy-based resins,
the one or more hardeners and the one or more filler materials and
reacts in response to another stimulus (e.g., UV light in
conjunction with a UV initiator, such as an onium salt, and/or a
second temperature greater than the first temperature) to enhance
chemical bonding. Optionally, voids created via etching and/or the
one or more blowing agents may be used to enhance mechanical
bonding, alone, or in combination with the one or more filler
materials exposed in the voids.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0004] Embodiments of the present invention will hereinafter be
described in conjunction with the appended drawings, where like
designations denote like elements.
[0005] FIG. 1 is an exploded view of an anti-sulfur resistor (ASR)
that utilizes an epoxy-based resin system composition containing a
latent functionality for polymer adhesion improvement to better
protect metal conductors from corrosion, in accordance with some
embodiments of the present invention.
[0006] FIG. 2 is a sectional view of the anti-sulfur resistor (ASR)
shown in FIG. 1, but which is shown mounted on a printed circuit
board.
[0007] FIG. 3 is a top view of a resistor network array depicting a
plurality of anti-sulfur resistors (ASRs) shown in FIGS. 1 and
2.
[0008] FIG. 4 is a reaction scheme illustrating a method of surface
modifying a silica fiber or a silica particle to contain a latent
functionality (e.g., a secondary amine) for polymer adhesion
improvement, in accordance with some embodiments of the present
invention.
[0009] FIG. 5 is a sectional view of a portion of a cured overcoat
and/or protection layer having a void created via etching or a
blowing agent and in which a surface modified silica fiber is
exposed for polymer adhesion improvement, in accordance with some
embodiments of the present invention.
[0010] FIG. 6 is a flow chart diagram of a method of producing an
anti-sulfur resistor (ASR) that utilizes an epoxy-based resin
system composition containing a latent functionality for polymer
adhesion improvement to better protect metal conductors, in
accordance with some embodiments of the present invention.
DETAILED DESCRIPTION
[0011] The electronics industry designs and tests hardware to be
able to withstand typical indoor environments. Hardware failures
can occur, however, in geographies with harsher indoor environments
than the design set point. This has resulted in electronic
component failure due to corrosion of metallurgy via a corrosive
gas environment. Attempts to mitigate these electronic component
failures have focused on the use of commercially available
conformal coatings. These conformal coatings fall into several
generic classes: silicones, epoxies, acrylates, and other organic
materials. However, accelerated aging testing has revealed that
silicones may actually exacerbate the problem and that corrosion is
merely retarded by the other classes of conformal coatings. The
porous structure of silicone conformal coatings allows the
contaminants to penetrate such coatings. Furthermore, studies have
revealed sulfur components (e.g., elemental sulfur, H.sub.2S, and
sulfur oxides) in the gaseous environment as the major culprit. Of
the sulfur components, elemental sulfur appears to be the most
aggressive. In the case of silicone conformal coatings, research
has found that such coatings are extremely permeable to the sulfur
molecule in the atmosphere and other reduced sulfur species,
leading to sulfidation of silver and copper components mounted on
printed circuit boards.
[0012] Corrosion caused by sulfur components in the air is
especially severe when one or more of the metal conductors that
electrically connect an electronic component is/are a
silver-containing metal. For example, each of the gate resistors of
a resistor network array typically utilizes a silver layer at each
of the gate resistor's terminations. Gate resistors are also
referred to as "chip resistors" or "silver chip resistors".
Typically, gate resistors are coated with a glass overcoat for
corrosion protection. Also for corrosion protection, it is known to
encapsulate gate resistors in a resistor network array by applying
a coating of a conventional room temperature-vulcanizable (RTV)
silicone rubber composition over the entire printed circuit board
on which the resistor network array is mounted. However, the glass
overcoat and conventional RTV silicone rubber compositions fail to
prevent or retard sulfur components in the air from reaching the
silver layer in gate resistors. Hence, any sulfur components in the
air will react with the silver layer in the gate resistor to form
silver sulfide. This silver sulfide formation (often referred to as
silver sulfide "whiskers") produces an electrical open at one or
more of the terminations of the gate resistor and, thereby, failure
of the gate resistor.
[0013] The use of silver as an electrical conductor for
electrically connecting electronic components is increasing because
silver has the highest electrical conductivity of all metals, even
higher than copper. In addition, the concentration of sulfur
components in the air is unfortunately increasing as well. Hence,
the problem of corrosion caused by sulfur components in the air is
expected to grow with the increased use of silver as an electrical
conductor for electrically connecting electronic components and the
increased concentration of sulfur components in the air.
[0014] Having found that silicone conformal coatings are
problematic to the protection of silver-containing resistors due to
the susceptibility of such resistors to being attacked by
sulfur-bearing gases, a switch to anti-sulfur resistors (ASRs) is
underway. These ASRs contain a protection layer that blocks the
exposure of the silver within the resistor from contact with indoor
air environments. This protection layer, which is typically an
epoxy material, is applied atop a silver termination layer. In
conventional ASRs, the protection layer is commonly an epoxy
material that does not bond well with the epoxy overcoat layer or
the platings that are applied on top of the protection layer.
Consequently, the protection layer along with Ni/Sn termination
layers (which are among the platings applied on top of the
protection layer) can peel off the underlying silver termination
layer, thus exposing the underlying silver termination layer to the
indoor air environment that may contain the corrosive sulfur gases.
The underlying silver termination layer is also referred to as the
"upper termination". The upper termination is electrically
connected to a side termination. Both the upper termination and the
side termination include layer that are made from silver (Ag) or a
Ag compound. Hence, a concern is that the upper termination and/or
the side termination could be exposed to the corrosive environment,
which possibly could lead to a cut/open.
[0015] In accordance with some embodiments of the present
invention, an improved polymeric material is incorporated into the
processing of the ASR that will prevent the Ni/Sn layers of the
side termination and the protection layer from peeling off during
use in harsh environments. By fixing this adhesion problem, the ASR
will be more robust and will not be susceptible to corrosion of the
underlying silver termination layer. In accordance with some
embodiments of the present invention, an epoxy-based resin system
composition containing a latent functionality for polymer adhesion
improvement is used to make an enhanced protection layer and/or
overcoat layer that prevents the peeling off of the layers (i.e.,
the protection layer along with the Ni/Sn layers of the side
termination) and, consequently, prevents the underlying silver
termination layer from being attacked by corrosive sulfur-bearing
gases.
[0016] In accordance with some embodiments of the present
invention, an epoxy-based resin system composition includes a
latent functionality for polymer adhesion improvement. The
composition may, for example, be used to produce an overcoat layer
and/or a protection layer in an ASR for protecting a metal surface
from sulfur related corrosion. In some embodiments, the composition
includes one or more epoxy-based resins, one or more hardeners and,
optionally, one or more blowing agents and/or one or more filler
materials. An epoxide functionality of at least one of the one or
more epoxy-based resins and a reactive functionality of at least
one of the one or more hardeners react with each other at a first
temperature. The latent functionality, which does not react at the
first temperature, is contained in at least one of the one or more
epoxy-based resins, the one or more hardeners and the one or more
filler materials and reacts in response to another stimulus (e.g.,
UV light in conjunction with a UV initiator, such as an onium salt,
and/or a second temperature greater than the first temperature) to
enhance chemical bonding. Optionally, voids created via etching
and/or the one or more blowing agents may be used to enhance
mechanical bonding, alone, or in combination with the one or more
filler materials exposed in the voids.
[0017] Epoxy-based resins, which are also referred to herein as
epoxy resins, are reactive monomers, prepolymers or polymers that
contain one or more (typically, two or more) epoxide groups. The
epoxide group is also referred to as a glycidyl or oxirane group.
Epoxy resins may be reacted (i.e., cross-linked) with a wide
variety of co-reactants including, but not limited to, amines,
acids, anhydrides, phenols, alcohols and thiols. Such co-reactants
are often referred to as hardeners or curing agents. Typically, the
cross-linking reaction between epoxy resins and the co-reactants is
referred to as curing.
[0018] Suitable epoxy-based resins include, but are not limited to,
bisphenol A epoxy resins, bisphenol F epoxy resins, novolac epoxy
resins, aliphatic epoxy resins, cycloaliphatic epoxy resins,
glycidylamine epoxy resins, polyglycol di-epoxide liquid resins,
phenyl glycidyl ether, epoxy resin blends (e.g., blends of one or
more cycloaliphatic epoxy resins and one or more non-cycloaliphatic
epoxy resin blends), and the like.
[0019] Bisphenol A epoxy resins, which are typically produced from
the reaction of bisphenol A (BPA) and epichlorohydrin, are
commercially available. Bisphenyl A diglycidyl ether (BADGE), which
is the simplest bisphenol A epoxy resin, is formed from reacting
one mole of BPA and two moles of epichlorohydrin. Suitable
bisphenol A epoxy resins include, but are not limited to,
BADGE.
[0020] Bisphenol F epoxy resins, which are typically produced from
the reaction of bisphenol F (BPF) and epichlorohydrin, are
commercially available. Bisphenyl F diglycidyl ether (BFDGE), which
is the simplest bisphenol F epoxy resin, is formed from reacting
one mole of BPF and two moles of epichlorohydrin. Suitable
bisphenol F epoxy resins include, but are not limited to,
BFDGE.
[0021] Novolac epoxy resins, which are typically produced from the
reaction of phenols with formaldehyde and subsequent glycidylation
with epichlorohydrin, are commercially available. Suitable novolac
epoxy resins include, but are not limited to, epoxy phenol novolacs
(EPNs) and epoxy cresol novolacs (ECNs).
[0022] Aliphatic epoxy resins, which are typically produced by
glycidylation of aliphatic alcohols or polyols, are commercially
available. Suitable aliphatic epoxy resins include, but are not
limited to, monofunctional aliphatic epoxy resins such as dodecyl
and tetradecyl glycidyl ethers (CAS Number 68609-97-2),
difunctional aliphatic epoxy resins such as butanediol diglycidyl
ether (CAS Number 2425-79-8), and higher functional aliphatic epoxy
resins such as trimethylolpropane triglycidyl ether (CAS Number
3454-29-3).
[0023] Cycloaliphatic epoxy resins, which are related to aliphatic
epoxy resins but contain one or more cycloaliphatic rings in the
molecule, are commercially available. The reactivity of
cycloaliphatic epoxy resins is rather low compared to other classes
of epoxy resin. Hence, one or more cycloaliphatic epoxy resins may
serve as the latent functionality in accordance with some
embodiments of the present invention. That is, the latent
functionality may be contained in at least one of the one or more
epoxy-based resins (i.e., also referred to herein as a "latent
epoxy") of the epoxy-resin based system composition. An
illustrative example of a suitable cycloaliphatic epoxy resin is
diglycidyl 1,2-cyclohexanedicarboxylate (CAS Number 5493-45-8),
which is a diglycidyl ester of hexahydrophthalic acid. Another
illustrative example of a suitable cycloaliphatic epoxy resin is
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (CAS
Number 2386-87-0).
[0024] Of the two exemplary cycloaliphatic epoxy resins referred to
above, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate is
significantly more reactive than diglycidyl
1,2-cyclohexanedicarboxylate because the ring strain in the former
that is absent from the latter. Accordingly, diglycidyl
1,2-cyclohexanedicarboxylate is referred to herein as a "latent
epoxy" relative to
3,4-epoxycyclohexylmethyl-3,4-epoxycyclo-hexanecarboxylate.
[0025] Either or both of these two exemplary cycloaliphatic epoxy
resins may be utilized along with one or more suitable anhydride
hardeners, for example, to provide a cycloaliphatic epoxy
resin/anhydride system. Suitable anhydride hardeners include, but
are not limited to, hexahydrophthalic anhydride (HHPA) (CAS Number
85-42-7) and N,N-dimethylbenzylamine (BMDA) (CAS Number
103-83-3).
[0026] Glycidylamine epoxy resins, which are typically produced
from the reaction of aromatic amines and epichlorohydrin, are
commercially available. Typically, glycidylamine epoxy resins are
highly reactive. Suitable glycidylamine epoxy resins include, but
are not limited to, N,N-diglycidyl-4-glycidyloxyaniline (CAS Number
5026-74-4) and 4,4'-methylenebis-(N,N-diglycidylaniline) (CAS
Number 28768-32-3).
[0027] Depending on the application, flexible resins such as
polyglycol di-epoxide liquid resins may be preferred to impart
flexibility. Polyglycol di-epoxide liquid resins, which are
produced from the reaction of polypropylene glycol and
epichlorohydrin, are commercially available.
[0028] Phenyl glycidyl ether (CAS Number 122-60-1) is another
suitable commercially available epoxy-based resin.
[0029] As mentioned above, epoxy resin blends of one or more
cycloaliphatic epoxy resins and one or more non-cycloaliphatic
epoxy resins may be utilized in accordance with some embodiments of
the present invention. In an illustrative example, of suitable
epoxy resin blends may be provided by utilizing a blend of
diglycidyl 1,2-cyclohexanedicarboxylate (CAS Number 5493-45-8)
[i.e., one of the two exemplary cycloaliphatic epoxy resins] and
N,N-diglycidyl-4-glycidyloxyaniline (CAS Number 5026-74-4) [a
glycidylamine epoxy resin] (along with one or more suitable curing
agents, for example, to provide a cycloaliphatic epoxy
resin/non-cycloaliphatic epoxy resin/anhydride system). Of these
two epoxy-based resins, N,N-diglycidyl-4-glycidyloxyaniline is
significantly more reactive than diglycidyl
1,2-cyclohexanedicarboxylate because the former is a highly
reactive glycidylamine epoxy resin while the latter is a
cycloaliphatic epoxy resin. Accordingly, diglycidyl
1,2-cyclohexanedicarboxylate is referred to herein as a "latent
epoxy" relative to N,N-diglycidyl-4-glycidyloxyaniline. In such a
cycloaliphatic epoxy resin/non-cycloaliphatic epoxy resin/anhydride
system, suitable curing agents include, but are not limited to,
methyltetrahydrophthalic anhydride (MTHPA) (CAS Number 11070-44-3
or 26590-20-5) and methyl-5-norbornene-2,3-dicarboxylic anhydride
(CAS Number 25134-21-8) (also referred to as Nadic.RTM. Methyl
Anhydride (NMA)).
[0030] The addition of a hardening agent to the epoxy-based resin
causes the liquid resin to cure or harden to a rigid (typically)
cross-linked polymer. When the epoxy-based resin is intimately
mixed with a stoichiometric amount of a hardening agent containing
labile hydrogen atoms, the epoxy ring opens and reacts with the
hardening agent. Common classes of hardeners for epoxy-based resins
include amines, acids, acid anhydrides, phenols, alcohols and
thiols. Relative reactivity (lowest to the highest) is typically in
the order: phenols<anhydrides<aromatic
amines<cycloaliphatic amines<aliphatic amines<thiols.
Hence, one or more classes of hardeners may serve as the latent
functionality in accordance with some embodiments of the present
invention. That is, the latent functionality may be contained in at
least one of the one or more hardeners (i.e., also referred to
herein as a "latent hardener") of the epoxy-resin based system
composition. Accordingly, an aromatic amine may be referred to as a
"latent amine" relative to a cycloaliphatic amine or an aliphatic
amine. Moreover, hardeners with only secondary amines are generally
relatively less reactive than hardeners with primary amines. In
fact, the reactivity of the primary amine is approximately double
that of the secondary amine.
[0031] The relative rate of reaction "k.sub.rel" of each of various
amines with phenyl glycidyl ether at 50.degree. C., as disclosed in
Table 10.1 of Thomas et al., "Micro- and Nanostructured
Epoxy/Rubber Blends," Wiley-VCH Verlag GmbH & Co., Weinheim,
Germany, 2014, pp. 197, is illustrative. For example, the rates of
reaction of exemplary amines with phenyl glycidyl ether (an
exemplary epoxy-based resin) at 50.degree. C. are as follows:
[0032] Amino-ethylpiperazine (k.sub.rel=65.3)
[0033] N-Methylcyclohexylamine (k.sub.rel=14.9)
[0034] Aniline (k.sub.rel=1.0)
[0035] N-Ethylpiperazine (k.sub.rel=42.0)
[0036] Benzylamine (k.sub.rel=11.3)
[0037] N,N,N'-Trimethylethylene-diamine (k.sub.rel=29.7)
[0038] Neopenylamine (k.sub.rel=13.6)
[0039] N,N'-Dimethylethylenediamine (k.sub.rel=47.3)
[0040] Amino-ethylpiperidine (k.sub.rel=15.4)
[0041] Cyclohexylamine (k.sub.rel=10.9)
[0042] N-Methylaniline (k.sub.rel=0.45)
[0043] Morpholine (k.sub.rel=18.5)
[0044] N,N'-Diethyl-1,2-ethanediamine (k.sub.rel=20.3)
[0045] N,N,N,N'-Tetramethyl-diethylenetriamine (k.sub.rel=11.7)
[0046] Methoxy-ethylamine (k.sub.rel=11.0)
[0047] Most cured epoxy foams (also referred to herein as "blown
epoxy") are produced using one of three types of hardening agents,
which are amines, polyphenols, and anhydrides. Aside from one or
more epoxy-based resins and one or more hardeners, other
constituents used to make epoxy foams typically include a blowing
agent, a surfactant, and one or more filler materials or nucleating
agents (hereinafter referred to as one or more "filler materials").
Epoxy foams comprising a plurality of resins, a plurality of curing
agents, at least one blowing agent, at least one surfactant and
optionally at least one filler, as well as processes for making the
same, are disclosed in U.S. Pat. No. 6,110,982, which is hereby
incorporated herein by reference in its entirety.
[0048] Blowing agents, which are also referred to as "foaming
agents", typically are chemical blowing agents that release either
nitrogen gas or carbon dioxide gas through decomposition when
heated. Suitable chemical blowing agents include, but are not
limited to, ammonium carbonate, sodium bicarbonate, and sulfonyl
hydrazide. Other suitable chemical blowing agents include, but are
not limited to, azodicarbonamide (ADC) foaming agents and
p-p'-oxybis(benzenesulfonyl-hydrazide) (OBSH) foaming agents.
Suitable ADC foaming agents include, but are not limited to,
CELOGEN AZ-120 (average particle diameter 3-5.5 .mu.m), CELOGEN
AZ-130 (average particle diameter 5-6 .mu.m), CELOGEN AZ-150
(average particle diameter 8-10 .mu.m), and CELOGEN AZ-1901
(average particle diameter 14.1-16 .mu.m) available from CelChem
LLC, Baton Rouge, La. Suitable OBSH foaming agents include, but are
not limited to, CELOGEN OT (Oil Treated) (average particle diameter
5-15 .mu.m) available from CelChem LLC, Baton Rouge, La. A chemical
blowing agent may be selected based on, at least in part, its
decomposition temperature (i.e., the temperature at which the
blowing agent releases gas). For example, CELOGEN OT, which has a
decomposition temperature of approximately 153-167.degree. C., is a
relatively low temperature blowing agent as compared to the CELOGEN
AZ products, which have a decomposition temperature of
approximately 190-220.degree. C. The blowing agent may be mixed
into the epoxy-based resin using a Banbury mixer.
[0049] Alternatively, the blowing agent may be a physical blowing
agent. Suitable physical blowing agents include, but are not
limited to, liquid solvents such as pentane, toluene, fluorocarbons
(FCs), chlorofluorocarbons (CFCs), and hydrochlorofluorocarbons
(HCFCs).
[0050] Surfactants are used in epoxy-based resin system
compositions to promote foaming and stabilization of the subsequent
void structure. A surfactant generally serves to decrease the
surface tension of the pre-cure composition and thereby promote
increased expansion, smaller voids, and more uniform void size and
texture of the resultant blown epoxy. The surfactants used in
polyurethane foam systems, such as silicone-based surfactants, may
generally be used in epoxy-based resin system compositions. The
void structure can be greatly affected by the surfactant, which in
turn influences the properties of the resultant blown epoxy.
[0051] Filler materials may be added to the epoxy-based resin
system composition for reasons including improving mechanical
bonding, as well as lowering cost, adding color, reducing
exotherms, and controlling shrinkage rates. Suitable filler
materials include, but are not limited to, silica fibers, silica
particles, carbon black, TiO.sub.2, ZnO, and combinations thereof.
These filler materials may be neat or surface modified to contain
the latent functionality. For example, modified silica fibers may
be either pre-blend modified (i.e., silica fibers are surface
modified to contain the latent functionality before the silica
fibers are blended into the epoxy-based resin system composition)
or post-exposure modified (i.e., silica fibers are surface modified
to contain the latent functionality after being exposed in the
voids on the surface of the etched/blown epoxy).
[0052] Fillers in the form of fine particles (e.g., carbon black
and fumed silica) may also serve as nucleating agents. Small
particles provide sites for heterogeneous nucleation which allows
for initiation and subsequent growth of foam voids. In
heterogeneous nucleation, gas molecules driven by supersaturation
preferentially form nucleation sites on the solid/fluid interfaces
of the nucleation agent. The ultimate void size is determined by
other factors including the exotherm, the rate of cure, the amount
of blowing agent, and interactions between the epoxy-based resin
and the surfactant.
[0053] While embodiments of the present invention are described
herein in the context of an epoxy-based resin system composition
containing a latent functionality for polymer adhesion improvement,
the present invention is not so limited. Other polymeric materials
containing a latent functionality for polymer adhesion improvement
may be used in lieu of, or in addition to, an epoxy-based resin
system composition. For example, silicones, acrylates, and other
organic materials containing a latent functionality for polymer
adhesion improvement may be used in lieu of, or in addition to, an
epoxy-based resin system composition.
[0054] In accordance with some embodiments of the present
invention, an improved polymeric material is used to produce an
overcoat layer and/or a protection layer in an anti-sulfur resistor
(ASR). This results in an enhanced ASR that is peel-resistant. In
general, standard processes used to create conventional ASRs may be
used to form the peel-resistant ASR.
[0055] One skilled in the art will appreciate, however, that
applications for the improved polymeric material are not limited to
the production of the overcoat layer and/or the protection layer in
ASRs. The improved polymeric material may be used to produce other
polymeric layers associated with ASRs (e.g., a polymer conformal
coating that overlies a network resistor array), as well as other
electronic components that have metal conductors that are
susceptible to being attacked by corrosive sulfur-bearing
gases.
[0056] In conventional ASRs, as noted above, the protection layer
is commonly an epoxy material that does not bond well with the
epoxy overcoat layer or the platings (i.e., the Ag plating layer of
the side termination and the Ni/Sn plating layers of the side
termination) that are applied on top of the protection layer. This
situation is corrected, in accordance with some of the embodiments
of the present invention, through the use of a resin-based epoxy
system composition that includes a latent functionality for polymer
adhesion improvement and through the use of strategies such as
etching for mechanical bonding improvement.
[0057] In accordance with some embodiments of the present
invention, an overcoat layer is applied to at least a portion of
the resistor element and a first portion of the Ag layer of the
upper termination. After the overcoat layer is applied and cured,
at least a portion of the cured overcoat layer may be modified via
an etching process. The cured overcoat layer may be etched in its
entirety or locally in one or more critical areas (e.g., regions
where the protection layer will be subsequently applied). The
etching process may be mechanical and/or chemical. For example, the
cured overcoat layer may be etched using a mechanical etching
process such as bead blasting or polishing. Alternatively, the
cured overcoat layer may be etched using a chemical etching process
such as acid etching, alkaline etching, permanganate etching, or
gas plasma etching. The etching process creates a rough surface
(i.e., voids) on the surface of the cured overcoat layer.
Additionally, in accordance with some embodiments of the present
invention, the overcoat layer is a functionalized epoxy layer that
contains a latent functionality (i.e., latent amine groups and/or
latent epoxy groups). After etching, the epoxy protection layer is
then applied and cured. When the protection layer is applied, it is
able to flow into the voids of the roughened surface of the epoxy
overcoat layer to form a mechanical interlock (i.e., a mechanical
bond between the protection layer and the overcoat layer). In
addition, because the overcoat layer has functional groups (i.e.,
the latent functionality), chemical bonding between protection
layer and the latent amine groups and/or the latent epoxy groups of
the overcoat layer will occur. This chemical and mechanical bond
ensures that the protection layer will not be able to peel.
[0058] Further, after the protection layer is applied and cured,
the protection layer can then be etched to allow mechanical
interlocks to be formed when the Ag or Ag compound layer, the Ni or
Ni compound layer, and the Sn or Sn compound layer of the side
termination are applied to the protection layer. That is,
mechanical interlocks may be formed between the protection layer
and the Ag layer of the side termination, between protection layer
and the Ni layer of the side termination, and between the
protection layer and the Sn layer of the side termination.
[0059] In accordance with some embodiments, the overcoat layer
contains a blowing agent that allows the overcoat layer to form
voids (similar to the pores in foams) which then allows the layers
to form mechanical interlocks when the protection layer and the
platings are applied to the overcoat layer. For example, a
mechanical bond may be formed between the overcoat layer and the
protection layer, between the overcoat layer and the Ni layer of
the side termination, and between the overcoat layer and the Sn
layer of the side termination.
[0060] Further, the overcoat layer and/or the protection layer may
contain one or more modified filler materials (e.g. silica fibers
or silica particles surface modified to contain latent epoxy or
amine functionalities), and when etched or otherwise exposed (e.g.,
via a blowing agent), the modified filler materials will allow for
chemical bonding between the two epoxy layers (i.e., between the
overcoat layer and the protection layer). The modified filler
material when exposed additionally can act as a "hook" type
structure that will allow the protection layer to have better
mechanical bonding to the overcoat layer. The modified filler
material may be pre-blend modified (i.e., the filler material is
surface modified to contain the latent functionality before the
filler material is blended into the epoxy-based resin system
composition) or post-exposure modified (i.e., the filler material
is surface modified to contain the latent functionality after being
exposed in the void on the surface of the cured overcoat layer
and/or protection layer).
[0061] Alternatively, the overcoat layer and the protection layer
could be filler-free and only have the latent functionality for
chemical bonding integrated into the epoxy networks of the overcoat
layer and the protection layer. Additionally, as described above,
mechanical bonding between such filler-free overcoat and protection
layers may be enhanced via etching or through the use of a blowing
agent.
[0062] The latent functionality can be reacted either by heat or UV
curing methods that are not used to initially cure the epoxy resin.
For example, the epoxy resin (e.g., phenyl glycidyl ether) used to
produce the overcoat layer may be blended with a hardener
containing a relatively more reactive amine such as
amino-ethylpiperazine (k.sub.rel=65.3) that requires 50.degree. C.
curing temperatures (i.e., the hardener and the epoxy resin react
with each other in the initial cure at 50.degree. C.) and another
hardener (and/or one or more modified filler materials) containing
a latent amine functionality that is relatively less reactive
(e.g., a secondary amine) such as N,N'-diethyl-1,2-ethanediamine
(k.sub.rel=20.3) and requires higher heat (or UV light in
conjunction with a UV initiator, such as an onium salt) to cure. In
this example, k.sub.rel is the relative rate of reaction
"k.sub.rel" of a given amine with phenyl glycidyl ether at
50.degree. C. Similarly, the epoxy resin used to produce the
protection layer may also be blended with a hardener containing the
latent amine functionality. This ensures that the functionalities
that have been added respond only when desired (e.g., when the
protection layer is cured). Unless there is a UV initiator, UV
light will not initiate curing of the latent hardener. Onium salt
is the most common UV initiator. In this example, the formulation
used to produce the overcoat layer and/or protection layer would
need to contain a thermally stable onium salt or other UV
initiator. Fortunately, the most common onium salts are very
thermally stable. For example, one or more of the hardeners may be
a UV initiator, such as an onium salt.
[0063] Alternatively, the same hardener may contain both the
relatively more reactive amine and the relatively less reactive
amine (i.e., the latent amine functionality). For example, such a
hardener may contain both a primary amine (which is a relatively
more reactive amine) and a secondary amine (which is a relatively
less reactive amine).
[0064] Also, as mentioned above, in some embodiments of the present
invention, one or more modified filler materials may contain the
latent amine functionality. For example, the epoxy resin (e.g.,
phenyl glycidyl ether) used to produce the overcoat layer may be
blended with a hardener containing a relatively more reactive amine
such as amino-ethylpiperazine (k.sub.rel=65.3) that requires
50.degree. C. curing temperatures (i.e., the hardener and the epoxy
resin react with each other in the initial cure at 50.degree. C.)
and one or more modified filler materials containing a latent amine
functionality that is relatively less reactive (e.g., a secondary
amine) and requires higher heat (or UV light in conjunction with a
UV initiator) to cure. Silica fibers or particles may be modified
via silane surface modification using Dow Corning.RTM. Z-6032
Silane, for example, which contains secondary amines as the latent
functionality. Alternatively, as mentioned above, the latent
functionality could be added in a subsequent step to the surface of
the etched/blown epoxy surface. For example, silica fibers or
particles exposed on the etched/blown epoxy surface may be modified
after they are exposed on the etched/blown epoxy surface. Here too,
the silica fibers or particles may be modified via silane surface
modification using Dow Corning.RTM. Z-6032 Silane, for example,
which contains a secondary amine as the latent functionality.
[0065] Some embodiments of the present invention are described
herein in the context of protecting metal conductors of an
exemplary anti-sulfur resistor (ASR) in a resistor network array
from corrosion caused by sulfur components in the air. An exemplary
ASR and resistor network array are depicted in FIGS. 1-3. One
skilled in the art will appreciate, however, that the present
invention can also apply to protecting metal conductors of ASRs and
resistor network arrays having configurations differing from the
ASR and resistor network array shown in FIGS. 1-3 and to protecting
metal conductors of gate resistors and other electronic components,
and, more generally, to protecting a metal surface of any
product.
[0066] Referring now to FIG. 1, there is depicted, in an exploded
view, an anti-sulfur (ASR) 100 of a resistor network array 300
(shown in FIG. 3) that utilizes an epoxy-based resin system
composition containing a latent functionality for polymer adhesion
improvement to protect metal conductors from corrosion, in
accordance with some embodiments of the present invention. FIG. 2
is a sectional view of the anti-sulfur resistor (ASR) 100 shown in
FIG. 1, but which is shown mounted on a printed circuit board 210.
FIG. 3 is a top view of a resistor network array 300 that includes
a plurality of the anti-sulfur resistors (ASRs) shown in FIGS. 1
and 2.
[0067] As shown in FIGS. 1 and 2, a resistor element 102 is mounted
to a substrate 104, such as a ceramic substrate. The anti-sulfur
resistor 100 includes two termination structures 110, each
typically comprising a Ag (silver) (or Ag compound) layer 111 of an
upper termination, a Ag (silver) (or Ag compound) layer 112 of a
side termination, a Ni (nickel) (or Ni compound) layer 114 of the
side termination, and a Sn (tin) (or Sn compound) layer 116 of the
side termination. Each of the termination structures 110 of the
anti-sulfur resistor 100 is also referred to herein as a "metal
conductor".
[0068] For corrosion protection, in accordance with some
embodiments of the present invention, each ASR 110 in a resistor
network array is coated with a polymer overcoat layer 120 and a
polymer protection layer 121. The overcoat layer 120 and/or the
protection layer 121, in accordance with some embodiments of the
present invention, is/are produced using an epoxy-based resin
system composition includes a latent functionality for polymer
adhesion improvement to protect the silver components in the
termination structure 110 from sulfur related corrosion. In some
embodiments, the epoxy-based resin system composition includes one
or more epoxy-based resins, one or more hardeners and, optionally,
one or more blowing agents and/or one or more filler materials. An
epoxide functionality of at least one of the one or more
epoxy-based resins and a reactive functionality of at least one of
the one or more hardeners react with each other at a first
temperature. The latent functionality, which does not react at the
first temperature, is contained in at least one of the one or more
epoxy-based resins, the one or more hardeners and the one or more
filler materials and reacts in response to another stimulus (e.g.,
UV light in conjunction with a UV initiator and/or a second
temperature greater than the first temperature) to enhance chemical
bonding. Optionally, voids created via etching and/or the one or
more blowing agents may be used to enhance mechanical bonding,
alone, or in combination with the one or more filler materials
exposed in the voids.
[0069] The ASRs in a resistor network array are typically soldered
to a printed circuit board by SMT (surface mounting technology)
processes. As best seen in FIG. 2, the termination structures 110
of each ASR 100 in the resistor network array 300 (shown in FIG. 3)
are soldered to corresponding terminals or pads 212 on the printed
circuit board 210. For example, the Sn layer 116 (solder) of the
termination structures 110 of each ASR 100 may be reflowed to join
(i.e., electrically and mechanically) the termination structures
110 on the base of the ASR 100 with the corresponding terminals or
pads 212 on the printed circuit board 210.
[0070] Optionally, as shown in FIG. 2, after each ASR 100 is
mounted on the printed circuit board 210, a conformal coating 130
may be applied. The conformal coating 130 may be produced using a
conventional composition (e.g., a conventional RTV silicone rubber
composition) or, alternatively, an epoxy-based resin system
composition that includes a latent functionality for polymer
adhesion improvement in accordance with some embodiments of the
present invention.
[0071] Conformal coatings typically fall into several generic
classes: silicones, epoxies, acrylates, and other organic
materials. For example, the conformal coating 130, if present, may
be produced using a conventional RTV silicone rubber composition,
such as Dow Corning.RTM. 1-2620 RTV Coating or Dow Corning.RTM.
1-2620 Low VOC RTV Coating. Typically, it is desirable for the
conformal coating 130 to be non-water absorbing to avoid shorting
from occurring through pathways created by water. It may also be
desirable for the conformal coating 130 to be halogen-free (i.e.,
RoHS compliant).
[0072] As best seen in FIG. 3, in accordance with some embodiments
of the present invention, the conformal coating 130 covers
essentially the entire printed circuit board 210, encapsulating
each of the ASRs 100 of the resistor network array 300 (as well as
any other discrete electronic component(s) mounted on the board
210). Alternatively, the conformal coating 130 may cover only one
or more specific areas of the printed circuit board 210.
[0073] Advantageously, existing deposition processes may be used
for applying the overcoat layer 120 and/or protection layer 121. In
general, standard processes used to create conventional ASRs may be
used to form a peel-resistant ASR in accordance with some
embodiments of the present invention.
[0074] FIG. 4 is a reaction scheme illustrating a method of surface
modifying a silica fiber or a silica particle to contain a latent
functionality (e.g., a secondary amine) for polymer adhesion
improvement, in accordance with some embodiments of the present
invention. In the reaction scheme shown in FIG. 4, silica fibers or
particles are surface modified via silane surface modification
using a silane coupling agent having two secondary amine groups,
e.g., vinylbenzylethylenediaminepropyltrimethoxysilane
hydrochloride (CAS Number 171869-89-9). The resulting modified
silica fibers or particles contain secondary amines as the latent
functionality.
[0075] The particular silane reactant (i.e.,
vinylbenzylethylenediaminepropyltri-methoxysilane hydrochloride)
shown in FIG. 4 is set forth for the purpose of illustration, not
limitation. Those skilled in the art will appreciate that other
silane coupling agents having one or more secondary amine groups
may be utilized in lieu of, or in addition to,
vinylbenzylethylenediaminepropyltrimethoxysilane hydrochloride. For
example, trimethoxy[3-(methyl-amino)propyl]-silane (CAS Number
3069-25-8) or N-[3-(trimethoxysilyl)propyl]ethylene-diamine (CAS
Number 1760-24-3) may be used in lieu of, or in addition to,
vinylbenzylethylenediaminepropyltrimethoxysilane hydrochloride.
Note N-[3-(trimethoxysilyl)-propyl]ethylenediamine is a silane
coupling agent that has a primary amine, as well as a secondary
amine.
[0076] Only one silane coupling agent reaction site is illustrated
in FIG. 4 for the sake of clarity. Each silane coupling agent
reaction site includes a silicon atom that attaches onto the silica
fiber or particle surface, via one, two or three bonds (only one
bond is shown, but three bonds are typical) each formed at an
available hydroxyl group on the surface of the silica fiber or
particle. While only one silane coupling agent reaction site is
illustrated in FIG. 4, it is typically desirable to react a
quantity of the silane sufficient to react with all of the
available hydroxyl groups on the surface of the silica fiber or
particle. Hence, it is typically desirable to determine the number
of available hydroxyl groups on the surface of the silica fiber or
particle and then, in turn, determine a quantity of silane coupling
agent sufficient to react with all of those available hydroxyl
groups. Generally, stoichiometric quantities of the reactants may
be used in the reaction scheme shown in FIG. 4 (i.e., one silicon
atom/three available hydroxyl groups). However, the relative
quantity of the reactants may be adjusted in the reaction scheme
shown in FIG. 4 to achieve a desired level of functionalization
(e.g., 5-10 wt %).
[0077] The silica fibers or particles may be reacted with Dow
Corning.RTM. Z-6032 Silane, for example, using conventional silane
surface modification techniques well known to those skilled in the
art. Dow Corning.RTM. Z-6032 Silane contains 1,2-ethanediamine,
N-[3-(trimethoxysilyl)propyl]-, N'-[(ethylphenyl)methyl]
derivatives, hydrochlorides (CAS Number 171869-89-9) (30-50%),
along with methanol (50-70%) and
N-[3-(trimethoxysilyl)propyl]-ethylenediamine (CAS Number
1760-24-3) (10-20%). This reaction may be performed at room
temperature using conventional procedures well known to those
skilled in the art. The reaction conditions may be either acidic or
basic. For example, the reaction may be performed in an acid bath
having a pH of approximately 4.5. Either HCl or acetic acid, for
example, may be used to drop the pH to 4.5 or lower. Alternatively,
the reaction may be performed in a bath having a basic pH. In this
case, a pH of 7-12 is preferred, most preferred is pH=10. Either
ammonium or sodium hydroxide, for example, may be used to raise the
pH to 7 or higher. In either case, the reaction is typically
performed in the presence of ethanol (or methanol) and water.
Typically, methanol is preferred for trimethoxysilanes, while
ethanol is preferred for triethoxysilanes.
[0078] The silica fiber or particle shown in FIG. 4 is set forth
for the purpose of illustration, not limitation. One skilled in the
art will appreciate that other filler materials may be used in lieu
of, or in addition to, silica fibers or particles. For example,
carbon black, TiO.sub.2, ZnO and myriad other conventional filler
materials may be used in lieu of, or in addition to, silica fibers
or particles. Suitable filler materials contain surface hydroxyl
groups that can condense with the silane (e.g., Dow Corning.RTM.
Z-6032 Silane).
[0079] FIG. 5 is a sectional view of a portion of a cured overcoat
and/or protection layer 505 having a void 510 created via etching
or a blowing agent and in which a surface modified silica fiber 515
is exposed for polymer adhesion improvement, in accordance with
some embodiments of the present invention. The cured layer 505
shown in FIG. 5 may correspond to the overcoat layer 120 and/or the
protection layer 121 shown in FIGS. 1 and 2. As shown in FIG. 5, in
an enlarged view, the modified silica fiber 515 is surface modified
to contain secondary amine groups as the latent functionality. The
modified silica fiber 515 may be either pre-blend modified (i.e., a
silica fiber is surface modified to contain the latent
functionality before the silica fiber is blended into the
epoxy-based resin system composition) or post-exposure modified
(i.e., a silica fiber is surface modified to contain the latent
functionality after being exposed in the void 510 on the surface of
the cured layer 505).
[0080] The modified silica fiber 515 may be provided, for example,
using the reaction scheme shown in FIG. 4. That is, the modified
silica fiber 515 may be provided via silane surface modification
(in either pre-blend modified embodiments or post-exposure modified
embodiments) of silica fibers using
vinylbenzylethylenediaminepropyltrimethoxy-silane hydrochloride
(CAS Number 171869-89-9) as the silane coupling agent.
[0081] Only one silane coupling agent reaction site is illustrated
in FIG. 5 for the sake of clarity. Each silane coupling agent
reaction site includes a silicon atom that attaches onto the
surface of silica fiber 515, via one, two or three bonds (only one
bond is shown, but three bonds are typical) each formed at an
available hydroxyl group on the surface of the silica fiber or
particle. While only one silane coupling agent reaction site is
illustrated in FIG. 5, it is typically desirable to react a
quantity of the silane sufficient to react with all of the
available hydroxyl groups on the surface of the silica fiber 515.
Hence, it is typically desirable to determine the number of
available hydroxyl groups on the surface of the silica fiber 515
and then, in turn, determine a quantity of silane coupling agent
sufficient to react with all of those available hydroxyl groups.
Generally, stoichiometric quantities of the reactants may be used
in the reaction scheme shown in FIG. 4 (i.e., one silicon
atom/three available hydroxyl groups). However, the relative
quantity of the reactants may be adjusted in the reaction scheme
shown in FIG. 4 to achieve a desired level of functionalization
(e.g., 5-10 wt %).
[0082] Hydroxy-functionalities from ring-opening the oxirane on the
epoxy-based resin (e.g. phenyl glycidyl ether) will react with the
amine (i.e., the "latent amine") on the silane attached to the
filler material. This latent functionality does not react at the
first temperature used for the initial curing/cross-linking.
Rather, this reaction will only occur in a final
curing/cross-linking in response to a stimulus not used in the
initial curing/cross-linking. Heat (i.e., a second temperature
greater than the first temperature used for the initial
curing/cross-linking) and/or UV light (i.e., in conjunction with a
UV initiator) could be used for the final curing/cross-linking.
[0083] The surface modified silica fiber 515 shown in FIG. 5 is set
forth for the purpose of illustration, not limitation. One skilled
in the art will appreciate that other filler materials may be used
in lieu of, or in addition to, surface modified silica fibers. For
example, surface modified silica particles may be used in lieu of,
or in addition to, surface modified silica fibers.
[0084] FIG. 6 is a flow chart diagram of a method 600 of producing
an anti-sulfur resistor (ASR) that utilizes an epoxy-based resin
system composition containing a latent functionality for polymer
adhesion improvement to better protect metal conductors, in
accordance with some embodiments of the present invention. Method
600 sets forth the preferred order of steps. It must be understood,
however, that the various steps (i.e., steps 605-645) may occur
simultaneously or at other times relative to one another. For
example, this process may occur before the resistors are mounted to
a substrate. In such an example, the entire ASR may be formed
first, followed by mounting the ASR to the substrate, and then
conformal coating. Optional steps (i.e., steps 620, 625 and 640)
are denoted in boxes with dashed lines.
[0085] Method 600 begins by providing an electronic component
mounted on a substrate and electrically connected by metal
conductors in the form of an upper silver termination layer (step
605). For example, referring temporarily to FIGS. 1 and 2, the
electronic component may correspond to the resistor element 102
mounted on the substrate 104 and electrically connected by metal
conductors in the form of the silver termination layer (upper
termination) 111.
[0086] Method 600 continues by applying an epoxy-based resin system
composition over at least a portion of the electronic component and
a first portion of the metal conductors (step 610). For example,
step 610 may correspond to applying an epoxy-based resin system
composition that includes a latent functionality. The epoxy-based
resin system composition may be applied using conventional
deposition processes well known to those skilled in the art. In
some embodiments, the epoxy-based resin system composition includes
one or more epoxy-based resins, one or more hardeners and,
optionally, one or more blowing agents and/or one or more filler
materials. An epoxide functionality of at least one of the one or
more epoxy-based resins and a reactive functionality of at least
one of the one or more hardeners react with each other at a first
temperature. The latent functionality, which does not react at the
first temperature, is contained in at least one of the one or more
epoxy-based resins, the one or more hardeners and the one or more
filler materials and reacts in response to another stimulus (e.g.,
UV light in conjunction with a UV initiator and/or a second
temperature greater than the first temperature) to enhance chemical
bonding between an overcoat layer (which will be produced from this
epoxy-based resin system composition) and a protection layer (which
will be produced from a subsequently applied (step 630, described
below) epoxy-based resin system formulation).
[0087] Then, the method 600 continues by curing (and, optionally,
blowing), at a first temperature, the epoxy-based resin system
composition to produce an overcoat layer (step 615). For example,
referring temporarily to FIGS. 1 and 2, step 615 may correspond to
curing an epoxy-based resin system composition that includes a
latent functionality for polymer adhesion improvement to produce
the overcoat layer 120. At the first temperature, as noted above,
an epoxide functionality of at least one of the one or more
epoxy-based resins and a reactive functionality of at least one of
the one or more hardeners react with each other. In embodiments
where the epoxy-based resin system composition includes one or more
blowing agents, curing the epoxy-based resin system composition
also blows (foams) the epoxy-based resin system composition
creating voids (e.g., 510 in FIG. 5) on the surface of the overcoat
layer.
[0088] Optionally, the cured overcoat layer may then be etched
(step 620). In this optional step, the cured overcoat layer may be
modified via an etching process in its entirety or locally in one
or more critical areas (e.g., regions where the protection layer
and the various platings of the side termination will be
subsequently applied). The etching process may be mechanical and/or
chemical. For example, the cured overcoat layer may be etched using
a mechanical etching process such as bead blasting or polishing.
Such mechanical etching processes are conventional and well known
to those skilled in the art. Alternatively, the cured overcoat
layer may be etched using a chemical etching process such as acid
etching, alkaline etching, permanganate etching, or gas plasma
etching. Such chemical etching processes are conventional and well
known to those skilled in the art. The etching process creates a
rough surface (e.g., voids 510 in FIG. 5) on the surface of the
cured overcoat layer.
[0089] Optionally, in embodiments where the epoxy-based resin
system composition includes one or more filler materials that are
neat (i.e., not pre-blend modified), the filler material exposed on
the etched/blown epoxy surface of the cured overcoat layer is
silane modified (step 625). In this optional step, the filler
material exposed on the etched/blown epoxy surface of the cured
overcoat layer may be, for example, exposed silica fibers (e.g.,
515 in FIG. 5). These exposed silica fibers 515 may be silane
modified, for example, using the reaction scheme shown in FIG. 4.
That is, the exposed silica fibers may be post-exposure modified
using vinylbenzylethylenediaminepropyltrimethoxysilane
hydrochloride (CAS Number 171869-89-9) as the silane coupling
agent.
[0090] For example, the exposed silica fibers may be reacted with
Dow Corning.RTM. Z-6032 Silane, for example, using conventional
silane surface modification techniques well known to those skilled
in the art. Dow Corning.RTM. Z-6032 Silane contains
1,2-ethanediamine, N-[3-(trimethoxysilyl)propyl]-,
N'-[(ethylphenyl)methyl] derivatives, hydrochlorides (CAS Number
171869-89-9) (30-50%), along with methanol (50-70%) and
N-[3-(trimethoxysilyl)propyl]ethylenediamine (CAS Number 1760-24-3)
(10-20%). This reaction may be performed at room temperature using
conventional procedures well known to those skilled in the art. The
reaction conditions may be either acidic or basic. For example, the
reaction may be performed in an acid bath having a pH of
approximately 4.5. Either HCl or acetic acid, for example, may be
used to drop the pH to 4.5 or lower. Alternatively, the reaction
may be performed in a bath having a basic pH. In this case, a pH of
7-12 is preferred, most preferred is pH=10. Either ammonium or
sodium hydroxide, for example, may be used to raise the pH to 7 or
higher. In either case, the reaction is typically performed in the
presence of ethanol (or methanol) and water. Typically, methanol is
preferred for trimethoxysilanes, while ethanol is preferred for
triethoxysilanes.
[0091] Method 600 then continues by applying an epoxy-based resin
system formulation over at least a portion of the overcoat layer
and a second portion of the metal conductors (step 630). For
example, step 630 may correspond to applying an epoxy-based resin
system formulation that includes a latent functionality. The
epoxy-based resin system formulation may be applied using
conventional deposition processes well known to those skilled in
the art. In some embodiments, the epoxy-based resin system
composition includes one or more epoxy-based resins, one or more
hardeners and, optionally, one or more blowing agents and/or one or
more filler materials. An epoxide functionality of at least one of
the one or more epoxy-based resins and a reactive functionality of
at least one of the one or more hardeners may react with each other
at a first temperature. In some embodiments, it may be desirable to
initially cure the epoxy-based resin system formulation at the
first temperature. The latent functionality, which does not react
at the first temperature, is contained in at least one of the one
or more epoxy-based resins, the one or more hardeners and the one
or more filler materials and reacts in response to another stimulus
(e.g., UV light in conjunction with a UV initiator and/or a second
temperature greater than the first temperature) to enhance chemical
bonding between the overcoat layer and a protection layer (which
will be produced from this epoxy-based resin system
formulation).
[0092] Then, the method 600 continues by curing (and, optionally,
blowing), at a second temperature (and/or using UV light in
conjunction with a UV initiator), the epoxy-based resin system
composition to produce a protection layer (step 635). For example,
referring temporarily to FIGS. 1 and 2, step 635 may correspond to
curing an epoxy-based resin system formulation that includes a
latent functionality for polymer adhesion improvement to produce
the protection layer 121. At the second temperature (and/or in
response to UV light in conjunction with a UV initiator), as noted
above, the latent functionality reacts to enhance the chemical
bonding between the overcoat layer and the protection layer. In
embodiments where the epoxy-based resin system formulation includes
one or more blowing agents, curing the epoxy-based resin system
formulation also blows (foams) the epoxy-based resin system
formulation creating voids (e.g., 510 in FIG. 5) on the surface of
the protection layer.
[0093] Optionally, the cured protection layer may then be etched
(step 640). In this optional step, the cured protection layer may
be modified via an etching process in its entirety or locally in
one or more critical areas (e.g., regions where the various
platings of the side termination will be subsequently applied). The
etching process may be mechanical and/or chemical. For example, the
cured protection layer may be etched using a mechanical etching
process such as bead blasting or polishing. Such mechanical etching
processes are conventional and well known to those skilled in the
art. Alternatively, the cured protection layer may be etched using
a chemical etching process such as acid etching, alkaline etching,
permanganate etching, or gas plasma etching. Such chemical etching
processes are conventional and well known to those skilled in the
art. The etching process creates a rough surface (e.g., voids 510
in FIG. 5) on the surface of the cured protection layer.
[0094] Method 600 then continues by applying a silver layer of the
side termination structures over at least a portion of the
protection layer, and subsequently applying the remaining layers of
the side termination structures (step 645). For example, referring
temporarily to FIGS. 1 and 2, step 645 may correspond to applying
the silver (Ag) or Ag compound layer 112 over a first portion of
the protection layer 121, and subsequently applying the nickel (Ni)
or Ni compound layer 114 over the Ag or Ag compound layer, a second
portion of the protection layer 121 and a portion of the overcoat
layer 120, and finally applying the Tin (Sn) or Sn compound layer
116 (solder) over the Sn or Sn compound layer 114 and a portion of
the overcoat layer 120. These layers may be applied using
conventional deposition processes (e.g., a conventional electroless
plating bath and/or a conventional electrolytic deposition process)
well known to those skilled in the art.
[0095] In addition, a conformal coating (e.g., 130 in FIGS. 2 and
3) may be applied over the resulting peel-resistant ASR.
EXAMPLES (PROPHETIC)
Example 1
[0096] The following ingredients may be used at the specified
quantities to make an epoxy-based resin system
composition/formulation: [0097] Phenyl glycidyl ether [epoxy-based
resin]: 3.00 g [0098] Amino-ethylpiperazine [hardener]
(k.sub.rel=65.3): 0.50 g [0099] N,N'-Diethyl-1,2-ethanediamine
[hardener containing latent functionality] (k.sub.rel=20.3): 0.50 g
The following is an illustrative calculation of the stoichiometric
amount of amine hardener to use to make the epoxy-based resin
system composition/formulation used in Example 1. This calculation
is based on methodology well known to those skilled in the art. The
epoxy equivalent weight (sometimes referred to as "EEW" or "Epoxide
eq wt of resin") for phenyl glycidyl ether is 151. In general,
Amine H eq wt=MW of amine/number of active hydrogen.
Amino-ethylpiperazine has 3 active Hs, so Amine H eq wt=129.2/3=43.
In general, parts per hundred (phr) of amine=(Amine H eq
wt.times.100)/Epoxide eq wt of resin. Then the phr (parts per
hundred resin) amine becomes: (43*100)/151=28.5. Similarly, for the
latent amine, there are 2 active Hs, so the latent amine H eq
wt=116.2/2=58.1. For the latent amine, the phr amine is
(58.1*100)/151=38.5. So for every 100 parts (this could be in
grams) of epoxy, we would add 28.5 parts of amino-ethylpiperazine
or 38.5 parts of the diamine for stoichiometric cure. Since we want
to have residual epoxy functionality to react with the latent
amine, we would limit the phr of amino-ethylpiperazine. For
simplicity sake, we could add 14.25 g of amino-ethylpiperazine to
100 g of phenyl glycidyl ether and have 50% of the epoxy
functionality remaining which we would then react with 19.25 g of
the diamine latent hardener.
[0100] The procedure for preparation of the epoxy-based resin
system composition (for producing an overcoat layer for an ASR) is
as follows: The phenyl glycidyl ether is weighed out in a mixing
container at room temperature. The amino-ethylpiperazine is weighed
out in the mixing container at room temperature. The
N,N'-diethyl-1,2-ethanediamine is weighed out in the mixing
container at room temperature. The contents of the mixing container
are then mixed thoroughly with a spatula for about 2 minutes. After
mixing, a sufficient amount of the epoxy-based resin system
composition is deposited on a portion of the resistor element and a
first portion of the Ag layer of the upper termination of the ASR.
The epoxy-based resin system composition is placed into a
50.degree. C. oven to cure (initial cure/cross-linking) for 8 hours
to produce the initially cured overcoat layer.
[0101] Next, the procedure for preparation of the epoxy-based resin
system formulation (for producing a protection layer of an ASR) is
as follows: The phenyl glycidyl ether is weighed out in a mixing
container at room temperature. The amino-ethylpiperazine is weighed
out in the mixing container at room temperature. The
N,N'-Diethyl-1,2-ethanediamine is weighed out in the mixing
container at room temperature. The contents of the mixing container
are then mixed thoroughly with a spatula for about 2 minutes. After
mixing, a sufficient amount of the epoxy-based resin system
formulation is deposited on a second portion of the Ag layer of the
upper termination of the ASR and a portion of the initially cured
overcoat layer. The epoxy-based resin system formulation is placed
into a 50.degree. C. oven to cure (initial cure/cross-linking) for
8 hours to produce the initially cured protection layer. The
initially cured overcoat layer and the initially cured protection
layer are then placed into a 100.degree. C. oven to cure (final
cure/cross-linking) for 4 hours to produce the finally cured
overcoat layer/protection layer.
Example 2
[0102] The following ingredients may be used at the specified
quantities to make an epoxy-based resin system
composition/formulation: [0103] N,N-Diglycidyl-4-glycidyloxyaniline
[epoxy-based resin]: 2.50 g [0104] Diglycidyl
1,2-cyclohexanedicarboxylate [epoxy-based resin containing latent
functionality]: 0.50 g [0105] Methyltetrahydrophthalic anhydride
(MTHPA) [hardener]: 1.00 g
[0106] The following is an illustrative calculation of the
stoichiometric amount of amine hardener to use to make the
epoxy-based resin system composition/formulation used in Example 2.
This calculation is based methodology that is well known to those
skilled in the art. The epoxy equivalent weight (sometimes referred
to as "EEW" or "Epoxide eq wt of resin") for both epoxies are
roughly 105 g/eq for glycidyloxyaniline and 165 g/eq (from the
center of the range) for the latent epoxy. The formula weight for
the anhydride is 166.2 g/mole (or g/eq as this is a monofunctional
anhydride). Consequently, we have to determine ratios based on
equivalents. So, for 105 parts of the glycidyl epoxy, we have 1 eq
and need 1 eq (166.2 g) of the anhydride to cure it
stoichiometrically. Since we want to have latent epoxy
functionality, we would use less glycidyl epoxy (52.5 parts or
grams would leave 50% of the anhydride available to cure the
cycloaliphatic epoxy). In this example, we would have 83.1 grams of
residual anhydride left to react with the latent epoxy. Based on
equivalents, we have 0.5 eqs of anhydride left to react with the
latent epoxy. To cure it stoichiometrically, we then need 0.5 eqs
of latent epoxy or (0.5 eq*165 g/eq)=82.5 g of latent epoxy.
[0107] The procedure for preparation of the epoxy-based resin
system composition (for producing an overcoat layer for an ASR) is
as follows: The N,N-diglycidyl-4-glycidyloxyaniline is weighed out
in a mixing container at room temperature. The diglycidyl
1,2-cyclohexanedicarboxylate is weighed out in the mixing container
at room temperature. The contents of the mixing container are then
mixed thoroughly with a spatula for about 2 minutes. The
methyltetrahydrophthalic anhydride is weighed out in the mixing
container at room temperature. The contents of the mixing container
are then mixed thoroughly with a spatula for about 2 minutes. After
mixing, a sufficient amount of the epoxy-based resin system
composition is deposited on a portion of the resistor element and a
first portion of the Ag layer of the upper termination of the ASR.
The epoxy-based resin system composition is placed into a
130.degree. C. oven to cure (initial cure/cross-linking) for 2
hours to produce the initially cured overcoat layer.
[0108] Next, the procedure for preparation of the epoxy-based resin
system formulation (for producing a protection layer of an ASR) is
as follows: The N,N-diglycidyl-4-glycidyloxyaniline is weighed out
in a mixing container at room temperature. The diglycidyl
1,2-cyclohexanedicarboxylate is weighed out in the mixing container
at room temperature. The contents of the mixing container are then
mixed thoroughly with a spatula for about 2 minutes. The
methyltetrahydrophthalic anhydride is weighed out in the mixing
container at room temperature. The contents of the mixing container
are then mixed thoroughly with a spatula for about 2 minutes. After
mixing, a sufficient amount of the epoxy-based resin system
formulation is deposited on a second portion of the Ag layer of the
upper termination of the ASR and a portion of the initially cured
overcoat layer. The epoxy-based resin system formulation is placed
into a 130.degree. C. oven to cure (initial cure/cross-linking) for
2 hours to produce the initially cured protection layer. The
initially cured overcoat layer and the initially cured protection
layer are then placed into a 180.degree. C. oven to cure (final
cure/cross-linking) for 1.5 hours to produce the finally cured
overcoat layer/protection layer.
Example 3
[0109] The following ingredients may be used at the specified
quantities to make an epoxy-based resin system
composition/formulation:
[0110] N,N-Diglycidyl-4-glycidyloxyaniline [epoxy-based resin]:
3.00 g
[0111] Methyltetrahydrophthalic anhydride (MTHPA) [hardener]: 1.00
g
[0112] Modified silica fibers [filler material containing latent
functionality]: 0.150 g
The following is an illustrative calculation of the stoichiometric
amount of amine hardener to use to make the epoxy-based resin
system composition/formulation used in Example 3. This calculation
is based on methodology well known to those skilled in the art. The
epoxy equivalent weight (sometimes referred to as "EEW" or "Epoxide
eq wt of resin") for the glycidyl epoxy is roughly 105 g/eq. The
formula weight for the anhydride is 166.2 g/mole (or g/eq as this
is a monofunctional anhydride). Consequently, we have to determine
ratios based on equivalents. So, for 105 parts of the glycidyl
epoxy, we have 1 eq and need 1 eq (166.2 g) of the anhydride to
cure it stoichiometrically. So, in this illustrative calculation,
we have 105 parts of epoxy, 166 parts anhydride, and 5.25 parts
fibers.
[0113] Initially, the procedure for preparation of the modified
silica fibers is as follows: Silica fibers are reacted with Dow
Corning.RTM. Z-6032 Silane using the conventional procedures
described above with reference to FIG. 4.
[0114] The procedure for preparation of the epoxy-based resin
system composition (for producing an overcoat layer for an ASR) is
as follows: The N,N-diglycidyl-4-glycidyloxyaniline is weighed out
in a mixing container at room temperature. The modified silica
fibers are weighed out in the mixing container at room temperature.
The contents of the mixing container are then mixed thoroughly with
a spatula for about 2 minutes. The methyltetrahydrophthalic
anhydride is weighed out in the mixing container at room
temperature. The contents of the mixing container are then mixed
thoroughly with a spatula for about 2 minutes. After mixing, a
sufficient amount of the epoxy-based resin system composition is
deposited on a portion of the resistor element and a first portion
of the Ag layer of the upper termination of the ASR. The
epoxy-based resin system composition is placed into a 130.degree.
C. oven to cure (initial cure/cross-linking) for 2 hours to produce
the initially cured overcoat layer.
[0115] The initially cured overcoat layer is then etched to expose
the modified silica fibers. This may be accomplished using a
mechanical etching process (e.g., bead blasting or polishing) or a
chemical etching process (e.g., acid etching, alkaline etching,
permanganate etching, or gas plasma etching).
[0116] Next, the procedure for preparation of the epoxy-based resin
system formulation (for producing a protection layer of an ASR) is
as follows: The N,N-diglycidyl-4-glycidyloxyaniline is weighed out
in a mixing container at room temperature. The modified silica
fibers are weighed out in the mixing container at room temperature.
The contents of the mixing container are then mixed thoroughly with
a spatula for about 2 minutes. The methyltetrahydrophthalic
anhydride is weighed out in the mixing container at room
temperature. The contents of the mixing container are then mixed
thoroughly with a spatula for about 2 minutes. After mixing, a
sufficient amount of the epoxy-based resin system formulation is
deposited on a second portion of the Ag layer of the upper
termination of the ASR and a portion of the initially cured/etched
overcoat layer. The epoxy-based resin system formulation is placed
into a 130.degree. C. oven to cure (initial cure/cross-linking) for
2 hours to produce the initially cured protection layer. The
initially cured overcoat layer and the initially cured protection
layer are then placed into a 180.degree. C. oven to cure (final
cure/cross-linking) for 1.5 hours to produce the finally cured
overcoat layer/protection layer.
Example 4
[0117] The following ingredients may be used at the specified
quantities to make an epoxy-based resin system
composition/formulation:
[0118] N,N-Diglycidyl-4-glycidyloxyaniline [epoxy-based resin]:
3.00 g
[0119] Methyltetrahydrophthalic anhydride (MTHPA) [hardener]: 1.00
g
[0120] Modified silica fibers [filler material containing latent
functionality]: 0.15 g
[0121] CELOGEN OT blowing agent (CelChem LLC): 0.25 g
[0122] DC-193 surfactant (Air Products & Chemical Corporation):
0.10 g
The following is an illustrative calculation of the stoichiometric
amount of amine hardener to use to make the epoxy-based resin
system composition/formulation used in Example 4. This calculation
is based on methodology well known to those skilled in the art. The
epoxy equivalent weight (sometimes referred to as "EEW" or "Epoxide
eq wt of resin") for the glycidyl epoxy is roughly 105 g/eq. The
formula weight for the anhydride is 166.2 g/mole (or g/eq as this
is a monofunctional anhydride). Consequently, we have to determine
ratios based on equivalents. So, for 105 parts of the glycidyl
epoxy, we have 1 eq and need 1 eq (166.2 g) of the anhydride to
cure it stoichiometrically. So, in this illustrative calculation,
we have 105 parts of epoxy, 166 parts anhydride, 5.25 parts fibers,
8.75 parts blowing agent, and 3.5 parts surfactant.
[0123] Initially, the procedure for preparation of the modified
silica fibers is as follows: Silica fibers are reacted with Dow
Corning.RTM. Z-6032 Silane using the conventional procedures
described above with reference to FIG. 4.
[0124] The procedure for preparation of the epoxy-based resin
system composition (for producing an overcoat layer for an ASR) is
as follows: The N,N-diglycidyl-4-glycidyloxyaniline is weighed out
in a mixing container at room temperature. The DC-193 surfactant is
weighed out in the mixing container at room temperature. The
modified silica fibers are weighed out in the mixing container at
room temperature. The contents of the mixing container are then
mixed thoroughly with a spatula for about 2 minutes. The CELOGEN OT
blowing agent is added to the contents of the mixing container and
stirred together. The methyltetrahydrophthalic anhydride is weighed
out in the mixing container at room temperature. The contents of
the mixing container are then mixed thoroughly with a spatula for
about 2 minutes. After mixing, a sufficient amount of the
epoxy-based resin system composition is deposited on a portion of
the resistor element and a first portion of the Ag layer of the
upper termination of the ASR. The epoxy-based resin system
composition is placed into a 130.degree. C. oven to cure (initial
cure/cross-linking) and foam/blow for 2 hours to produce the
initially cured/blown overcoat layer. The modified silica particles
are exposed in the voids on the surface of the blown (foamed)
epoxy.
[0125] Next, the procedure for preparation of the epoxy-based resin
system formulation (for producing a protection layer of an ASR) is
as follows: The N,N-diglycidyl-4-glycidyloxyaniline is weighed out
in a mixing container at room temperature. The DC-193 surfactant is
weighed out in the mixing container at room temperature. The
modified silica fibers are weighed out in the mixing container at
room temperature. The contents of the mixing container are then
mixed thoroughly with a spatula for about 2 minutes. The CELOGEN OT
blowing agent is added to the contents of the mixing container and
stirred together. The methyltetrahydrophthalic anhydride is weighed
out in the mixing container at room temperature. The contents of
the mixing container are then mixed thoroughly with a spatula for
about 2 minutes. After mixing, a sufficient amount of the
epoxy-based resin system formulation is weigh out and deposited on
a second portion of the Ag layer of the upper termination of the
ASR and a portion of the initially cured/blown overcoat layer. The
epoxy-based resin system formulation is placed into a 130.degree.
C. oven to cure (initial cure/cross-linking) and foam/blow for 2
hours to produce the initially cured/blown protection layer. The
initially cured/blown overcoat layer and the initially cured/blown
protection layer are then placed into a 180.degree. C. oven to cure
(final cure/cross-linking) for 1.5 hours to produce the finally
cured overcoat layer/protection layer.
[0126] The above-listed exemplary epoxy-based resins, hardeners,
filler materials, blowing agents, surfactants and concentrations
are set forth for the purpose of illustration, not limitation.
Those skilled in the art will appreciate that other resins,
hardeners, filler materials, blowing agents, surfactants, curing
conditions, and/or concentrations may be used within the scope of
the present invention.
[0127] One skilled in the art will appreciate that many variations
are possible within the scope of the present invention. Thus, while
the present invention has been particularly shown and described
with reference to some embodiments thereof, it will be understood
by those skilled in the art that these and other changes in form
and detail may be made therein without departing from the spirit
and scope of the present invention.
* * * * *