U.S. patent application number 10/155027 was filed with the patent office on 2003-04-17 for method for manufacturing solder mask of printed circuit board.
This patent application is currently assigned to S&S Technology Corporation. Invention is credited to Chih, Wan-Kuo, Maa, Chong-Ren, Tsai, Ming-Sung.
Application Number | 20030071014 10/155027 |
Document ID | / |
Family ID | 25522504 |
Filed Date | 2003-04-17 |
United States Patent
Application |
20030071014 |
Kind Code |
A1 |
Maa, Chong-Ren ; et
al. |
April 17, 2003 |
Method for manufacturing solder mask of printed circuit board
Abstract
A solder mask manufacturing method adapted to apply a solder
mask on a surface of a substrate of a circuit board, said surface
is provided with a conductor pattern having an unsheltered portion
and a sheltered portion which is covered by said solder mask. The
method comprises the steps of: a) disposing a layer of semi-solid
solder mask material having an expansion coefficient substantially
the same as that of the substrate on the surface of said substrate
to cover said copper conductor pattern, and a metal foil covering
the material layer; b) applying pressure to the metal foil and
applying baking treatment to cure the solder mask material in to
solid; c) utilizing chemical solution and plasma etching to remove
the metal foil and the solid solder mask material above the
unsheltered portion of said copper conductor pattern respectively
such that the unsheltered portion can be exposed; and d) using
chemical solution to remove the residual metal foil.
Inventors: |
Maa, Chong-Ren; (Taipei,
TW) ; Chih, Wan-Kuo; (Hsinchu, TW) ; Tsai,
Ming-Sung; (Keelung, TW) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.
624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Assignee: |
S&S Technology
Corporation
Taoyaun
TW
|
Family ID: |
25522504 |
Appl. No.: |
10/155027 |
Filed: |
May 28, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10155027 |
May 28, 2002 |
|
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09974908 |
Oct 12, 2001 |
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6395625 |
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Current U.S.
Class: |
216/27 ; 216/83;
257/E23.062; 257/E23.069; 257/E23.077 |
Current CPC
Class: |
H05K 2203/0152 20130101;
Y10T 29/49126 20150115; Y10T 29/49149 20150115; Y10T 29/49155
20150115; H05K 2201/0191 20130101; Y10T 29/49144 20150115; H01L
23/49822 20130101; H05K 2201/0959 20130101; H05K 3/0094 20130101;
H05K 2203/066 20130101; H01L 2924/0002 20130101; Y10T 29/49151
20150115; H01L 23/49816 20130101; H05K 2203/1152 20130101; Y10T
29/49156 20150115; H05K 2203/0376 20130101; H01L 23/49894 20130101;
H05K 3/28 20130101; H01L 2924/0002 20130101; H05K 2203/0554
20130101; Y10T 29/49147 20150115; H05K 3/0041 20130101; H01L
2924/00 20130101; Y10T 428/24917 20150115 |
Class at
Publication: |
216/27 ;
216/83 |
International
Class: |
C03C 015/00; B44C
001/22 |
Claims
What is claimed is:
1. A solder mask manufacturing method of a printed circuit board
adapted to apply a solder mask on a surface of a substrate of the
printed circuit board, wherein the surface of the substrate is
provided with a conductor pattern having an unsheltered portion and
a sheltered portion being covered by said solder mask, the
manufacturing method comprising the following steps: (a) coating a
layer of semi-solid solder mask material, which is pre-coated on
one side of a metal foil, on the surface of the substrate such that
the sheltered and unsheltered portions of said conductor pattern
are covered by said solder mask material layer, said solder mask
material having a thermal expansion coefficient substantially
identical to that of the substrate of said printed circuit board;
(b) pressing said metal foil and curing said semi-solid solder mask
material layer into solid such that said solder mask material layer
firmly covers the surface of the substrate; (c) covering a
photo-resist layer on the other side of the metal foil; (d)
photoimaging positions of the photo-resist layer; (e) removing the
photo-resist layer and the metal foil corresponding in location
above the unsheltered portion of said conductor pattern for
exposing the solder mask material layer above the unsheltered
portion of said conductor pattern to outside; (f) removing the
residual photo-resist layer; (g) removing the solder mask material
layer above the unsheltered portion of said conductor pattern such
that said unsheltered portion can be exposed outside; (h) removing
the residual metal foil.
2. The manufacturing method as defined in claim 1, wherein the
substrate of said printed circuit board is made of a material
containing a resin, and said semi-solid solder mask material in the
step (a) is made of a material containing a resin which is
substantially identical to the resin of the substrate.
3. The manufacturing method as defined in claim 2, wherein the
resin contained in the substrate of said printed circuit board is
epoxy resin.
4. The manufacturing method as claimed in claim 1, wherein the
thickness of the metal foil is between 20 m.about.40 m.
5. The manufacturing method as claimed in claim 1, wherein the
pre-coated semi-solid solder mask material has a thickness of about
30 m .about.100 m in the step (a).
6. The manufacturing method as claimed in claim 1, wherein the
pressure applied on the metal foil in the step (b) is between
10.about.40 kgw/cm.sup.2.
7. The manufacturing method as defined in claim 1, wherein the
metal foil is removed by chemical solution etching in the step
(e).
8. The manufacturing method as defined in claim 7, wherein the
chemical solution used to remove the metal foil in the step (e) is
ferric chloride (FeCl.sub.3) solution.
9. The manufacturing method as defined in claim 1, wherein the
residual photo-resist is remove by using sodium hydroxide (NaOH)
solution in the step (f).
10. The manufacturing method as defined in claim 1, wherein the
solder mask material layer above the unsheltered portion of said
conductor pattern is removed by plasma etching in the step (g).
11. The manufacturing method as defined in claim 1, wherein the
residual metal foil is removed by chemical solution etching in the
step (h).
12. The manufacturing method as defined in claim 11, wherein the
chemical solution used to remove the residual metal foil is
phosphoric acid (H.sub.3PO.sub.4) solution.
13. The manufacturing method as defined in claim 11, wherein the
chemical solution used to remove the residual metal foil is
hydrochloric acid (HCl) solution.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a method for
manufacturing a printed circuit board (PCB), and more particularly
to a method for manufacturing the solder mask of the printed
circuit board.
BACKGROUND OF THE INVENTION
[0002] In the manufacture of a conventional printed circuit board,
after forming the outer layer conductor pattern, a solder mask
protective treatment has to be applied to the conductor pattern so
as to prevent oxidation of the conductor pattern or solder
connection short circuit.
[0003] In a solder mask manufacturing process for the conventional
printed circuit board, a solder mask paint is applied to the
surface of the circuit board by halftone printing, roller type
coating, screen coating or electrostatic spray coating, etc. After
pre-baking, drying and cooling, exposure is employed to display
images. The method of imaging removes unnecessary paint, and the
resin in the remaining paint is completely cured by
high-temperature baking in the final step to form a solder mask
covered on the surface of the PCB to protect the conductor
pattern.
[0004] The conventional solder mask manufacturing process has the
following disadvantages:
[0005] 1. Using halftone printing or roller type coating to apply
the solder mask paint to the printed circuit board requires
multiple halftone printing or roller printing steps in order to
accumulate the paint to the desired thickness, which is
complicated.
[0006] 2. During the process of baking the printing circuit board
at high temperature, since the resin material in the solder mask
paint has an expansion coefficient different from that of the
circuit board substrate, internal stress will form between the
resin material and the circuit board to cause the bend of the
printed circuit board.
[0007] 3. The thickness of the solder mask paint layer is not easy
to control, resulting in electric instability of the circuit
board.
[0008] 4. Air bubbles can easily get in during the process of
coating the solder mask paint to result in poor reliability quality
of the solder mask and shortened life of the solder mask layer.
[0009] 5. Coating the circuit board with solder mask paint cannot
fill through holes in the circuit board with solder mask paint.
Therefore, before coating, insulating fillers are disposed in the
through holes respectively and are ground flat before coating the
solder mask paint, thereby increasing manufacturing time and cost
of the printing circuit board.
[0010] 6. When coating the circuit board with solder mask paint,
coating layer cannot be easily formed on the copper foil conductor
pattern, and the bonding therebetween is relatively poor.
SUMMARY OF THE INVENTION
[0011] The primary object of the present invention is to provide a
solder mask manufacturing method for a printed circuit board that
has good quality and that will not cause bend of the circuit
board.
[0012] In order to achieve the aforesaid object, the present
invention is to provide a solder mask manufacturing method adapted
to apply a solder mask on a surface of a substrate of a circuit
board, said surface is provided with a conductor pattern having an
unsheltered portion and a sheltered portion which is covered by
said solder mask. The method comprises the steps of: disposing a
layer of semi-solid solder mask resin material having an expansion
coefficient substantially the same as that of the substrate on the
surface of said substrate to cover said copper conductor pattern,
and a metal foil for covering the resin material layer; applying
predetermined pressure to the metal foil and baking at a
predetermined temperature for a predetermined time to cure the
semi-solid solder mask resin material; utilizing chemical solution
etching to remove the metal foil above the unsheltered portion of
said copper conductor pattern, and using plasma etching to remove
the solid solder mask material above said unsheltered portion of
said conductor pattern such that the unsheltered portion of the
said conductor pattern can be exposed; and lastly, using chemical
solution to remove the residual metal foil.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a flow chart of a preferred embodiment of the
present invention; and
[0014] FIG. 2 is a schematic view of the preferred embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Referring to FIG. 1, the solder mask manufacturing method
for a printed circuit board of the present invention adapted to
apply a solder mask on a surface of a substrate of the printed
circuit board, said surface of the substrate is provided with a
cooper conductor pattern having an unsheltered portion and a
sheltered portion which is covered by said solder mask. The method
includes the following steps:
[0016] 1. Coating of solder mask resin material: disposing a layer
of semi-solid solder mask resin material of a predetermined
thickness and expansion coefficient identical or similar to that of
the circuit board substrate on the surface of the substrate such
that the cooper conductor pattern is covered by said resin
material, and then a metal foil of a predetermined thickness is
disposed to cover the solder mask resin material.
[0017] 2. Press bonding and curing of solder mask resin material:
applying predetermined pressure to the metal foil such that solder
mask resin material between the metal foil and the substrate of the
printed circuit board tightly covers the surface of the substrate,
and then baking treatment is applied at a predetermined temperature
for a predetermined time to cure the semi-solid solder mask resin
material.
[0018] 3. Removing unnecessary solder mask material: utilizing
chemical solution etching to remove the metal foil above the
unsheltered portion of the cooper conductor pattern, and then using
plasma etching to remove the solder mask resin material above the
unsheltered portion of the cooper conductor pattern such that said
unsheltered portion of the copper unsheltered portion can be
exposed.
[0019] 4. Removal of metal foil: using chemical solution to remove
the residual metal foil covering the solder mask material, thereby
completing the manufacturing of the solder mask.
[0020] The aforesaid is the steps of the process of this invention.
Hereinafter, the invention is described in detail using a preferred
embodiment with reference to FIG. 2.
[0021] Referring to FIG. 2, in the solder mask manufacturing
process for a printed circuit board of this invention, a printed
circuit board 1 which has undergone the steps of hole drilling and
plating, and outer layer cooper conductor pattern circuit layout is
subjected to solder mask treatment of the outer layer conductor
pattern of the circuit board 1. The material of the substrate 11 of
the printed circuit board 1 is multi-function epoxy resin.
Therefore, in this embodiment, the printed circuit board 1 has a
plurality of through holes 12 and predetermined outer layer copper
conductor pattern 13 (see FIG. 2A). The cooper conductor pattern 13
can be defined into two portions, namely, the unsheltered portion
13a and the sheltered portion. The solder mask manufacturing
process for the printed circuit board 1 is as follows:
[0022] 1. Coating of solder mask material:
[0023] Firstly, prepare a aluminum foil 2 with a thickness between
20 .mu.m .about.40 .mu.m. Apply solder mask resin material 3 of a
thickness between 30 .mu.m .about.100 .mu.m to one side of the
aluminum foil 2. The solder mask material is made of multifunction
epoxy resin paint identical to that of the substrate 11 of the
printed circuit board 1 with organic solution added, and is
pre-baked to form a semi-solid state (i.e. thick and sticky). Cover
the side of the circuit board 1 that is to be solder mask treated
with the solder mask resin material on the aluminum foil 2 so that
the solder mask material 3 is sandwiched between the substrate 11
of the circuit board 1 and the aluminum foil 2 (see FIG. 2B).
[0024] 2. Press bonding and curing of solder mask material:
[0025] Apply uniform force of 10.about.40 kgw/cm.sup.2 to the
aluminum foil 2, and bake the solder mask material 3 at a
temperature of 185.degree. C. for 1.5 hours to 3 hours such
that:
[0026] a) The solder mask material 3 fills through holes 12 and
micro-pores such as blind holes in the substrate 11 of the circuit
board 1 due to pressure applied and tightly covers the substrate 11
to form a cover layer.
[0027] b) Organic solution in the solder mask material 3 evaporates
when heated, and epoxy resin in the solder mask material 3
gradually cures to form a solder mask protective layer.
[0028] After curing of epoxy resin in the solder mask material 3 to
form a solder mask protective layer, release the pressure and
temperature applied.
[0029] 3. Removal of unnecessary solder mask material:
[0030] Press a dry film photo-resist 4 on the aluminum foil 2 with
suitable temperature and pressure (as shown in FIG. 2C), and
subject the dry film photo-resist 4 to light exposure in
conjunction with a negative film so that the dry film photo-resist
4 generates images relative to positions of the sheltered portion
of the cooper conductor pattern 13. Etch the parts of the dry film
4a without images and the aluminum foil 2a using carbonic acid and
ferric chloride (FeCl.sub.3) solution with specific gravity
1.3.about.1.5 and temperature of 40.degree. C..about.60.degree. C.
so that epoxy resin solder mask layer at where the aluminum foil
was removed is exposed on the outside (as shown in FIG. 2D), and
then remove the residual dry film 4 using sodium hydroxide of
1.about.3 wt % and temperature of 45.degree. C..about.65.degree.
C.
[0031] Subsequently, plasma etching is used to remove the exposed
epoxy resin solder mask layer so that the unsheltered portion 13a
of the cooper conductor pattern is exposed on the substrate 11 (as
shown in FIG. 2E).
[0032] 4. Removal of metal foil:
[0033] Lastly, use phosphoric acid (H.sub.3PO.sub.4) solution of
60%.about.80% volume to volume and temperature of 50.degree.
C..about.80.degree. C., or hydrochloric acid (HCl) with
concentration of 10%.about.40% and temperature of 20.degree.
C..about.40.degree. C. to remove the residual aluminum foil 2 (as
shown in FIG. 2F), completing the entire solder mask manufacturing
process. The printed circuit board 1 can subsequently undergo
nickel-plating operation of the unsheltered portion 13a of the
cooper conductor pattern 13. Since phosphoric acid or hydrochloric
acid can corrode aluminum and will not corrode copper severely,
this is the reason why this embodiment selects aluminum foil as
cover layer of the solder mask material.
[0034] As techniques relating to pressing the dry film, light
exposure, imaging and plasma etching are known art, it is not
necessary to further describe the same herein.
[0035] Hereinafter, the advantages of the embodiment are set forth
as follows:
[0036] 1. The thickness of the solder mask 3 can be set at one time
to reduce process step so as to reduce process costs.
[0037] 2. Since the solder mask 3 and substrate 11 of the circuit
board 1 are of the same multifunction epoxy resin, the expansion
coefficient thereof is the same as that of substrate 11 of the
circuit board 1. Therefore, during the process of baking in step 2,
internal stress will not be present between the solder mask 3 and
the substrate 11 so as not to cause bend of the circuit board 1.
Particularly, application of uniform force to the substrate 11
during the process of baking in step 2 will prevent deformation of
the circuit board 1.
[0038] 3. As the solder mask material 3 is attached to the
substrate 11, it is subjected to an uniform force via the aluminum
foil 2 for a period of time, the solder mask material 3 will cover
the circuit board 1 with uniform thickness and forms a solder mask
protective layer with uniform thickness after curing so that the
circuit board 1 has stable electric characteristics.
[0039] 4. As the solder mask material 3 is attached to the
substrate 11, it is subjected to an uniform force via the aluminum
foil 2 until cured, air bubbles will not get thereinto during that
period of time and can therefore enhance quality of the solder mask
protective layer and prolong the life thereof.
[0040] 5. Due to the pressure applied, the solder mask material 3
can fill through holes and micro-pores such as blind holes in the
substrate 11 simultaneously. Therefore, it is not necessary to fill
the through holes with insulating filler material and grind the
same even prior to solder mask of the circuit board 1, thereby
reducing manufacturing time and costs of the printed circuit
board.
[0041] 6. As the solder mask material 3 is caused to cover the
surface of the substrate 11 by applying pressure and heating,
copper conductor pattern 13 on the substrate 11 can easily attach
thereto and will not detach therefrom.
[0042] Although the present invention has been illustrated and
described with reference to the preferred embodiment thereof, it
should be understood that it is in no way limited to the details of
such embodiment but is capable of numerous modifications within the
scope of the appended claims.
* * * * *