JP3446517B2 - Pb-free solder material and electronic equipment using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to Pb having low toxicity.
The present invention relates to a free solder alloy and a mounted product using the same. This solder alloy can be applied to the connection of electronic parts such as LSI to a circuit board such as an organic board,
It is an alternative to the Pb-Sn eutectic solder used for soldering at 230 ° C.

[0002]

2. Description of the Related Art Conventionally, in order to manufacture an electronic circuit board by connecting an electronic component such as an LSI to a circuit board such as an organic board, an S
An n-Pb eutectic solder, an Sn-Pb solder having a similar melting point in the vicinity of the Sn-Pb eutectic solder, or a solder alloy in which a small amount of Bi or Ag is added to these is used.

These solders contain about 40% by weight of Pb.
include. All solder alloys have a melting point of about 18
The temperature was 3 ° C, and soldering at 220 to 230 ° C was possible. Moreover, the reliability at a high temperature of about 150 ° C. could be guaranteed.

[0004]

However, the above-mentioned Sn-
Pb contained in the Pb eutectic solder is a heavy metal that is toxic to the human body, and disposal of products containing this Pb causes pollution of the global environment and adverse effects on living organisms.
The pollution of the global environment is caused by elution of Pb due to rain or the like from electric appliances containing Pb that have been left in the field. The elution of Pb tends to be accelerated by recent acid rain. Therefore, in order to reduce environmental pollution, a low-toxicity solder alloy containing no Pb is required as a substitute material for the above-mentioned Sn-Pb eutectic solder that is used in large quantities.

The Pb-free solder alloy as a substitute material for the Sn-Pb eutectic solder must have the following characteristics.

First, it must be possible to perform soldering at a temperature of 220 to 230 ° C. like the conventional Sn-Pb eutectic solder. This is because soldering at higher temperatures is difficult due to the heat resistance of electronic components such as LSI and circuit boards such as organic boards. For this reason, the liquidus temperature of the solder alloy must be approximately 210 ° C. or lower.

The wettability of this solder alloy is Sn-
Pb eutectic solder, or Sn- which has been used in the past
It should be almost the same as the Ag eutectic solder (3.5% by weight of Ag and the remaining Sn solder). If this Pb-free solder has extremely poor wettability due to surface oxidation or the like as compared with the conventional solder, improvement of the soldering atmosphere, development of a flux suitable for the solder material, a cleaning material, and a cleaning method, This causes major problems such as development of materials for the electrode parts to be soldered.

As the solder structure, it is important that there is no needle-shaped or other large crystal having a high aspect ratio, which may trigger crack propagation. When these needle-shaped crystals grow from the solder surface, an electrical short circuit may occur.

Also, as high a temperature as possible, that is, 150 ° C.,
It must be possible to ensure reliability at least at 125 ° C. This is because when the electric product is used, the temperature of the solder connection portion may rise due to the heat generated by the component itself or the use environment being high temperature.

Further, the elongation of the solder alloy is important for applying the thermal expansion mismatch between the electronic component and the circuit board. Therefore, a Pb-free solder alloy having the above characteristics is required.

However, such a Pb-free solder alloy has not been provided so far. The binary alloy Sn-Ag eutectic solder or Sn-Bi eutectic solder is Pb-free solder and is used as a solder for layer connection, but the melting points are 221 ° C. and 138 ° C., respectively. Requires a soldering temperature of about 240 ° C., and it is difficult for the latter to secure reliability at high temperatures. Also, S
The n-Zn solder has a melting point of Sn-Zn eutectic solder of 19
Since the temperature is 9 ° C., it is effective as a substitute material for the Sn—Pb eutectic solder in terms of melting point, but it was difficult to secure sufficient wettability in the atmosphere due to oxidation of Zn.

Further, Pb as described in JP-A-7-1179 or JP-A-7-88680.
There are free solder alloys, but the former has a melting point of about 138 ° C, and the latter is difficult to solder at 220 to 230 ° C, and neither of them could be a substitute material for Sn-Pb eutectic solder. .

Therefore, an object of the present invention is to provide a Pb-free solder which satisfies the above-mentioned conditions and a mounted product using the same.

[0014]

The above object is 10% by weight.
25 wt% Bi, 1.5 wt% to 3 wt% Ag,
Sn-Ag- composed of the remaining Sn and unavoidable impurities
Bi-based solder or Sn-Ag-Bi-Cu-based solder alloy containing less than 1% by weight of Cu in this solder alloy, more preferably Sn-Ag containing less than 0.1% by weight of Cu.
It can be achieved by using a Bi-Cu based solder alloy. The ternary eutectic amount of the solder alloy in these ranges which melts at a low temperature is 20% or less.

The reason why the solder alloy of the present invention is selected will be described below.

The melting characteristics of the Sn-Ag-Bi solder in which Bi is 0 to 60% by weight, Ag is 0 to 5% by weight, and the remaining Sn is in the range, were examined in detail. As an example of this study, 2 wt% Ag, 13 wt% Bi, the remaining Sn solder (a), 2 wt% Ag, 15 wt% Bi, the remaining Sn solder (b), 2 wt% Ag, 22 wt% B
The melting characteristics of the solder (c) of i and the remaining Sn are shown in FIG. In these, the solder alloys of each composition are weighed in equal amounts, melted and solidified using a reflow furnace, and the melting characteristics are examined by differential thermal analysis. The reason for melting and solidifying using a reflow furnace is to make the cooling rate of the sample the same as that during normal soldering. The differential thermal analysis was performed at a heating rate of 2 ° C./min. As a result of conducting such a detailed study on the composition within the above range, 220 to 230
It has been found that the liquidus temperature must be at least 210 ° C. or lower and the Bi amount must be at least 10 wt% or more in order to perform the soldering at ℃.

In FIG. 2, 10% by weight of Bi, 2% by weight of A
g, remaining Sn solder (d), 10 wt% Bi, 3 wt% Ag, remaining Sn solder (e), and 10 wt%
Bi, 4 wt% Ag, and the remaining Sn solder (f) 3
The microstructures of the various solder alloys are shown. This is after melting this solder alloy at 240 ℃ for 30 seconds, then 80 ℃ /
The structure was cooled in minutes, the structure was cross-section polished, and observed with a metallurgical microscope. From now on, Sn in (d) and (e)
In the -Ag-Bi solder, spherical Bi crystals and small crystals of Ag3Sn were found between Sn round crystals.
It was found that large needle crystals of Ag3Sn were crystallized in the -Ag-Bi solder (f). This result shows that when the amount of Ag was changed similarly for other Bi amounts and the structure was observed, similarly, when the Sn-Ag binary eutectic line was crossed in the direction of increasing the concentration of Ag, the primary crystals of Ag3Sn were formed. It had been deposited. Therefore, it was found that the Ag amount must be 3% by weight or less so as not to exceed this line. Further, Ag is added to improve the mechanical properties of the solder, but the effect was not observed at 1.5% by weight or less. It was also found that the liquidus temperature rises as the amount of Ag decreases, and the difference between the liquidus temperature and the solidus temperature increases. Therefore, the Ag amount must be 1.5% by weight or more.

Next, conditions for ensuring reliability at 150 ° C. and at least 125 ° C. will be shown. The solidus temperature of the solder is important to ensure the reliability at such a high temperature. From the detailed study of the melting characteristics of the solder as shown in FIG. 1, it was found that in this Sn-Ag-Bi system, when Bi is about 10 wt% or more, a part that melts at around 138 ° C occurs. This is affected by the cooling rate at the time of making the measurement sample, and if the cooling rate is high, Bi
Of about 18% by weight or less, this melting peak does not appear, but it was found that in a sample cooled by a cooling rate during normal soldering, Bi was melted even in the range of 10% by weight to 18% by weight. It was The part that melts at 138 ° C. is the part of the ternary eutectic composition of Sn—Ag—Bi. Therefore, on the Sn-Ag binary eutectic line, the ratio of the portion that melts at 138 ° C when the Bi amount is changed is set to the same amount of 3
It was determined by comparison with the peak calorific value of the solder of the original eutectic composition (1 wt% Ag, 57 wt% Bi, balance Sn), and is shown in FIG. From this, it was found that the rate of melting at 138 ° C. changes smoothly depending on the amount of Bi. Three
It can be said that there is no problem in practical use as long as the ratio of the original eutectic is small. Therefore, as a result of conducting various temperature cycle tests and examining, it was found that the proportion of the ternary eutectic should be about 20% or less, and Bi should be 25% by weight or less. The Bi amount for ensuring the reliability at this high temperature could be confirmed also by the tensile test at high temperature. FIG. 4 shows the tensile strength at 150 ° C. when the Bi content was changed. This is because the strength at 150 ° C is a measure of reliability at high temperatures. Tensile test is 0.1m
The tensile speed was m / min. The reason for setting the tensile speed to 0.1 mm / min is that the maximum strain rate that the sample undergoes during the actual temperature cycle test is reproduced, so that the tensile rate is equivalently converted. From this, it was also found that when Bi is 25% by weight or less, it has tensile strength at 150 ° C. and can withstand use at high temperature. The reason why the strength is guaranteed at 150 ° C. even if the ternary eutectic exists to some extent is based on the formation mechanism of the ternary eutectic. That is, when the amount of Bi is increased, a ternary eutectic crystal is generated, but it has strength because it is scattered in the gaps of the Sn crystal having a high melting point. If Bi further increases, S
The amount of Bi in the n-crystal increases, the melting point of the Sn crystal itself decreases, and the amount of ternary eutectic in the gap of the Sn crystal also increases, so that the strength cannot be obtained. Here, Bi is 25% by weight and the ternary eutectic is 20%.
Up to the range of%, the ternary eutectic does not completely fill the gaps of the Sn crystal, so that it has strength at 150 ° C. Similarly, the tensile strength was measured by conducting a tensile test at 125 ° C. and shown in FIG. 5. When Bi is 25 wt% or more, the tensile strength is 5 MPa or less, but Bi is 25 wt% or less. Then, it was found that the tensile strength increases as Bi decreases, and the reliability at high temperature can be secured.

Cu was added to improve the structure.
Cu is usually Cu-Sn in Sn-Ag-Bi solder.
Exists as a compound of Since the Cu-Sn compound has a small spherical shape when the amount of Cu is small, it is dispersed between Sn to form a dispersion-strengthened alloy. This is effective only if a small amount of Sn-Cu compound is present. Since Cu dissolves in Sn to about 0.006 wt%, it is necessary to add 0.006 wt% or more of Cu to form a Cu-Sn compound. However, when the Cu content is 0.1% by weight or more, the solder begins to become brittle. This is because the Cu—Sn compound becomes large in size and is hard to be deformed because it is hard, and the flexibility of the entire solder joint is poor. This is because the connection using solder balls, which is a structure without leads, or the soldering joint becomes smaller due to the higher mounting density, the heat generation of the electronic circuit increases, and the strain applied to the connection portion increases. This is especially important for connections that require solder flexibility, such as Further, when the Cu content is 1% by weight or more, deterioration in another item is observed. First, regarding the wettability, FIG. 6 shows the wet spread of the solder when Cu was added to the solder of 15 wt% Bi, 2.5 wt% Ag, and the remaining Sn. It was found that the wet spread becomes maximum in the case of, and the wet spread decreases with the Cu concentration at a Cu concentration higher than that, and the wettability deteriorates at 2 wt% as compared with the case where Cu is not added. . Further, when the amount of Cu is large, Sn in the solder is consumed for forming a compound with Cu, so that the amount of Ag is relatively increased, and large acicular crystals of Ag3Sn are likely to occur. The structure of the solder in which 0.5 wt%, 1 wt%, and 2 wt% Cu were added to the solder containing 15 wt% Bi, 2.8 wt% Ag, and the remaining Sn was observed. As the Cu-Sn compound increases as the amount increases, 1% by weight or more of C
It was found that large crystals of Ag3Sn were generated when u was added. This large crystal of Ag3Sn can trigger crack propagation. Therefore, it is conceivable to reduce the amount of Ag in advance in order to prevent this, but on the contrary, the liquidus temperature rises. From the above, Cu
Was 1 wt% or less, preferably 0.1 wt% or less.
Wettability of solder alloys in the above composition range is
It is almost at the same level as n-Ag eutectic solder, and conventional flux and electrode material can be used as they are.

FIG. 7 shows the elongation at room temperature when the Bi content was changed on the binary eutectic line. The elongation of the solder alloy within the above composition range is 17% or more at room temperature. . There is no problem in practical use.

Further, solderability at 220 to 230 ° C.,
In order to improve the reliability at high temperature, 13% by weight to 20% by weight of the composition selected as described above is used.
i, 2 wt% to 3 wt% Ag, the remaining Sn, and Sn-Ag-Bi solder composed of unavoidable impurities, or Sn- containing less than 1 wt% Cu in this solder alloy.
Ag-Bi-Cu based solder alloy, and Sn-Ag-Bi in which Cu is contained in the ternary based solder alloy in an amount of less than 0.1% by weight.
-Cu based solder alloy is desirable. This is because when Bi is 13% by weight or more, the liquidus temperature is lower than when Bi is 10% by weight.
This is because soldering at 230 ° C. can be facilitated.
Further, Ag also has a function of lowering the liquidus temperature in a region where the amount of Ag is smaller than that of the Sn-Ag binary eutectic line, and when the amount of Ag is 2% by weight or more, reflowability is further improved and mechanical properties are also improved. This is because it is further improved. Also, the Bi amount is 20
If it is less than 10% by weight, the proportion of the ternary eutectic melted at around 138 ° C is 10% or less, the tensile strength at 150 ° C is about 5 MPa or more, and the tensile strength at 125 ° C is 15M.
Since it has about Pa or more, reliability at high temperature such as strength, creep characteristics, vibration, and impact is improved, and a margin of reliability can be expanded for electric products used at high temperature.

As shown above, the effective range of the Sn-Ag-Bi solder alloy was selected.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The results of investigating the properties of solders having 6 compositions shown in Table 1 are described below.

[0024]

[Table 1]

(Embodiment 1) As an example of the present invention, 1
Alloys of 5 wt% Bi, 2 wt% Ag and the balance Sn were made. This alloy has a liquidus temperature of 207 ° C. and a solidus temperature of 156 ° C., but there is a part where the ternary eutectic melts near 138 ° C., and the ratio is 5%, which is not a practical problem. The tensile strength at room temperature is 77MPa, the tensile strength at 150 ° C is 11MPa, the tensile strength at 125 ° C is 22MP.
a, the elongation at room temperature was 19%. In addition, the wettability in air is 91% of that of Sn-Ag eutectic, and Sn-A
It can be said that it is about the same as g-eutectic solder. This solder alloy was pulverized and kneaded with a flux component to prepare a solder paste. Using this solder paste, QFP (Quad Flat Package) -LSI with 0.5 mm pitch and 208 pins
Was soldered to a glass epoxy substrate, and a temperature cycle test of −55 ° C. 30 minutes to 125 ° C. 30 minutes (1 hour / 1 cycle) was performed. The leads of the QFP-LSI are Sn-plated. The maximum temperature during soldering is 220 ° C.
Met. On the surface of the fillet of the corner pin where the most stress is exerted, a follow-up investigation was carried out by an electron microscope from the initial stage up to 1000 cycles, but a slight change in the surface did not occur, and cracks leading to disconnection did not occur. Compared with the -Pb eutectic solder, there was no difference. The cross section of this corner pin was polished and observed, but it was confirmed that no crack was generated. Therefore, the solder alloy having the above composition can be used as a substitute material for the Sn-Pb eutectic solder. For this solder alloy, BGA (Ball Grid Array), CSP (Chip Size P
It can also be used as a solder ball for connections such as ackage). Further, since the surface oxidation is small, it can be used as a solder material for flow soldering. Further, it can be used as a solder foil, and can be applied to die bonding of chips, module mounting, and sealing.

(Embodiment 2) Similarly, as an example of the present invention, 15 wt% Bi, 2.5 wt% Ag, and the balance S
n alloy was made. The liquidus temperature of this alloy is 204
C., and the solidus temperature was around 155.degree. C. and 138.degree. C., the melting ratio of the ternary eutectic was 5%. Tensile strength at room temperature is 78
The tensile strength at MPa and 150 ° C. was 10 MPa, and the elongation at room temperature was 20%. The wettability in the atmosphere is
It was 92% of the Sn-Ag eutectic. This solder alloy was made into a solder paste and the same temperature cycle test as in Example 1 was performed. As a result, the solder fillet surface at the corner where most stress acts is up to 1000 cycles,
Similar to the result of Example 1, only a slight change occurred on the surface, and no crack leading to disconnection occurred. Therefore, the solder alloy of Example 2 is effective as a substitute material for the Sn-Pb eutectic solder.

(Third Embodiment) Similarly, as an example of the present invention, 20% by weight of Bi, 2.5% by weight of Ag, and the remaining S
n alloy was made. The liquidus temperature of this alloy is 200
C., the solidus temperature was around 138.degree. C. and 138.degree. C., and the melting ratio of the ternary eutectic was 10%. Tensile strength at room temperature is 7
The tensile strength at 5 MPa and 150 ° C. was 5 MPa, and the elongation at room temperature was 25%. The wettability in the atmosphere is
It was 87% of the Sn-Ag eutectic. This solder alloy was made into a solder paste and the same temperature cycle test as in Example 1 was performed. As a result, the solder fillet surface at the corner where most stress acts is up to 1000 cycles,
Similar to the results of Example 1, only a slight change was caused on the surface, cracks leading to disconnection did not occur, and were comparable to the Sn-Pb eutectic solder. Therefore, Example 3
The above solder alloy is effective as a substitute material for the Sn—Pb eutectic solder.

(Embodiment 4) Similarly, as an example of the present invention, 15 wt% Bi, 2.8 wt% Ag, 0.5
An alloy of Cu at the weight percent and the balance Sn was prepared. The liquidus temperature of this alloy was 204 ° C., the solidus temperature was 157 ° C., and the melting ratio of the ternary eutectic was 5%. The tensile strength at room temperature was 83 MPa, the tensile strength at 150 ° C. was 11 MPa, and the elongation at room temperature was 21%. The wettability in the air was 90% of that of the Sn-Ag eutectic. This solder alloy is made into a solder paste, and TSOP (Thin Small Outline)
Package) and chip parts were soldered to a glass epoxy substrate, and a temperature cycle test was performed under the same conditions as in Example 1. QSOP-LS with long leads has to be applied to the difference in thermal expansion in the solder because the TSOP and chip parts have short leads or are parts without leads.
It is a severer connection than I. As a result of observing the solder fillet surface at the corner portion of the TSOP subjected to such a temperature cycle test up to 1000 cycles, some deterioration was observed, but it was confirmed that cracks leading to disconnection did not occur. It was In addition, there was no significant change in the chip component, and it was confirmed by observation of the cross section that no crack was generated, which was comparable to that of the Sn-Pb eutectic. A shear test was conducted on the chip components soldered in this way.
After the high temperature storage test in the above, and the above temperature cycle test 1
Even after 000 cycles, deterioration in shear strength was not seen compared to the initial stage. In addition, the Sn-P that has been used conventionally
It had about the same shear strength as the b eutectic. Also, there was no problem in the electrical continuity test.

(Embodiment 5) An example in which an alloy of 18% by weight of Bi, 2% by weight of Ag, and the remaining Sn is used for connection of BGA is shown. As shown in FIG. 8, the solder balls 2 having the above composition were soldered onto the BGA body 1. Solder ball diameter is 0.
It was 76 mm and the soldering temperature was 225 ° C. The BGA 3 was printed with the solder paste 5 having the same composition on the printed board 4 side and soldered under the same conditions. Through the above process, it is possible to make a low-toxicity BGA connection without using Pb. The same temperature cycle test as in Example 1 was conducted on the BGA connected to this printed board, and it was found that there was no problem in practice.

Even if the solder ball 2 connected to the BGA body is a high melting point solder, for example, Sn—Ag eutectic solder, if the solder of the present invention is used as the solder used for the printed circuit board side, 220 Connection at ~ 230 ° C is possible. In this way, the solder of the present invention can be used for connection using solder balls such as BGA.

(Embodiment 6) 15% by weight of Bi, 2.
A method of manufacturing an electronic circuit board for an 8 mm video using an alloy of 5 wt% Ag, 0.08 wt% Cu and the balance Sn will be described. First, this solder alloy was pulverized to a size of 25 to 45 μm, and this was kneaded with a flux component to prepare a solder paste. 0.15m of this solder paste
It was individually supplied onto a printed wiring board using a metal mask having a thickness of m. Various electronic components were mounted on a printed circuit board supplied with this solder paste by using a component mounting machine, and soldering was performed through a nitrogen reflow furnace. The oxygen concentration in the nitrogen reflow furnace was 100 ppm. The soldering temperature varies depending on the heat capacities of various components even on the same substrate, but the preheating is approximately 150 ° C, and the maximum temperature is set to 230 ° C even at the highest temperature. After this,
Similarly, the back side was printed with solder paste, mounted with various parts, and heated by nitrogen reflow. This electronic circuit board has a QFP-LSI of 0.4 mm pitch, 10
A chip component having a size of 1.0 mm in length and 0.5 mm in width called 05 is included. No cleaning was performed after soldering. After soldering in this manner, the visual inspection of the soldered portion was performed using an automatic visual inspection device.
As a result, the false alarm rate was low because the solder surface had less gloss as compared with the conventional Sn-Pb eutectic. The solderability was also compared to that of a conventional soldered substrate using Sn-Pb eutectic, but the wetting spread to the Cu pad on the printed circuit board was slightly poor, but it was at a practically sufficient level.

Among them, due to the positional deviation when mounting the parts,
There were several chip parts that were missing, which could be easily corrected with a soldering iron.

The 8 mm video electronic circuit board manufactured in this manner was incorporated into an actual 8 mm video main body, and product inspections such as an electrical check, a vibration test, and a high temperature and high humidity test were conducted, but there was no particular problem. As described above, by using a Sn-Ag-Bi-Cu solder having low toxicity that does not contain Pb, by heating the soldering temperature up to 230 ° C., an electronic circuit board that is less toxic to the environment and organisms can be manufactured. I was able to.

(Embodiment 7) 15% by weight of Bi, 2.
An alloy containing 8% by weight of Ag and the remaining Sn was soldered to a 0.5 mm pitch QFP-LSI and TSOP. The maximum soldering temperature was 230 ° C. The lead electrodes of these electronic parts have conventionally been solder-plated with a composition of 90% by weight Sn and 42% by weight Pb in 42 alloy (hereinafter,
Sn-10Pb) is used. However, since these also contain toxic Pb, the lead electrode also needs to be Pb-free. Therefore, in the present embodiment, after the Cu plating is applied on the 42 alloy,
Solder plating with a composition of Bi of wt% and the balance of Sn (hereinafter,
Sn-8Bi). The Cu plating had a thickness of 5 μm, and the Sn-8Bi plating had a thickness of 10 μm. The same temperature cycle test as in Embodiment 1 was performed on the above-mentioned soldered substrate, but sufficient reliability was obtained.

The reason why the lead electrode is configured as described above is that the substrate is warped during the split board work after soldering or the probing test, or a large stress is applied to the solder connection portion of the LSI or the like connected by handling or the like. This is because it is necessary to secure the strength of the solder connection portion that can withstand it. Therefore, the connection strength between the solder alloy of the present invention and the leads using various Pb-free materials was examined in order to obtain a structure having sufficient connection strength, which will be described below.

A model lead having various solder plating, Pd plating, etc. on its surface was prepared. The material of the model lead is 42 alloy, and Cu is used as the base of the surface plating.
Three types of plating, Ni plating, and no base were examined. The model lead has a width of 3 mm and is bent at an angle of 90 ° so that the length of the soldered portion is about 22 mm. In these soldering methods, a Cu foil having a width of 3.5 mm and a length of 25 mm on a printed circuit board is overlaid with a solder foil having the same composition as that of the present invention and having the above-mentioned model leads. Then, it was soldered at a maximum temperature of 220 ° C. in the atmosphere. At this time, the chlorine content is 0.2
% Flux was used. After washing this, pull it vertically at a speed of 5 mm / min to perform a peel test,
The strength of the fillet portion where the strength was the highest was determined. In the peel test, the initial strength after soldering and the deterioration of connection strength due to the change with time after soldering are taken into consideration.
After leaving it for 168 hours at ℃, and considering the case that the wettability of the lead electrode deteriorates, the model lead is kept at 150 ℃ for 16 hours.
After leaving for 8 hours and soldering, three types were performed. Within the scope of the invention, the solder composition is Bi content, Ag content,
The amount of Cu was changed and examined. As a result, the same tendency was observed in this solder composition range, and C was used as a base on the 42 alloy.
It was found that the connection strength was improved when u plating was applied. This is because the reactivity of Bi with 42 alloy is low, so that a sufficient compound cannot be produced and strength cannot be obtained as compared with the conventional Sn-Pb eutectic. Since the connection strength increases due to the presence of Cu, sufficient connection strength can be obtained by using a Cu-based lead frame instead of the 42 alloy lead. It was also found that when the composition of the surface is a Sn-Bi composition containing up to about 25% by weight of Bi, sufficient connection strength can be obtained. Of these results,
15 wt% Bi, 2.8 wt% Ag, the remaining Sn solder, and Sn-8Bi plating of 10 μm on 42 alloy.
Fig. 9 shows the strength of the fillet portion of a model lead in which Cu undercoat was plated on the No. 42 alloy to 5 µm and then Sn-8Bi was plated to 10 µm. FIG. 9 also shows the fillet portion strength in the case of the combination containing Pb which is conventionally used. From this, in the structure in which the Cu underlayer plating is applied on the 42 alloy and the Sn-8Bi plating is applied on the 42 alloy, the connection strength is larger than that in the case where the Sn-8Bi plating is directly applied on the 42 alloy, and the conventional Sn-Pb eutectic solder used and Sn-10Pb
It was found that a connection strength higher than the configuration with the plating lead can be obtained. As described above, in the solder alloy of the present invention, Cu is used as an underlayer, or a Cu-based lead frame is used, and a surface treatment such as Sn-8Bi plating is performed on the solder alloy to form a connection portion having sufficient strength. can get.

[0037]

As described above, the solder alloy of the present invention can provide a low-toxicity Pb-free solder as a substitute material for the Sn-Pb eutectic solder which has been used in large quantities in the past. This solder alloy has the same soldering temperature as before and has the same wettability as Sn.
-Since it is about the same as Ag eutectic solder, no special development of flux or electrode material is required. Further, since the ternary eutectic amount that melts at a low temperature is 20% or less, the reliability at a high temperature can be secured and the electronic component can be connected to the circuit board with high reliability.

[Brief description of drawings]

FIG. 1 shows melting characteristics of three types of Sn-Ag-Bi solders.

FIG. 2 is a photograph showing the structures of three types of Sn—Ag—Bi solder.

FIG. 3 is a ratio of the ternary eutectic when the Bi amount near the Sn-Ag binary eutectic line is changed.

FIG. 4 shows the tensile strength at 150 ° C. when the Bi content was changed.

FIG. 5: Tensile strength at 125 ° C. when changing the amount of Bi.

FIG. 6 shows wetting characteristics when changing the amount of Cu in Sn—Ag—Bi solder.

FIG. 7 shows elongation characteristics at room temperature when the Bi content is changed.

FIG. 8 shows an example in which the present invention is applied to BGA.

FIG. 9 is a connection strength between the solder of the present invention and a lead.

[Explanation of symbols]

1. BGA body 2. Solder balls 3. BGA 4. Printed board 5. Solder paste

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H05K 3/34 512 H01L 21/92 603B (72) Inventor Toshiharu Ishida 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock company Hitachi Ltd. Production Technology Laboratory (72) Inventor Masahide Harada 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Stock Company Hitachi Production Engineering Laboratory (72) Inventor Megumi Hamano 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Stock Company Hitachi, Ltd. Production Technology Laboratory (72) Inventor Kenichi Yamamoto 5-20-1, Kamimizumoto-cho, Kodaira-shi, Tokyo Hitachi, Ltd. Semiconductor Business Division (56) Reference JP-A-9-216089 (JP, A) JP-A-9-327791 (JP, A) JP-A-9-192877 (JP, A) JP-A-10-52791 (JP, A) JP-A-8-132277 (JP, A) ) Patent flat 8-206874 (JP, A) JP flat 9-326554 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) B23K 35/26 H05K 3/24 H05K 3 / 34 H01L 21/60

Claims (12)

(57) [Claims] 1. An electronic device comprising a circuit board on which a predetermined wiring pattern is formed and an electronic component provided with an electrode connected to the wiring pattern, wherein the electrode of the electronic component is plated with Cu and Sn-Bi. An electronic component having a plated electrode and a wiring pattern of the circuit board are made of Sn- which is composed of 10 wt% to 25 wt% Bi, 1.5 wt% to 3 wt% Ag, and the rest Sn.
An electronic device characterized by being connected by Ag-Bi solder. 2. An electronic device comprising a circuit board on which a predetermined wiring pattern is formed and an electronic component provided with an electrode connected to the wiring pattern, wherein the electrode of the electronic component is plated with Cu and Sn-Bi. An electronic component having a plated electrode and a wiring pattern of the circuit board are provided with 10 wt% to 25 wt% Bi, 1.5 wt% to 3 wt% Ag, less than 1 wt% Cu, and the rest. S
An electronic device characterized by being connected by a Sn-Ag-Bi-Cu solder composed of n. 3. An electronic device in which a semiconductor device having a lead electrode and an electrode of an electronic substrate are connected by solder, the lead electrode being a 42 alloy lead, a Cu layer plated on the 42 alloy lead, and Sn. -Having a Bi layer, the solder comprising from 10 wt% to 25 wt% Bi,
1.5 wt% to 3 wt% Ag and the balance S being Sn
An electronic device characterized by being an n-Ag-Bi lead-free solder. 4. An electronic device in which a semiconductor device having a lead electrode and an electrode of an electronic substrate are connected by solder, the lead electrode having 42 alloy leads, a Cu layer plated on the 42 alloy leads, and Sn. A Bi layer, the solder comprising 10 wt% to 25 wt% Bi, 1.
An electronic device characterized by being a Sn-Ag-Bi-Cu based lead-free solder in which 5 wt% to 3 wt% Ag, 1 wt% Cu, and the balance Sn. 5. An electronic device in which a semiconductor device having a lead electrode and an electrode of an electronic substrate are connected by solder, the lead electrode having a Cu lead and a Sn—Bi layer plated on the Cu lead. The solder contains Bi of 10 wt% to 25 wt% and 1.5 wt% of Bi.
Wt% to 3% by weight Ag and the balance Sn-A
An electronic device which is a g-Bi lead-free solder. 6. An electronic device in which a semiconductor device having a lead electrode and an electrode of an electronic substrate are connected by solder, the lead electrode having a Cu lead and an Sn—Bi layer plated on the Cu lead. The solder is composed of 10 wt% to 25 wt% Bi, 1.5 wt% to 3 wt% Ag, less than 1 wt% Cu, and the balance S.
Sn-Ag-Bi-Cu based lead-free solder which is n. 7. The electronic device according to claim 3, wherein the solder connection portion that connects the lead electrode of the semiconductor device and the electrode of the electronic substrate has a Sn—Ag—Bi layer. Original eutectic amount is 2
An electronic device characterized by being 0% or less. 8. The electronic device according to claim 1, wherein a Bi content of the Sn—Bi layer is 25% by weight or less. 9. A method of manufacturing an electronic device for solder-connecting a lead electrode of a semiconductor device and an electrode of an electronic substrate, comprising: 42 alloy lead, and a Cu layer and a Sn—Bi layer plated on the 42 alloy lead. A lead electrode having 10 wt% to 25 wt% Bi and 1.5 wt% to
Sn-Ag-Bi with 3 wt% Ag and the balance Sn
A method for manufacturing an electronic device, comprising a step of soldering and connecting using a lead-free solder. 10. A method for manufacturing an electronic device, in which a lead electrode of a semiconductor device and an electrode of an electronic substrate are solder-connected, comprising 42 alloy leads, and a Cu layer and a Sn—Bi layer plated on the 42 alloy leads. A lead electrode having 10 wt.% To 25 wt.% Bi, 1.5 wt.% To 3 wt.
% Of Ag, 1% of Cu less than 1%, Sn-Ag-Bi-Cu based lead-free solder with the rest being Sn. . 11. A method of manufacturing an electronic device, in which a lead electrode of a semiconductor device and an electrode of an electronic substrate are connected by soldering, wherein a Cu lead and Sn plated on the Cu lead are formed.
Using a Sn-Ag-Bi lead-free solder in which the lead electrode having a -Bi layer is 10 wt% to 25 wt% Bi, 1.5 wt% to 3 wt% Ag, and the balance is Sn. A method of manufacturing an electronic device, comprising a step of soldering and connecting. 12. The method of manufacturing an electronic device according to claim 9, wherein the soldering temperature is 220 ° C. to 230 ° C. Method.