JPH07336043A - Solder, solder connecting method and mounting structure for electronic component - Google Patents

Abstract

PURPOSE:To prevent the generation of a bridge by using solders having smaller surface tension than that of Sn-Pb eutectic solder and different solid- and liquid- phase temperatures. CONSTITUTION:Since eutectic solder has no difference between solid- and liquid- phase temperatures, the solder arriving at a melting point abruptly forms an unstable state due to the operations of a wet spreading strength, surface tension tending to be integrated with liquid and the gravity. Solder paste tends to, when becoming a high temperature, form a bridge by the operation of the tension. In order to improve it, solder having small surface tension and a difference between solid- and liquid-phase temperatures is used. An experiment for measuring the melting separability of the solder is conducted by using a solder copper 1, a copper pad 2 and a glass epoxy board 3. This experiment decides the separability by the state of the bridge formed after a solder line 1 is placed on the pad 2 and then allowing it to reflow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder material and a mounted product using the same.

[0002]

2. Description of the Related Art Currently, Sn-Pb alloy, especially Sn63-Pb37 eutectic solder (for example, cream solder, JP No. 60-257988) is mainly used. A solder paste is used to supply the solder used for connection.

By the way, QFP (Q
Parts such as uad Flat Package) are becoming narrower pitch and more pins. When a solder paste is supplied to the pads of the substrate to be connected to this LSI having a narrow pitch and a large number of pins, a bridge is generated between terminals when reflowing due to dripping of the solder paste.

In the case of eutectic solder, when the solder reaches the melting point, it melts instantly. Therefore, when the solder paste on a certain pad is in contact with the solder paste on the adjacent pad, the solder is melted by the surface tension before the wet spread on the pad. A bridge will be formed between the pad and. Such behavior during melting is peculiar to eutectic solder. When connecting an LSI having a narrow pitch and a large number of pins using eutectic solder, it is difficult to prevent the occurrence of bridges. Therefore, there is a limit in narrowing the pitch due to the solder.

[0005]

In the prior art, it was difficult to eliminate the occurrence of bridges when soldering an LSI having a narrow pitch and multiple pins using eutectic solder.

Use of a low melting point solder (melting point 165 ° C.) containing 8 wt% of Bi in Sn-Pb type solder is excellent in melt separation property, etc. (Taniguchi, Material of Micro-Joint Research Committee, MJ-S-55 -9
1, 1991). However, such a low melting point solder has a melting point of Sn-Pb eutectic (melting point 183
However, it is difficult to secure reliability at high temperatures as high as that of eutectic solder.

An object of the present invention is to prevent the occurrence of bridges by soldering with a solder having a composition having a property that bridges are unlikely to occur.

An object of the present invention is to provide a solder in which bridging is unlikely to occur.

[0009]

It has been found that the achievement of the above object can be solved by using a solder having a small surface tension and a difference in solid phase temperature and liquid phase temperature.

Since conventional eutectic solder has no difference between the solid phase temperature and the liquidus temperature, the solder having reached the melting point has a wetting and spreading force that tends to wet and spread on the pads on the substrate and the leads of the LSI. And the surface tension that the liquid tries to unite, and the gravity,
Suddenly creates an unstable state due to the action of. Also, the solder paste is liable to drip at high temperatures, and the LSI
When the leads are mounted, the paste squeezes out, so that the solder paste may come into contact with the adjacent pads. In such a case, the bridge is easily formed by the action of the surface tension.

To form this bridge, the wetting and spreading force of the melted solder reaching the melting point to the pads and leads of the molten solder and the surface tension of the solder itself trying to gather together start to work at the same time. Has the most influence.

In order to improve this, it has been found effective to utilize the property in the semi-molten state when the temperature is between the solid phase temperature and the liquid phase temperature.

The solder in a semi-molten state is a state in which a solid phase and a liquid phase are mixed, and the viscosity is extremely high. Further, since the surface tension acts on the liquid phase portion but not on the solid phase portion, the surface tension cannot act on the entire solder surface. Therefore, the surface tension is apparently considerably low. On the other hand, the solder in the semi-molten state can wet and spread the solder in the liquid phase portion to the pad on the substrate or the lead of the LSI by the action of the spreading force. For this reason, in the semi-molten solder, the wetting and spreading force is superior, and the action of surface tension tending to collect in one place is weak. Therefore, unlike the eutectic solder, both do not start working at the same time, and it is possible to prevent the occurrence of bridges.

Further, even when a bridge is generated due to an excessive amount of solder, if the surface tension of the solder is low,
Since the solder can further spread on the pads on the substrate and the leads of the LSI, the bridge can be separated.

As a concrete composition of the solder having such characteristics, in the present invention, the following points A ', B, B', C ', D in the phase diagram of the Sn-Bi-Pb ternary alloy are used.
We propose a solder characterized by being based on an alloy having a composition within the range surrounded by.

A '(Sn: 52 wt%, Pb: 48 wt
%, Bi: 0 wt%) B (Sn: 48 wt%, Pb: 49 wt%, Bi: 3
wt%) B '(Sn: 48 wt%, Pb: 48 wt%, Bi: 4
wt%) C '(Sn: 54 wt%, Pb: 42 wt%, Bi: 4
wt%) D (Sn: 58 wt%, Pb: 42 wt%, Bi: 0
wt%) In addition, a solder characterized by being based on an alloy having a composition within the range surrounded by the following points A, B, C, and D in the phase diagram of the Sn-Bi-Pb ternary alloy is proposed. .

A (Sn: 53 wt%, Pb: 47 wt)
%, Bi: 0 wt%) B (Sn: 48 wt%, Pb: 49 wt%, Bi: 3 w
t%) C (Sn: 54 wt%, Pb: 42.5 wt%, Bi:
3.5 wt%) D (Sn: 58 wt%, Pb: 42 wt%, Bi: 0 w
t%) A solder having a composition within the above range is added to the above alloy.
By including Sb in an amount corresponding to ˜0.5 wt%, the surface tension can be further reduced and the effect described above can be further enhanced. Further, if the solder having the composition within the above-mentioned range contains Ag in an amount corresponding to 0 to 3 wt% of the above alloy, it is possible to prevent silver cracking.

Incidentally, as a solder particularly suitable for connection at a narrow pitch, there has been no example so far focused on an alloy having a composition in which the liquidus temperature and the solidus temperature are different as in the present invention.
The inventor of the present application is the first to discover and clarify the use of the alloy having such characteristics.

[0019]

[Function] Sn with a temperature difference between the solid phase temperature and the liquid phase temperature
-Pb-based solder is soldered at about the same soldering temperature (about 220 to 230 ° C) as that of the conventional eutectic solder. From the viewpoint of high temperature reliability, it is more preferable that the solder has a melting point (about 170 ° C.) that is almost the same as that of a conventional eutectic solder.

In this case, the wetting and spreading force of the liquid phase to the LSI lead and the pad acts from the solid-liquid coexisting state to the liquid phase state. On the other hand, the surface tension acts on the liquid phase part but not on the solid phase part, and apparently the surface tension of the entire solder surface drops extremely (most of the liquid phase part's surface tension binds to the solid phase part). Spent on energy), and loses the ability to spread wet. Therefore, bridging can be prevented. Further, by the similar operation, the already bridged state can be separated uniformly. This allows
The number of man-hours for correction can be reduced, and the cost for manufacturing mounted products can be reduced. At the same time, it is possible to provide the same level of reliability as the conventional Sn63-Pb37 eutectic solder.

[0021]

EXAMPLE FIG. 1 is a schematic view of an experiment for measuring the melt separation property of solder. The experiment is performed using a solder wire (1), a copper pad (2) and a glass epoxy substrate (3). This experiment shows the solder wire on the adjacent copper pad (2).
Melt separability is judged by the state of the bridge formed after the reflow with the (1). The reason for using the solder wire is to eliminate the factor of variation as much as possible and to be able to see only the effect of the composition of the solder. Although the bridge generation rate changes depending on the copper pad size, the solder wire diameter (solder amount), and the pitch, it is necessary to select conditions that match the two in order to evaluate the melt separation property. Here, the spacing between the centers of the copper pads (2) is 0.5 mm pitch, so the solder wire diameter φ0.3 mm was selected as the optimum condition. About copper pad width, 0.28mm, 0.30mm, 032mm 3
Experiments were conducted with different types. The resulting bridges are sized.

FIG. 2 is a schematic diagram showing the bridge size. As shown in FIG. 2 (a), the bridge (5) extending over two copper pads (2) has a size 2 bridge, and the bridge (6) shown in FIG. 2 (b) has 3 copper pads. pad
(2) A bridge spanning between the two is called a size 3 bridge.

FIG. 3 (a) shows the relationship between the bridge size and the number of bridges when an experiment was conducted with Sn63-Pb37 eutectic solder (solid phase temperature: 183 ° C., liquidus temperature: 183 ° C.).
(b) The size of the bridge when the experiment was performed with Sn54-Bi1-Pb45 solder (solid phase temperature: 182 ° C, liquidus temperature: 196 ° C), which has a melting point and soldering temperature similar to Sn63-Pb37 eutectic solder And the number of bridges is shown. 3 (a) and 3 (b), the vertical axis represents the number of bridges and the horizontal axis represents the size of generated bridges.

In the case of Sn63-Pb37 eutectic solder, the number of bridges of any size is less than 10, but is small.
You can see that a big bridge like size 5 is made. The reason why such a result is obtained is that a large amount of solder flows into one place, and the other portions do not have a sufficient amount of solder to form a bridge, so that a bridge is not formed.

In the case of Sn54-Bi1-Pb45, although many small bridges such as size 2 are made up of 30 or more,
There is no large bridge of size 4 or more.

The difference in the results depending on the composition of the solder is considered to be due to the following mechanism.
In other words, in the case of Sn63-Pb37 eutectic solder, it will be in a molten state instantaneously, and at the same time (or sooner) it will try to spread on the copper pad by the action of the wetting and spreading force, and at the same time by the action of surface tension. , A flow occurs in which the solder moves laterally (solder wire direction) and tries to gather in one place. The result is a large bridge. On the other hand, the solder having the composition of Sn54-Bi1-Pb45 has a temperature range in which it is in a semi-molten state. In this temperature range, the solder has a high viscosity because it is in a solid-liquid coexisting state. Also, the surface tension itself is lower than that of Sn63-Pb37 eutectic solder, and the force to gather in one place even after completely melting is small. Therefore, the lateral flow of the solder is small and a large bridge cannot be formed. Therefore, many small bridges are formed. Since the wetting and spreading force can act regardless of the level of the surface tension, the solder can wet and spread on the copper pad.

Further, it was confirmed that the difference in the results depending on whether the LSI is mounted or not is due to the following mechanism.

When an LSI is mounted and the lead is placed on a copper pad, the solder is sucked to form a fillet on the heel of the lead as the solder melts. It will be drawn (being attracted). Therefore, it was found that the solder in the bridge portion, which had already been formed by the time the reflow was started, moved so as to be separated into the pads, and the small bridges having the bridge sizes of 2 and 3 disappeared. On the other hand, when the bridge is large (for example, when the bridge size is 4 or 5), the solder in the bridge portion cannot be completely attracted (cannot be attracted) only by forming the fillet. Therefore, the solder remains in the bridge portion, and the bridge remains unresolved.

From the above, the solder having a composition capable of forming a large-sized bridge in this experiment is a solder which easily causes a bridge even in actual use, while the solder having a composition capable of producing a large number of small bridges is actually used. At times, it turned out that the solder did not form a bridge.

Based on such knowledge, it was decided to evaluate the melt separability of the solder by paying attention to the average value of the sizes of the bridges (average bridge size). Since a solder having a composition in which many small bridges are formed is a solder in which bridging is difficult to occur, it can be seen that the smaller the average bridge size, the better the melt separation property.

FIG. 4A is a graph showing the relationship between the composition of the Sn--Pb based solder and the average bridge size. The vertical axis represents the average bridge size, and the horizontal axis represents the Sn concentration. From FIG. 4 (a), it can be seen that even in the Sn—Pb based solder, the melt separation property is improved by making the solid phase temperature and the liquid phase temperature different.
However, it was observed that the melt separation property of Sn50-Pb50 deteriorated. This is because the liquid phase temperature of Sn50-Pb50 was higher than the reflow temperature, which caused a decrease in wettability.

FIG. 4 (b) shows the relationship between the Bi concentration and the average bridge size for Sn-Bi-Pb45 type solders having good separability. The vertical axis represents the average bridge size, and the horizontal axis represents the Bi concentration. From FIG. 4 (b), it can be seen that in the Sn-Bi-Pb45 system, the melt separability is constant regardless of the Bi concentration. The Sn-Bi-Pb45 system has a difference between the solid phase temperature and the liquid phase temperature, but the melting point tends to decrease as the Bi concentration increases. From this, it is understood that the melt separability does not depend on the melting point.

FIG. 5 is a graph showing the relationship between the difference between the solid phase temperature and the liquid phase temperature and the average bridge size. Figure 5
The ordinate represents the average bridge size, and the abscissa represents the difference between the solid phase temperature and the liquid phase temperature. The shaded area in the figure is the area in which the solder, which was evaluated to have excellent melt separation properties in this experiment, is distributed.

It can be seen from FIG. 5 that the average bridge size decreases as the difference between the solid phase temperature and the liquid phase temperature increases. That is, it is understood that the solder having the excellent melt-separability has the solid phase temperature and the liquid phase temperature different (having a difference).

From the above, an experiment is conducted in which a solder fine wire having an appropriate size is placed on a terminal to be soldered so as to cross it and reflowed, and the average bridge size of the bridge obtained as a result of the experiment is evaluated. Then, it was found that the difficulty of occurrence of the bridge of the solder can be determined.

The solder determined to be excellent in melt separability by this method remains excellent in melt separability even if the pitch dimension is changed. Further, such a solder is effective not only for the batch reflow, but also for any connection method (for example, a method of pressing the lead with a heating electrode). Furthermore, QFP (Quad Flat Package) and TCP (Tape Carri
er Package), BGA (Ball Grid Array), PGA (Pin G)
It is still effective for mounting all kinds of electronic components such as packages such as rid array) and SOP (Small Outline Package), and flip chips. Further, it can be used for precoating on a pad using a solder paste.

FIG. 6 is a state diagram of the Sn-Pb-Bi ternary solder. Points A, B, C, D, A ', B', C'in the figure
The compositions of E, F, G, H, I, I ′ and I ″ are as follows.

A (Sn: 53 wt%, Pb: 47 wt)
%, Bi: 0 wt%) B (Sn: 48 wt%, Pb: 49 wt%, Bi: 3 w
t%) C (Sn: 54 wt%, Pb: 42.5 wt%, Bi:
3.5 wt%) D (Sn: 58 wt%, Pb: 42 wt%, Bi: 0 w
t%) A '(Sn: 52 wt%, Pb: 48 wt%, Bi: 0
wt%) B '(Sn: 48 wt%, Pb: 48 wt%, Bi: 4
wt%) C '(Sn: 54 wt%, Pb: 42 wt%, Bi: 4
wt%) E (Sn: 63 wt%, Pb: 37 wt%, Bi: 0w
t%) F (Sn: 60 wt%, Pb: 40 wt%, Bi: 0w
t%) G (Sn: 55 wt%, Pb: 45 wt%, Bi: 0w
t%) H (Sn: 50 wt%, Pb: 40 wt%, Bi: 0 w
t%) I (Sn: 46 wt%, Pb: 46 wt%, Bi: 8 w
t%) I '(Sn: 48 wt%, Pb: 46 wt%, Bi: 6
wt%) I '' (Sn: 50 wt%, Pb: 46 wt%, Bi:
In the figure, the solid line (7) is a eutectic line, the dotted line (8) is a liquid phase temperature of 175 ° C., and the dotted line (9) is a liquid phase temperature of 200.
The line of ° C is shown.

For the purpose of suppressing the occurrence of bridges, in the present invention, in the range surrounded by A ', B, B', C ', D, more preferably in the range surrounded by ABCD (in the figure,
It is proposed to use solder with a composition within the shaded area). The reason why the composition in such a range is preferable is as follows.

AB (or A'B) has a liquidus temperature of 20.
The level is 0 ° C., which is the limit for ensuring sufficient wettability by reflowing at 220 ° C.

CB (or C'B ') is a Bi concentration 4 wt% line, and as the Bi concentration increases, the separability increases,
The last separation is slow, and a tail-like breakage occurs. Depending on the process, the time required for the separation is long and easy to be oxidized, and the apparent viscosity is increased and the breakage tends to occur. However, it was found that it was not observed when Bi was 4 wt% or less. For example, on the Pb: 46 wt% line, three types of solder having different Bi concentrations (here, I ″ (Bi: 4 wt%), I ′ (Bi: 6 wt%), and I (Bi: 8
wt%) and the Bi concentration is 6 wt%
With the above solder, a phenomenon of tailing was observed. Therefore,
The Bi content was 4 wt% or less.

Next, the CD (or C'D) will be described. The position of the point D is in a state where Bi is not contained and the average bridge size is 2.4 or less (Fig. 4 (a)
(See) was decided from the viewpoint of.

When the eutectic line (7) of the ternary system is approached, the temperature difference between the liquid phase and the solid phase becomes small and the separability deteriorates. Therefore, the limit is point C (average bridge size
2.32) was selected.

The discussion so far has been based on experimental results on solder wires. Next, an example of an evaluation result based on an experiment using an actually used solder paste will be described.

In the experiment, a solder mask was prepared using a metal mask.
This was done by printing a strike on the substrate and reflowing it. Then, the evaluation was performed based on the ratio of the paste short circuit portion remaining as a bridge after reflow (referred to as a bridge ratio here). The experiment and evaluation are
Both the case where QFP was mounted at the time of reflow and the case where it was not mounted were performed.

FIG. 7A shows the metal mask (1
0) is shown. The mask thickness of the metal mask (10) is 0.15 mm. Holes (11) are formed in the metal mask (10) at intervals corresponding to the pads for printing the solder paste. The opening width of the hole (11) is 0.25 mm. Also, when printing the solder paste, the solder paste on the pads next to each other
In order to experimentally create a state in which the strikes are connected, the predetermined hole (11) and the hole (11) are connected in the vicinity of the center. Hereinafter, the hole (11) and the opening portion connecting the holes are collectively referred to as "bridge pattern (11)". The experiment includes
Two types of metal masks (10) having a width of the bridge pattern (11) of 0.15 mm and 0.20 mm were used.

FIG. 7 (b) shows the substrate (3) used in this experiment. Copper pads (2) are formed on the substrate (3). substrate
(3) is for 0.5 mm pitch QFP. Copper pad
The width of (2) used four kinds of 0.25 mm, 0.28 mm, 0.30 mm, 0.32 mm.

In the experiment, a solder which easily forms a bridge and a solder which hardly forms a bridge were used. Sn63-Pb37 eutectic solder was used as the solder that easily forms a bridge. On the other hand, as a solder that does not easily become a bridge,
A Sn37-Bi18-Pb45 low melting point solder and a solder having a composition within the range surrounded by ABCD in FIG. 6 (Sn53-Bi2-Pb45) were used. The values of the surface tension of these solders are listed for reference. The surface tension of Sn63-Pb37 eutectic solder at 500 ° C. is 460 × 10 ⁻³ N / m. Sn37-B
The surface tension of i18-Pb45 low melting point solder at 500 ℃ is
430 × 10 ⁻³ N / m. It is known that the Sn-Pb-based solder generally has a smaller surface tension as the Sn ratio decreases. Further, the surface tension of Bi is smaller than that of Sn and Pb, and when Bi is added, the surface tension of the Sn-Pb solder decreases.

Solder paste using metal mask (10)
FIG. 8A shows a state in which (12) is printed on the substrate (3). substrate
On the (3) and the copper pad (2), a solder paste (12) is printed in a pattern corresponding to the bridge pattern (11). A paste short circuit portion (13) is formed so as to connect the copper pad (2) and the copper pad (2). In the actual process, the paste short circuit part (13), which is considered to be the cause of the bridging, is the paste paste (12) when the paste (12) is printed, components are mounted, and reflow is performed during preheating. This is what happens when the copper pads (2) contact each other.

Printed solder paste on the QFP (1
Fig. 8 (b) shows the mounting of 4).

The evaluation results of the experimental results are shown in FIGS. 9 and 10.

FIG. 9 shows the state of FIG. 8 (a) reflowed.
It is a graph which shows the relationship between a copper pad width and a bridge rate in the case of doing. The vertical axis represents the bridge ratio (%) and the horizontal axis represents the copper pad width (m
m). In the graph, □ is Sn63-Pb37 eutectic solder, ▽ is S
n37-Bi18-Pb45 low melting point solder, ○ indicates the result of Sn53-Bi2-Pb45. When reflow is performed without mounting QFP (14), the spread of solder on the lead (15) and the lead (15)
Since there is no fillet formation in the heel part, the solder amount becomes excessive. In the case of Sn63-Pb37 eutectic solder, the paste short circuit part (13) remained as a bridge. On the other hand, Sn53-Bi2-Pb45 has about half the paste short-circuit part (13) separated, and in the case of Sn37-Bi18-Pb45 low melting point solder, it is about 90%.
The paste short-circuit part (13) was separated.

FIG. 10 is a graph showing the relationship between the copper pad width and the bridge ratio when the state shown in FIG. 8B is reflowed. The vertical axis is the bridge ratio (%), the horizontal axis is the copper pad width
(mm). In the graph, □ is Sn63-Pb37 eutectic solder, ▽ is Sn37-Bi18-Pb45 low melting point solder, and ○ is Sn53-Bi2-P.
The result of b45 is shown. When reflowing with the QFP (14) installed, the spread of solder on the lead (15) and the reflow
Since fillets are formed in the heel portion of the cord (15), the solder is absorbed by them and the bridge ratio takes a smaller value than that in FIG. In the case of Sn37-Bi18-Pb45 low melting point solder,
All the paste short circuits (13) were separated. Also, Sn53-Bi2
-Pb45 also separated more than 95%. On the other hand, S
In the case of n63-Pb37 eutectic solder, about half of the paste short circuit part (13) remained without separation.

From these results, it can be said that the Sn63-Pb37 eutectic solder is a solder that is more likely to cause a bridge than Sn37-Bi18-Pb45 low melting point solder or Sn53-Bi2-Pb45.

On the other hand, Sn53-Bi2-Pb45 having a composition in the range surrounded by ABCD in FIG. 6 has a low melting point of Sn37-Bi18-Pb45 when it is reflowed by mounting QFP (14). It had a melting and separating property similar to that of solder. Also, this solder is Bi
Since the concentration is 2%, there is almost no decrease in strength due to the addition of Bi. In other words, this solder (Sn53-Bi2-Pb45)
It had the same level of reliability as n63-Pb37 eutectic solder. further,
The results of this melt-separation evaluation experiment using solder paste are consistent with the results of experiments using solder wires. Therefore, when soldering is performed by using the solder having the excellent melt separation property, it is possible to prevent the occurrence of the bridge. Furthermore, even if a large number of "bridge" -shaped bridges are formed in advance by soldering between a large number of pads, these solders can be evenly separated from each other with reflow.

As an application of the present invention, a multi-pin high density LSI
An example of TCP used as a package of the above will be shown. TCP is usually soldered by heating while pressure-bonding a lead to a substrate pre-coated with solder. For this precoat, it is possible to use a solder having an excellent melt separation property. It is possible to supply the solder onto the copper pad by printing the solder having an excellent melt separation property on the copper pad and performing reflow. Narrow pitch T
In the case of a board for CP, the precoat by the solder paste is apt to cause a bridge between adjacent pads when the paste has a droop.

When precoating is performed with the solder of the present invention having an excellent melt separation property, it becomes possible to prevent the occurrence of bridges. Further, the cost can be kept lower than that of other precoat methods. In the case of a connection with a pitch of 0.25 mm or less, even if solder is individually supplied to each pattern, the distance between adjacent portions is small, and a bridge is likely to be formed. Even in this case, if the solder has excellent melt separation property, the bridge disappears. Also,
Even when the paste and the solder foil (wire) are mounted on the pattern one character above, it is melted and separated by the pressure of the electrode, and it is confirmed that the solder of the present invention having excellent separability does not form a bridge. did.

Although no particular data is shown here, the above-described solder of the present invention (a solder having a composition in a region surrounded by ABCD in FIG. 6, or A'BB'C ') is used.
Solder having the composition in the area surrounded by D) and S
If b and Ag are added, the melt separability is further enhanced. The addition amount of Ag is 0 to 3 of the solder having the above composition.
It is preferable to add an amount of solder corresponding to wt%. As for Sb, 0 to 0.
It is preferable to add an amount of solder corresponding to 5 wt%.

[0059]

As described above, by using the solder of the present invention having an excellent melt separation property, even in the soldering of a narrow-pitch multi-pin LSI, the generation of a bridge which is inevitable with the conventional eutectic solder. Can be prevented. As a result, it is possible to eliminate the decrease in product yield due to the bridge. In addition, the number of steps such as correction can be reduced. Furthermore, since a large amount of solder can be printed when printing a solder paste, it is possible to prevent unsoldered solder.

[Brief description of drawings]

FIG. 1 is a model diagram showing an experimental method.

FIG. 2 is a diagram showing a size of a bridge.

FIG. 3 is a graph showing the relationship between the bridge size and the number of bridges of Sn63-Pb37 eutectic solder and Sn54-Bi1-Pb45.

FIG. 4 is a graph showing the relationship between the solder composition and the average bridge size of Sn—Pb based solder and Sn—Bi—Pb45 based solder.

FIG. 5 is a graph showing the relationship between the difference between the solid phase temperature and the liquid phase temperature and the average bridge size.

FIG. 6 is a state diagram showing a composition range of a Sn-Pb-Bi ternary solder according to the present invention.

FIG. 7 is a model diagram showing a metal mask and a substrate used in an experiment.

8 is a model diagram showing a state in which printing and mounting are performed using the metal mask and substrate of FIG.

FIG. 9 is a graph showing the relationship between the copper pad and the bridge ratio when reflowing in the state of FIG. 8 (a).

FIG. 10 is a graph showing the relationship between the copper pad and the bridge ratio when reflowing in the state of FIG. 8 (b).

[Explanation of symbols]

 1 ... Solder wire 2 ... Copper pad 3 ... Substrate 4 ... Solder 5 ... Size 2 bridge 6 ... Size 3 bridge 7 ... Eutectic line 8 ... Liquid phase temperature 175 ° C. line 9 ... Liquid phase temperature 200 ° C. line 10 … Metal mask 11… Bridge pattern 12… Solder paste 13… Paste short-circuit part 14… QFP 15… Lead

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical indication location C22C 13/00 (72) Inventor Hidee Shimokawa 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. Inside the laboratory (72) Inventor Toshihiro Yaya 1410 Inada, Hitachinaka City, Ibaraki Hitachi Ltd., Personal Media Equipment Division, Hitachi Ltd. System Division

Claims (10)

[Claims] 1. A solder having a surface tension smaller than that of a Sn-Pb eutectic solder and having a different solid-phase temperature and liquid-phase temperature. 2. The solder according to claim 1, which has a melting point of 170 ° C. or higher. 3. A Sn-Pb-based or Sn-Bi-Pb-based solder is surrounded by the following points A ', B, B', C ', D in the phase diagram of the Sn-Bi-Pb ternary alloy. Based on an alloy having a composition within the range, A ′ (Sn: 52 wt%, Pb: 48 wt%, Bi: 0
wt%) B (Sn: 48 wt%, Pb: 49 wt%, Bi: 3
wt%) B '(Sn: 48 wt%, Pb: 48 wt%, Bi: 4
wt%) C '(Sn: 54 wt%, Pb: 42 wt%, Bi: 4
wt%) D (Sn: 58 wt%, Pb: 42 wt%, Bi: 0
wt%). 4. A Sn-Pb-based or Sn-Bi-Pb-based solder having a composition within a range surrounded by the following points A, B, C and D in a phase diagram of a Sn-Bi-Pb ternary alloy is used. Based on the alloy having: A (Sn: 53 wt%, Pb: 47 wt%, Bi: 0 w
t%) B (Sn: 48 wt%, Pb: 49 wt%, Bi: 3 w
t%) C (Sn: 54 wt%, Pb: 42.5 wt%, Bi:
3.5 wt%) D (Sn: 58 wt%, Pb: 42 wt%, Bi: 0 w
t%) solder. 5. The solder according to claim 3, wherein Sb is contained in an amount corresponding to 0 to 0.5 wt% of the alloy. 6. The solder according to claim 3, wherein Ag is contained in an amount corresponding to 0 to 3 wt% of the alloy. 7. An electronic component, characterized in that a terminal portion of the electronic component is connected and fixed by using a solder having a surface tension smaller than that of a Sn-Pb eutectic solder and having a solid phase temperature and a liquidus temperature different from each other. Soldering method. 8. The solder as claimed in claim 2, 3 or 4
The method for soldering an electronic component according to claim 7, wherein the solder described in the above is used. 9. A plurality of electronic components and a solder to which terminals of the electronic components are connected and fixed are provided, and the solder has a surface tension smaller than that of Sn—Pb eutectic solder, and a solid phase temperature and a liquidus temperature. A mounting structure for electronic parts, characterized in that and are different from each other. 10. The electronic component mounting structure according to claim 9, wherein the solder according to claim 2, 3 or 4 is used as the solder.