U.S. patent application number 10/960116 was filed with the patent office on 2005-04-14 for pb-free solder alloy, and solder material and solder joint using same.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Ochi, Shinya, Tawara, Fumitoshi.
Application Number | 20050079092 10/960116 |
Document ID | / |
Family ID | 34425378 |
Filed Date | 2005-04-14 |
United States Patent
Application |
20050079092 |
Kind Code |
A1 |
Ochi, Shinya ; et
al. |
April 14, 2005 |
Pb-free solder alloy, and solder material and solder joint using
same
Abstract
A solder alloy based on an Sn--Zn--In--Ag system contains, in
weight, 3.0%<Zn<5.0%, 0.1%<In<4.0%, 0.1%<Ag<0.4%,
and the balance Sn. Therefore, the current Sn--Pb soldering method
can be employed as it is. Further, a Pb-free solder material having
a solder characteristic with excellent bonding strengths of the
parts can be provided. Still further, since a difference between a
solidus temperature and a liquidus temperature is small, floating
of the parts leads can be suppressed, even in case where packaging
processes are performed many times over. Still further, when the
joint is exposed to the high temperature and high humidity
atmosphere, the bonding strength can be prevented from being
lowered.
Inventors: |
Ochi, Shinya; (Ehime,
JP) ; Tawara, Fumitoshi; (Ehime, JP) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
Osaka
JP
|
Family ID: |
34425378 |
Appl. No.: |
10/960116 |
Filed: |
October 8, 2004 |
Current U.S.
Class: |
420/557 |
Current CPC
Class: |
B23K 35/262 20130101;
C22C 13/00 20130101 |
Class at
Publication: |
420/557 |
International
Class: |
C22C 013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2003 |
JP |
2003-352015 |
Jul 30, 2004 |
JP |
2004-223189 |
Claims
What is claimed is:
1. A solder alloy based on an Sn--Zn--In--Ag system, the solder
alloy comprising, in weight: 3.0%<Zn<5.0%;
0.1%.ltoreq.In.ltoreq.4.0%; 0.1%.ltoreq.Ag.ltoreq.0.4%; and the
balance Sn.
2. A Pb-free solder material comprising a solder alloy and a flux,
wherein the solder alloy is based on an Sn--Zn--In--Ag system
having, in weight: 3.0%<Zn<5.0%; 0.1%.ltoreq.In.ltoreq.4.0%;
0.1%.ltoreq.Ag.ltoreq.0.4- %; and the balance Sn.
3. A solder alloy based on an Sn--Zn--In--Ag system and having at
least one element selected from the group consisting of Ni, Ti, Mg,
Al, and Co, the solder alloy comprising, in weight:
3.0%<Zn<5.0%; 0.1%.ltoreq.In.ltoreq.4.0%; and
0.1%.ltoreq.Ag.ltoreq.0.4%, wherein a total concentration of said
at least one element is in the range from about 0.001% to about
0.05% in weight, and the remaining portion thereof is Sn.
4. A Pb-free solder material comprising a solder alloy and a flux,
wherein the solder alloy has at least one element selected from a
group consisting of Ni, Ti, Mg, Al, and Co, based on an
Sn--Zn--In--Ag based solder alloy having: 3.0%<Zn<5.0%;
0.1%.ltoreq.In.ltoreq.4.0%; and 0.1%.ltoreq.Ag.ltoreq.0.4%, wherein
a total concentration of said at least one element is in the range
from about 0.001 to about 0.05% in weight and the remaining portion
thereof is Sn.
5. A solder joint of electrical and electronic equipment comprising
the solder alloy of claim 1.
6. A solder joint of electrical and electronic equipment comprising
the solder alloy of claim 3.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a Pb-free solder alloy, and
a solder material and a solder joint using same.
BACKGROUND OF THE INVENTION
[0002] Recently, the problem of the toxicity of lead (Pb) has
invoked a strong movement in regulating the disposal of lead to an
environment. Thus, as a bonding material for parts of electronic
products, a Pb-free solder has been substituted for a conventional
Sn--Pb solder.
[0003] As for characteristic properties of an alloy necessary as a
solder material, there are melting temperature, tensile strength,
ductility (or elongation property), wettability, bonding strengths
of parts joints, and the like.
[0004] A melting temperature of a solder is preferably to be set at
approximately 200.degree. C. If a melting point of the solder is
too high, it will exceed heat resistance temperatures of the parts
in a reflow soldering, whereby a current soldering method may
possibly incur damages on the parts. On the other hand, if a
melting point of the solder is too low, the solder becomes most
likely melted such that the parts may fall down or be peeled off in
case when the environmental temperature surrounding the parts
becomes high.
[0005] As a solder for a reflow soldering, in which a lead is
employed, there is an Sn-37Pb solder alloy, typically.
Alternatively, following Pb-free solder alloys have been studied.
For example, enumerated are Sn--Ag(--Cu) based, Sn--Cu(--Ni) based,
Sn--Ag--Bi--Cu based, Sn--Zn(--Bi,--Al) based, Sn--In--Ag--Bi based
solder alloys, and the like.
[0006] These are referred to as group I. Out of these, Sn--Ag(--Cu)
based, Sn--Cu(--Ni) based, and Sn--Bi--Cu based solder alloys have
alloy compositions whose melting points are measured in a range
from 210.degree. C. to 230.degree. C. and are used for a flow
soldering, a reflow soldering method, or the like. However, the
melting points of these alloys are higher than that of a
conventional Sn--Pb solder by 30.degree. C. to 40.degree. C. As a
result, under a temperature condition of reflow soldering by using
these alloys, the melting points thereof may exceed heat resistance
temperatures of the parts. It is technically difficult to increase
heat resistances of corresponding parts up to a temperature where
reflow soldering can be performed by using the aforementioned
solder. Meanwhile, Sn--Zn(--Bi,--Al) based and Sn--In--Ag--Bi based
solder alloys, and the like (referred to as group II), are employed
in a field of PCB (printed circuit board) packaging in which a
reflow soldering method is generally adopted. However, group II
alloys are highly oxidized in a melting state in the air, and
technically difficult to be applied in the flow soldering method at
this point. While a group II alloy has many disadvantages as a
solder in comparison with group I, it is advantageous in that its
melting point can be adjusted to a temperature region close to that
of the conventional Sn--Pb solder. Further, a group II alloy is
used by adjusting composition thereof such that melting point
thereof falls in the range from approximately 180.degree. C. to
210.degree. C.
[0007] Namely, the Sn--Zn(--Bi,--Al) based solder alloy can be used
under the current reflow soldering condition since a melting point
is in the range from approximately 190.degree. C. to 200.degree. C.
that is close to that of the conventional Sn-37Pb solder alloy, and
is advantageous in being of low cost among Pb-free solders.
However, it has been considered that wettability to a joint base
material of a solder is not good. Further, it has been confirmed
that bonding strengths of the parts are significantly deteriorated
if the joint to be soldered with a Cu base material is exposed to a
high temperature and a high humidity condition, even after the
reflow soldering.
[0008] Further, it is likely that Zn is eluted from a solder into a
flux, possibly incurring problems such as a lowered insulation
resistance and a generation of migration, since Zn is employed in
solder.
[0009] A melting point of the Sn--In--Ag--Bi based solder alloy is
close to that of an Sn--Pb solder, similarly to the case for the
Sn--Zn based solder. When bonding this alloy system with the Cu
base material, a Cu--Zn compound is not formed since Zn is not
employed. Accordingly, such a phenomenon does not occur that a
bonding strength in a bonding surface with Cu is significantly
lowered under the high temperature and high humidity
atmosphere.
[0010] Meanwhile, in case of soldering to an Ag electrode, an
Ag--In compound is formed in a bonding surface. It has been
confirmed that the compound's phase grows large as time passes and
becomes fragile, whereby an interface strength becomes lowered. In
addition, it is observed that if a heat cycle is applied in a state
where the parts are bonded, a solder of a joint is deformed. A
technological development for PCB has been directed to a substrate
designing of a narrower pitch, and a more high level packaging
technology has been required.
[0011] Such a technical trend draws a concern that deformation of
the solder may cause short circuits. Further, since the solder
contains a large amount of rare and expensive Indium (In), the
material cost amounts high and the continuous future supply may not
be secured.
[0012] Solder alloys having melting points in the range from
180.degree. C. to 210.degree. C. are widely used in a soldering
method in which soldering is performed several times (flow
soldering after reflow soldering, reflow soldering after reflow
soldering, or the like), due to temperature characteristics
thereof. Here, the problematic point is that a place soldered once
is peeled off in subsequent soldering processes. Particularly, in a
large-scale IC parts or the like, parts leads float from a PCB,
together with solder. The reason for such a phenomenon is that on
the second soldering or thereafter, a joint solder formed by a
former soldering is partially melted and a bonding strength thereof
decreases, and, in such a state, the joint is peeled off by a
bending of a PCB or deformations of the parts. Namely, in a solder
alloy's property, the bigger a difference between a temperature
where a solder alloy begins to melt (hereinafter, referred to as a
solidus line) and a temperature where the solder alloy completely
melts (hereinafter, referred to as a liquidus line), the higher the
possibility that the joint is peeled off.
[0013] In a conventional art, e.g., Japanese Patent No.2599890
(reference 1), a mechanical strength or a creep resistance is
improved by the addition of Zn to an Sn--Ag based solder.
[0014] At the same time, it is disclosed that a melting point
becomes lower by the addition of Zn or In.
[0015] However, the Ag concentration described in reference 1 is
too high by as much as 1% in weight or more. For example, in an
alloy of a high Ag concentration (1 weight %) such as
Sn-6Zn-6In-1Ag, endothermic peak area, whose summit is in the
vicinity of a melting point of 200.degree. C., becomes large, as
can be seen from the measurement results of DSC (differential
scanning calorimetry) in FIG. 9. As a result, under a reflow
soldering condition same as that of the Sn--Pb solder, it is likely
that the solder is not sufficiently melted down. If the solder is
not sufficiently melted down, fluidity of the solder is
deteriorated, whereby a joint is not fully formed. In that case,
voids in the solder remain to thereby lower the bonding strength.
Further, in Japanese Patent Laid-Open Publication Heisei No.
9-174278 (reference 2), In is added to an alloy of a near Sn--Zn
eutectic composition so as to lower a melting temperature and
improve wettability to parts metallization. Further, Ag is added so
as to make Zn phase needle like solidification microstructures in
the Sn--Zn--In alloy into spheroidal solidification microstructures
and to finely disperse them. Therefore, the Zn concentration is set
at from 6 to 11% in weight, and the Ag concentration is set at from
0.5 to 3% in weight.
[0016] The conventional Pb-free solder may incur various problems
such as poor wettability due to Zn, which is a problem in the
Sn--Zn(--Bi,--Al) based solder, and a lowered bonding strength with
Cu electrode under the condition of the high temperature and high
humidity. Further, using rare metals such as In and Ag becomes a
problem in the Sn--In--Ag--Bi based solder alloy.
SUMMARY OF THE INVENTION
[0017] It is, therefore, an object of the present invention to meet
such a condition that a melting temperature characteristic is same
as that of an Sn--Pb based solder and to solve the problems of the
conventional Sn--Zn(--Bi,--Al) based solder and the Sn--in--Ag--Bi
based solder.
[0018] Particularly, it is an important object to improve solder
joint reliability under the condition of the high temperature and
high humidity.
[0019] For achieving the objects, a solder alloy in accordance with
the present invention is based on an Sn--Zn--In--Ag system having,
in weight, 0.3%<Zn<5.0%, 0.1%<In<4.0%,
0.1%<Ag<0.4%, and the balance Sn.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The above and other objects and features of the present
invention will become apparent from the following description of
preferred embodiments given in conjunction with the accompanying
drawings, in which:
[0021] FIG. 1 is a graph for showing peel strengths of solder
joints of solders in accordance with Example 1 of the present
invention, as a function of exposure time;
[0022] FIGS. 2A to 2E show DSC measurement results of solder alloys
as a function of temperature, in case when Zn is added to
Sn-3In-0.3Ag of Example 1 of the present invention while varying
the Zn concentration in the range from 2 to 6 weight %;
[0023] FIGS. 3A to 3C describe typical views of structures, in case
when a small amount of Ag is added to Sn-4Zn-3In of Example 2 of
the present invention;
[0024] FIG. 4 illustrates a graph for showing electrochemical
corrosion potentials as a function of time, in case when a small
amount of Ag is added to Sn-4Zn-3In of Example 3 of the present
invention;
[0025] FIGS. 5A to 5E explain variations of melting temperatures as
a function of Ag concentration, when a small amount of Ag is added
to Sn-4Zn-3In of Example 1 of the present invention;
[0026] FIG. 6 offers a graph for showing variations of mechanical
properties of solder alloys as a function of In concentration, in
case when In is added to Sn-4Zn-0.3Ag of Example 6 of the present
invention in a range from 0 to 10 weight %;
[0027] FIG. 7 sets forth to a graph for showing variations of
mechanical properties of solder alloys in accordance with Example 8
of the present invention, as a function of exposure time;
[0028] FIG. 8 presents a graph for showing variations of mechanical
properties of another solder alloys in Example 8 of the present
invention, as a function of exposure time; and
[0029] FIG. 9 depicts a DSC measurement result of a conventional
Sn-6Zn-6In-1Ag alloy.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Hereinafter, preferred embodiments of the present invention
will be described in detail with reference to accompanying
drawings.
[0031] In accordance with the present invention, a solder alloy is
an Sn--Zn--In--Ag solder containing a small amount of Ag for
preventing a bonding interface strength from being lowered when a
joint of a Cu base material with a solder is exposed to the high
temperature and high humidity atmosphere, based on an Sn--Zn--In
based solder having a melting point of 210.degree. C. or less.
[0032] In aspects of the melting temperature and bonding
reliability, it is preferable that the concentration of each
element in such a solder alloy is as follows, in weight:
[0033] 3.0%<Zn<5.0%;
[0034] 0.1%.ltoreq.In<20.0%; and
[0035] 0.1%.ltoreq.Ag.ltoreq.0.4%.
[0036] Hereinafter, the composition range will be explained.
[0037] The Zn concentration is from about 3.0% to 5.0% in weight.
When the Zn concentration is less than 3.0% in weight, a melting
point of the solder cannot be lowered to about 200.degree. C.
Further, if the Zn concentration is less than 3.0% in weight, a
difference between a solidus temperature and a liquidus temperature
becomes large even though the In concentration is increased. As a
result, in multiple soldering processes, it is likely that the
parts joints are peeled off.
[0038] On the other hand, when the Zn contention is more than 5.0%
in weight, a bonding interface strength with a Cu film is lowered
under the condition of the high temperature and high humidity.
Further, if the Zn concentration increases, wettability of the
solder becomes deteriorated, resulting in oxidation of the solder
and a lowered electrical insulation of the joint.
[0039] The In concentration is from 0.1 to about 20.0% in weight.
When the concentration is less than about 0.1% in weight, a melting
point cannot be expected to be lowered. If the In concentration is
more than 20.0% in weight, a solidus temperature in the solder
melting point becomes too low. In case of the Sn-20In, a solidus
temperature is 153.degree. C. If the solidus temperature decreases,
the solder is melted and peeled off when being exposed to a high
temperature environment.
[0040] Further, the same failure may possibly be caused due to heat
generation by using equipment. Still further, since the solidus
temperature (153.degree. C.) and the liquidus temperature
(199.degree. C.) of the Sn-20In are separated from each other too
far, such a phenomenon may occur that the solder is peeled off in
the second soldering process or thereafter.
[0041] The Ag concentration is between 0.1% and 0.4% in weight. If
the concentration is less than about 0.1% in weight, an effect that
prevents a bonding strength from being lowered cannot be obtained
when exposing to an environment of high temperature and high
humidity after soldering.
[0042] If the Ag concentration exceeds 0.4% in weight, the solder
tends to melt at a higher temperature in a melting point
temperature area of the solder, so that fluidity of a molten solder
becomes poor in the reflow soldering process.
[0043] Further, it is more preferable that the composition range is
as follows below, in weight:
[0044] 0.3%<Zn<5.0%;
[0045] 0.1%.ltoreq.In.ltoreq.4.0%; and
[0046] 0.1%.ltoreq.Ag.ltoreq.0.4%.
[0047] If the In concentration in the solder alloy increases,
ductility of the solder alloy becomes deteriorated. Further, if the
In concentration is 4% in weight and less, elongation of 30% or
greater can be assured. Therefore, a stress can be relieved since
the solder is deformed when a stress due to heat-shock or the like
is on. In contrast, if the solder does not have ductility, crack
may possibly be developed in the solder joint in case where a PCB
or parts are expanded or shrunk.
[0048] Meanwhile, `high temperature and high humidity` of the
present invention means a circumstance of 85.degree. C. and 85% RH
(relative humidity).
EXAMPLES
Example 1
[0049] In Example 1, a peel strength of a joint having, in weight,
3% In and 0-6% Zn (the remaining portion was Sn) was measured, with
respect to a variation of a bonding strength when exposed to an
environment of the high temperature and high humidity.
[0050] First, a solder alloy, which was mixed to have a
predetermined composition, of about 1 kg was held at 230.degree. C.
And then, QFP (Quad Flat Package) parts of 0.65 mm in pitch and 100
pins are fixed to a Cu-attached glass epoxy PCB by using an
adhesive. This specimen was applied to a flux, and then, subjected
to soldering by dipping into the solder. A soldered article was
washed with acetone by using a microwave washing machine, so that
residuals of the flux were removed. A soldered PCB specimen after
being washed was put into a hygro-thermostat (constant temperature
and humidity oven) kept at 85.degree. C. and 85% RH, and then, a
peeling strength of a lead bonding strength was measured for every
250 hours.
[0051] FIG. 1 shows a variation of a lead bonding strength, in case
when soldering QFP parts with a solder having, in weight, 3% In,
0-6% Zn, and the balance Sn. Here, 0-6% Zn means that the Zn
concentration is in the range from 0 to 6% in weight. Further, it
can be noted that as the Zn concentration increases, a bonding
strength when being exposed to a condition of high temperature and
high humidity significantly declines. Further, in case where the Zn
concentration is 6% in weight, a bonding strength at exposure time
of 500 hours becomes 1 kgf or less.
[0052] Namely, as the Zn concentration in the solder increases,
bonding strengths of the parts tend to decrease under an
environment of the high temperature and high humidity. Zn phases in
the solder diffuse into a bonding surface and react with a Cu base
material under the high temperature and high humidity atmosphere,
to thereby form and grow a Cu--Zn compound layer. In the course of
the process, Zn oxidizes due to an effect of high humidity, whereby
a bonding strength in an interface of the Cu--Zn compound layer of
the bonding surface with the solder is significantly lowered. As
can be seen from FIG. 1, it is preferable that the Zn concentration
is less than about 5% in weight.
[0053] Meanwhile, FIGS. 2A to 2E describe DSC measurement results
of solders, each having, in weight, 3% In, 2-6% Zn, 0.3% Ag, and
the balance Sn. If the Zn concentration is less than 3% in weight,
a melting point of a metal exceeds 210.degree. C. Therefore, it is
preferable that the Zn concentration is greater than about 3% in
weight.
[0054] Further, if the Zn concentration is greater than 5% in
weight, a bonding strength under the high temperature and high
humidity is gradually lowered. Thus, it is preferable that the Zn
concentration is less than about 5% in weight.
Example 2
[0055] Example 2 was carried out for observing a structure, in case
when a small amount of Ag is added to an Sn-4Zn-3In. Each solder
having, in weight, 4% Zn, 3% In, 0.1-0.5% Ag, and the balance Sn of
about 0.6 g was melted on a ceramic plate to form a sphere shape,
and in that state, cooled in the air. A section of each solder
particle was polished and observed by using scanning electron
microscope (SEM). The results were described in FIGS. 3A to 3C.
[0056] As is known from FIGS. 3A to 3C, needle like Zn phases
decrease as the Ag concentration increases. Further, it can be
noted that spheroidal Zn--Ag phases increase in FIGS. 3B and 3C.
Still further, a fine structure of the solder is confirmed. Zn
phases are finely dispersed, so that a connection between the Zn
phases disappears. Accordingly, oxidation of Zn, which causes to
lower a bonding strength, does not spread towards an inside of the
solder, and lowering of a bonding strength under the condition of
the high temperature and high humidity is suppressed.
[0057] In case where the Ag concentration is 0.1% in weight, many
needle like Zn phases are observed, as shown in FIG. 3A. However, a
spheroidal Zn--Ag layer is certainly confirmed.
Example 3
[0058] In Example 3, a variation of an electrochemical corrosion
potential would be explained, in case when a small amount of Ag is
added to the Sn-4Zn-3In.
[0059] Each solder having, in weight, 4% Zn, 3% In, 0-0.5% Ag, and
the balance Sn was prepared with a bar shape having a cross section
of 5 mm.times.5 mm. A surface of the bar-shaped specimen was
polished with water resistance polishing paper of 1200 mesh, and
then, subjected to buffing by using Al.sub.2O.sub.3 suspension.
Subsequently, the specimen was immersed into a 3.5 wt. % NaCl water
solution at 25.degree. C. Further, by using a standard electrode
employing a silver electrode, a silver chloride electrode, and a
saturated KCl water solution, an electromotive force difference,
which is generated between Ag of the standard electrode and the
solder specimen, was measured. The result was shown in FIG. 4.
Still further, as a reference sample, an electrochemical corrosion
potential of the Sn-3In solder not containing Zn was described.
[0060] As is known from FIG. 4, oxidation of Zn in the solder
becomes difficult as an electromotive force is close to that of the
Sn-3In solder. Namely, by the addition of Ag with 0.1% in weight or
more, such an effect can be obtained that oxidation is prevented
from progressing.
Example 4
[0061] In Example 4, an observation result of a bonding surface
would be explained when soldering the Sn-4Zn-3In--0.3Ag with a Cu
plate. The Sn-4Zn-3In-0.3Ag solder of 0.3 g was placed on the Cu
plate and applied to a flux. Then, it was heated on a 230.degree.
C. heat plate and soldered. After this specimen was filled into a
resin, polished, and evaporated, a section of the bonding surface
was observed by using SEM and X-ray micro analyzer (XMA). As a
result of the observation using SEM and XMA, a Zn layer and an Ag
layer could be observed to be generated in a bonding surface
between the solder and the Cu plate. Namely, it can be known that a
Zn--Ag phase is formed in the bonding surface between the Cu plate
and the bonding surface. If a Zn--Cu compound phase is formed in a
bonding surface, oxidation in an interface of the solder with the
Zn--Cu compound progresses, so that a bonding strength is lowered.
Namely, by preventing the formation of the Zn--Cu compound layer, a
bonding strength can be prevented from being lowered.
Example 5
[0062] In Example 5, a variation of a melting point would be
explained, in case when a small amount of Ag is added to the
Sn-4Zn-3In. FIGS. 5A to 5E show measurement results of melting
points of solders, each having, in weight, 4% Zn, 3% In, 0-0.5% Ag,
and the balance Sn, by using DSC. As can be seen from FIGS. 5A to
5E, it could be noted that as the Ag concentration increases, a
peak representing a heat absorbing amount in the vicinity of
205.degree. C. to 210.degree. C. becomes large, and a melting
amount of the solder increases in this temperature area. If the Ag
concentration becomes 0.5% in weight, an endothermic peak in the
vicinity of 205.degree. C. to 210.degree. C. grows as much as
substantially same as that in the vicinity of 190.degree. C. As a
result, in case when being employed as a solder, it is difficult to
be melted. In other words, the solder is melted at a lower
temperature (about 193.degree. C.) first, and melted again at a
higher temperature. Further, wettability or fluidity of the solder
becomes deteriorated.
[0063] From the aforementioned measurement results, by an addition
of Ag with 0.1% in weight or more, an electrochemical corrosion
potential is improved. On the other hand, if Ag is added more than
0.5% in weight, as described by DSC measurement of the alloy,
higher temperature peaks increase. Accordingly, the solder is
difficult to be melted, so that wettability or fluidity
characteristic thereof becomes deteriorated.
[0064] Further, if Ag is added to the solder containing Zn, needle
like Zn phases decrease and spheroidal Zn--Ag phases increase. As a
result, a fine structure of the solder can be confirmed by a
structure observation. While needle like Zn phases are observed in
case where the Ag concentration is 0.1% in weight, an effect of
improving an electrochemical corrosion potential can be obtained
even in that case, as mentioned above.
[0065] Further, by the addition of Ag, the Zn--Ag compound phase is
formed in a bonding surface when soldering on a Cu, to thereby
serve as a barrier layer for suppressing a reaction between Cu and
Zn. As a result, formation of the Zn--Cu compound layer, which
tends to be easily oxidized, can be suspended, so that oxidation in
the bonding surface is suppressed to thereby prevent the bonding
strength from being lowered.
Example 6
[0066] Each solder having, in weight, 4% Zn, 0-10% In, 0.3% Ag, and
the balance Sn was molded to a plate shape at a temperature higher
than a solder liquidus temperature by 50.degree. C., and a tensile
specimen was prepared.
[0067] The specimen was JIS4 specimen. The tensile test was
performed at a tensile rate of 5.0 mm/min.
[0068] The result was described in FIG. 6. As is evident from FIG.
6, elongation of 30% or greater is held in the range from 0 to 4%
In, in weight.
Example 7
[0069] Preferably, a Pb-free solder material formed of a solder
alloy and a flux is utilized in a wire solder and a cream solder.
Here, the solder alloy is based on the Sn--Zn--In--Ag system
having, in weight:
[0070] 3.0%<Zn<5.0%;
[0071] 0.1%.ltoreq.In.ltoreq.4.0%;
[0072] 0.1%.ltoreq.Ag.ltoreq.0.4%; and
[0073] the balance Sn.
[0074] Further, as the flux, a known flux may be used.
Example 8
[0075] In Example 8, a solder bonding strength would be explained
by using a solder alloy, which has at least one element selected
from a group consisting of Ni, Ti, Mg, Al, and Co, based on the
Sn--Zn--In--Ag system having, in weight:
[0076] 3.0%<Zn<5.0%;
[0077] 0.1%.ltoreq.In.ltoreq.4.0%; and
[0078] 0.1%.ltoreq.Ag.ltoreq.0.4%.
[0079] Here, a total concentration of at least one element is in
the range from 0.001% to 0.05% in weight and the remainder is
Sn.
[0080] The high temperature and high humidity test was carried out
on the following samples. FIG. 7 exhibits variations of bonding
strengths thereof. Bonding strength was measured by the same method
as in Example 1. The samples were prepared by using solder alloys,
each having one of the aforementioned elements and performing a
reflow soldering on a Cu film.
[0081] In FIG. 7, F represents a standard Pb-free solder alloy of
the present invention. Further, A, B, C, D, and E have the same
composition with F other than Sn, and contain 0.004% Ti, 0.01% Ni,
0.01% Mg, 0.05% Al, and 0.05% Co, in weight, respectively. And, the
remaining portion thereof is Sn. Comparing bonding strengths after
being exposed for 1000 hours under the condition of the high
temperature and high humidity, the samples A, B, C, and E are found
to be superior to the standard F. Further, it can be noted that the
sample D maintains a bonding strength at least equal to or greater
than F.
[0082] FIG. 8 shows variations of bonding strengths under the high
temperature and high humidity on three solder joint compositions:
Sn-8Znn-3Bi, Sn-4Zn-3In-0.3Ag, and Sn-4Zn-3In--0.3Ag-0.003Ti.
Further, the solder joints are formed by the same manner as in
Example 1. As can be seen from FIG. 8, the addition of Ti is
clearly demonstrated to be effective after 1500 hours.
[0083] Further, in the comparative Sn-8Zn-3Bi, a bonding strength
becomes less than 1 kgf after 250 hours. Other elements such as Ni,
Mg, Al, and Co provide the same effects as Ti.
Example 9
[0084] A Pb-free solder material formed of a solder alloy and a
flux of Example 9 is utilized in a wire solder and a cream solder.
Here, the solder alloy has at least one element selected from the
group consisting of Ni, Ti, Mg, Al and Co, based on the
Sn--Zn--In--Ag having, in weight:
[0085] 3.0%<Zn<5.0%;
[0086] 0.1%.ltoreq.In.ltoreq.4.0%; and
[0087] 0.1%.ltoreq.Ag.ltoreq.0.4%.
[0088] Here, a total concentration of at least one element is in
the range from about 0.001% to about 0.05% in weight and the
remainder is Sn.
[0089] Further, as the flux, a known flux may be used.
[0090] As mentioned above, in accordance with the present
invention, the Zn concentration is in the range from about 3 to 5%
in weight, so that solder joint reliability can be improved under
the high temperature and high humidity atmosphere. Further, a
solder alloy of the present invention may be a bar solder (molten
solder), and a Pb-free solder alloy suitable for a diffusion
bonding. Still further, the present invention may include a solder
joint of electrical and electronic equipment using the solder alloy
of the present invention.
[0091] A Pb-free solder using a solder alloy in accordance with the
present invention has a melting temperature substantially equal to
that of a conventional Sn--Pb solder. Therefore, the current Sn--Pb
soldering method and the current parts or production equipment can
be employed as it is. Further, a Pb-free solder material having a
solder characteristic with excellent bonding strengths of the parts
can be provided.
[0092] Further, since a difference between a solidus temperature
and a liquidus temperature is small, floating of the parts leads
can be suppressed, even in case where packaging processes are
performed many times over. Still further, when the joint is exposed
to the high temperature and high humidity atmosphere, the bonding
strength can be prevented from being lowered.
[0093] While the invention has been shown and described with
respect to the preferred embodiments, it will be understood by
those skilled in the art that various changes and modifications may
be made without departing from the spirit and scope of the
invention as defined in the following claims.
* * * * *