JP3365158B2 - Terminal treatment method for electronic components and connection terminals - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to connection terminals (for example, leads) preliminarily soldered with eutectic solder or the like when surface-mounting large-scale integrated circuit elements and electronic components on a circuit board with lead-free solder. Part) and the like, the present invention relates to a method of treating a terminal of an electronic component in which the solder coating material is replaced with lead-free solder, and a connection terminal treated by the method.

[0002]

2. Description of the Related Art A surface coating method of a solder coating material for connecting terminals, which plays an important role in surface mounting a large scale integrated circuit element or electronic component on a circuit board by soldering, has a poor solderability. It is intended to improve the solderability by coating the base material of the solder coating material with a material having a better solderability.

When the connection terminals are coated with a solder alloy used for mounting, so-called preliminary solder is formed. Good solderability is necessary to ensure the reliability of the product by making the mechanical strength of the joint sufficient.

The preliminary solder is formed by electroplating or hot dipping. Most of the solders commonly used in the electronics industry today are alloys of tin Sn and lead Pb and are represented by the composition symbol 63 wt% Sn and 37 wt% Pb. Wt% Sn and approximately 39.1 wt% Pb, melting point 183 ℃), and is "ROKUYON solder"
The composition symbol will be abbreviated as Sn-37Pb including the composition of the regular tin-lead eutectic solder.

Recently, in Europe and the United States, movements to regulate lead contained in solder for electronics have become active from the viewpoint of environmental pollution. In response to this movement, lead-free solders, so-called lead-free solders, are being actively developed.

Lead-free solder alloys currently being developed are roughly classified into the following two types. (B) A solder alloy with a melting point (183 ° C or less) lower than that of Sn-37Pb, including In-48Sn (melting point 117 ° C), Bi-43Sn (melting point
139 ℃) based. (B) A solder alloy with a higher melting point (183 ° C or higher) than Sn-37Pb, Sn-3.5Ag (melting point 221 ° C), Sn-9Zn (melting point
199 ℃) based.

In order to put the lead-free solder into practical use, the soldering temperature is maintained at the current level (215 ° C to 230 ° C). That is, it is considered very important to make the melting point of the solder alloy equal to or lower than the melting point (183 ° C) of the Sn-Pb eutectic solder.

This is because almost all of the premise is to use Sn-Pb eutectic solder when evaluating the influence of thermal stress during soldering on reliability, and also for components used in electronic equipment. However, it tends to be small, lightweight, and inexpensive, and the heat resistance problem of parts has come to be greatly highlighted with this trend.

In—Sn and Bi—Sn based low melting point lead-free solders have no problem in terms of melting point. With these alloys, the soldering temperature can be lower than before,
In addition to lead-free solder, there are advantages such as elimination of baking treatment and post-treatment, and use of low heat-resistant parts to reduce costs.

On the other hand, in high melting point lead-free solder, an attempt has been made to lower the melting point by adding a low melting point metal. Low melting point metals include In, Bi, Hg, Cs, Ga, Rb,
Although K, Na, Li, Tl, Cd, etc. are considered, they are difficult to apply to electronic devices because they are highly toxic except In and Bi and are alkali metals. Add In, Bi
The melting points of Sn-Ag series and Sn-Zn series are the same as those of Sn-Pb eutectic solder 1
In order to reach about 83 ° C., it is necessary to add 10% or more of In or Bi.

[0011]

However, a serious problem arises here. Lead-free solder is pre-soldered when connecting terminals, which are pre-soldered with Sn-Pb eutectic alloy, which is popular all over the world, to lead-free solder containing Bi or In at required places such as printed wiring boards. By diffusing inside, it moves to the connection terminal side, the amount of solder in the soldered portion is reduced, and the joint strength is greatly reduced. Moreover, a ternary alloy of Sn-Pb-In and Sn-Pb-Bi is partially generated, but this ternary alloy has a low melting point (solidus temperature).
In the thermal shock test at 65 ° C to + 125 ° C, melting and solidification are repeated, and finally, the phenomenon of peeling from the solder surface is caused, which causes a problem that the joint strength after the thermal shock test is reduced.

[0012] Japanese Patent Application Laid-Open No. 4-2879
There is an invention of "a jig and a method for removing a lead gold plating layer of an LSI package" disclosed in No. 57. This content is because the gold plating layer at the tip of the lead is hard and brittle when soldered with a solder containing tin, a binary metal compound AuSn _x is generated between the gold on the lead surface and tin contained in the solder, and In order to significantly reduce the temperature, a method of removing the gold plating by dipping the gold plating layer in the molten solder for a certain time is disclosed. However, a solution to the problem of reduction in joint strength caused by diffusion and ternary alloys that occur when soldering lead wires coated with tin-lead eutectic solder other than gold plating with solder that does not contain lead Is not shown.

Originally, it is preferable that the pre-solder has the same composition as that of the solder to be used, and in practical application of the lead-free solder, it should be considered on the assumption that the parts pre-soldered with the developed lead-free solder alloy are used. However, the suppliers and producers of parts are very diverse and diverse at present, and it is expected that there will be a considerable time lag before all of these manufacturers and producers comply with the lead regulations, and the regulations will not be implemented. Or, there is a possibility that some producing countries will move very slowly.

As a result of consideration from this point of view, when lead-free solder is used, it can be said that a situation in which the Sn-Pb eutectic alloy is pre-soldered on the component to be mounted can naturally occur. As a result, the above-mentioned problem of reduction in bonding strength due to diffusion and generation of ternary alloy becomes a serious problem.

The main object of the present invention is a low melting point, lead-free solder alloy that does not cause diffusion or ternary alloy during soldering of pre-solder such as connection terminals whose surface is coated with eutectic solder or the like. It is an object of the present invention to provide a method of substituting the same with a solder connecting terminal treated by the substituting method.

[0016]

[Means for Solving the Problems] The above-mentioned problems are caused by a solder having an alloy composition containing no lead having a low melting point after the removal of the surface-treated preliminary solder on the connection terminals of the electronic component before soldering. It can be solved by replacing. Hereinafter, a method of replacing the pre-solder surface-coated on the connection terminal of the electronic component and the connection terminal processed by the replacement method will be described.

According to a first aspect of the present invention, there is provided a method of treating a terminal of an electronic component, wherein the connecting terminal of the electronic component whose surface is coated with the preliminary solder has an alloy composition lower than the melting point temperature of the preliminary solder and containing no lead. It is characterized in that it is immersed in a solder bath and the solder of the pre-soldered connection terminal is thermally diffused and replaced with the solder in the solder bath.

If the lead-free alloy composition used at the time of mounting is directly soldered to the preliminary solder coated on the surface of the connection terminal, the diffusion strength and the generation of the ternary alloy cause a decrease in the soldering strength. However, by immersing the connection terminals whose surface is coated with pre-solder in a solder bath in which an alloy composition not containing lead is melted, when the melting temperature of the solder bath is lower than the liquidus temperature of the pre-solder. The presolder is removed from the connection terminals by thermal diffusion rather than melting in the solder bath and is surface coated with the lead-free solder alloy in the solder bath instead of the presolder.

According to a second aspect of the present invention, there is provided a terminal treatment method for an electronic component according to the first aspect, wherein the preliminary solder has a composition corresponding to a eutectic solder of tin and lead, and the preliminary solder is Sn. , Bi, Ag, Zn, In, Cu, or Sb is replaced with a lead-free solder whose main component is.

According to the first aspect of the present invention, there is provided a method of treating a terminal of an electronic component, wherein the pre-solder material coated on the surface of the connection terminal is a eutectic solder equivalent of tin and lead which is most popular nowadays. By replacing the pre-solder with a non-toxic lead-free solder containing at least one of the metals as a main component by the method described in 2, the removal of the lead-containing solder and the replacement with another lead-free solder can be performed simultaneously. There is.

The terminal processing method for an electronic component according to claim 3 of the present invention, the connection terminals of an electronic component formed by surface coating by preliminary soldering, by the preliminary soldering is treated with liquid to be eroded, pre Ki予 After removing the prepared solder, the solder is replaced with a solder having an alloy composition containing no lead .

As a pre-soldering method other than the first or second aspect of the present invention, a connection terminal to which pre-soldering is applied,
Even with the method of removing the preliminary solder by treating it with a liquid that corrodes and then immersing it in a solder bath of an alloy composition containing no lead and replacing it in a two-step process, diffusion and generation of a ternary alloy are prevented during soldering. it can.

The connection terminal according to claim 4 of the present invention is characterized by being processed by the terminal processing method for an electronic component according to claim 1, 2 or 3. Claims 1 and 2
Or, the connection terminals treated by the method for treating terminals of electronic components described in 3 realizes non-toxic lead-free solder coating, eliminates baking treatment and post-treatment, and can reduce cost by using low heat resistant components. Has the effect of.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below. The connection terminals of large-scale integrated circuit elements and electronic components that are surface-coated with preliminary solder are dipped in a bath of molten solder that has a low melting point alloy that does not contain lead, and the preliminary solder is placed in the solder bath. The method of replacing the pre-solder of the connection terminal with the lead-free solder by heat-diffusing to the lead-free solder is to control the parameters such as solder temperature, dipping time, dipping speed, pulling speed, etc. .

It is also possible to prevent a bridge between leads when the connecting terminal is composed of a large number of pins. The surface shape of the connection terminal is also a parameter that affects the coating of the pre-solder after replacement, but by adjusting other parameters according to the surface shape, it is possible to prevent variations in the coating of the pre-solder depending on the type of the surface shape.

Depending on the degree of corrosion or oxidation of the surface of the preliminary solder, the flux for flow soldering or the like is applied and then dipped in a solder bath having a lead-free solder alloy composition to coat the preliminary solder. It is preferable to improve the substitution efficiency.

In the present invention, the temperature of the solder bath having an alloy composition not containing lead is preferably about 30 ° C. + the melting temperature of the solder alloy in the solder bath. This allows
Removal and replacement by sufficient thermal diffusion are possible at the same time. Therefore, the thermal stress applied to the connection terminal and the components in the vicinity thereof can be adjusted to be equal to or lower than the temperature during soldering.

Contamination due to the composition of the preliminary solder diffused in the solder bath in which the lead-free alloy composition to be replaced is melted is caused by increasing the size of the bath depending on the amount of immersion of the connection terminal coated with the preliminary solder in the solder bath. Suppress the diffusivity below the required value by increasing the amount of solder in the bath, by increasing the number of solder baths to regulate the number of dipping connection terminals per bath, or by using both together. Therefore, it is preferable to control the diffusion reaction and the generation of the ternary alloy, thereby preventing the reduction of the bonding strength.

The preliminary solder material coated on the connection terminals is
Substitution of lead-free solder with other lead-free solder by replacing this preliminary solder with lead-free solder by the above dipping method when it is equivalent to the most commonly used eutectic solder of tin and lead at present A method of processing connection terminals that can be executed simultaneously is realized.

In this case, the lead-free solder component to be replaced is
If 58Bi-42Sn (melting point temperature 139 ° C) and eutectic solder of tin and lead 63Sn-37Pb (eutectic temperature 183 ° C) are used as the components of the pre-solder, the pre-solder is a lead-free solder bath lower than the eutectic temperature. The preliminary solder is sufficiently replaced with lead-free solder by thermal diffusion rather than melting by immersion.

As another method of removing the preliminary solder, there is a method of removing the connection terminal to which the preliminary solder is applied by treating it with a liquid that corrodes the preliminary solder. Liquids that attack the presolder can include acids or alkalis over a wide range. In the case of strong acid or strong alkali, it is necessary to optimize the conditions such as liquid composition, composition temperature, treatment time, etc. so as not to erode the base material of the connecting terminal and the package resin. Organic acids such as acetic acid, oxalic acid, and propionic acid can selectively erode the alloy coated on the connection terminals as a pre-solder to remove it.

In the case of the pre-soldering agent containing an organic acid as a main component, by adjusting the composition of the solvent, it is possible to further enhance the contact property and the contact directivity with respect to the solder alloy to be easily removed. As a result, only the preliminary solder is selectively infiltrated without eroding the base material of the connection terminal or the package resin,
Can be removed.

The surface of the base material of the connection terminal from which the preliminary solder has been removed is cleaned, and if it is for a short time after the removal, a considerable solderability can be expected without surface coating. If you want to increase the time from the removal process to soldering, or if you want to ensure sufficient solderability, pre-solder the lead-free alloy composition again after the removal process to replace the pre-solder of the connection terminal. It becomes possible in a stepwise process.

Next, the preliminary solder replacement effect of the connection terminal of the present invention will be proved by experimental results. Three 58Bi-42Sn solder baths (soldering amount 200g) were prepared, and 63Sn-37Pb was pre-soldered in them. SOP (small outline package; abbreviated as gull wing lead type)
Abbreviated as pins and the like. The lead part of 1) was immersed in each bath for 1 minute. The alloy composition of the lead was measured by electron spectroscopy analysis and X-ray fluorescence analysis, and the composition of 63Sn-37Pb
It was confirmed that it could be replaced with Bi-42Sn.

This SOP was soldered to a Cu pad on a glass / epoxy substrate with 58Bi-42Sn solder paste, and a thermal shock test (-50 to 125 ° C., 200 cycles) was conducted. When the joint strength was measured by a tensile test, the joint strength did not change before and after the thermal shock test, and the effect of replacement of the preliminary solder was confirmed as shown in the table below.

[0036]

[Table 1] As a comparative example, Sn-37Pb S without replacing the preliminary solder
When a similar test was conducted in OP, as shown in Table 1,
It was confirmed that the joint strength before the thermal shock test was lower than that of the substituted one, and that the joint strength was greatly reduced after the thermal shock test.

Further, the lead of SOP14 pin, which is pre-soldered with 63Sn-37Pb, is pre-soldered with a remover containing 10% acetic acid, 70% xylene, and 20% isopropyl alcohol at 50 ° C. for 24 hours.
Let it soak for an hour. The results are analyzed by electron spectroscopy and fluorescence X
63Sn-37Pb by measuring the alloy composition of the lead by line analysis
Was confirmed to have been removed. After that, 58Bi-42Sn
Immerse the lead part in the solder bath of
58Bi-42Sn was coated. When the above thermal shock test was conducted using this SOP14 pin, the same substitution effect as the above immersion substitution method was obtained.

[0038]

EFFECT OF THE INVENTION By using the pre-soldering method of the present invention, the problem of reduction in joint strength that occurs when the composition of the solder alloy of the solder paste used at the time of mounting and the pre-soldering of the connection terminal of an electronic component is different is solved. can do.

Since this method can be automated with a simple and inexpensive apparatus, the cost increase due to the increase in the number of steps can be suppressed to a low level.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-7-65878 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05K 3/34 B23K 1/20 B23K 35 / twenty four

Claims (4)

(57) [Claims] 1. A connection terminal of an electronic component, which is surface-coated with preliminary solder, is dipped in a solder bath having an alloy composition lower than the melting point temperature of the preliminary solder and containing no lead, and the pre-soldered connection terminal is A method of treating a terminal of an electronic component, characterized in that the solder is thermally diffused and replaced with the solder in the solder bath. 2. The pre-solder has a composition corresponding to a eutectic solder of tin and lead, and the pre-solder comprises Sn, Bi, Ag, Zn, In,
2. The terminal processing method for an electronic component according to claim 1, wherein the lead-free solder containing at least one of Cu and Sb as a main component is substituted. The 3. A connecting terminal of an electronic component formed by surface coating by preliminary soldering, by the preliminary soldering is treated with liquid to be eroded, before after removing Ki予 Bei solder containing lead <br/> A terminal treatment method for an electronic component, characterized in that it is replaced with a solder having a non-alloy composition. 4. A connection terminal processed by the method of processing a terminal of an electronic component according to claim 1.