JPH0952191A - Solder alloy and solder paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solder alloy excellent in Ag erosion resistance and thermal fatigue resistance. SOLUTION: A solder has a composition consisting of, by weight, 50-70% Sn, 0.5-5.0% Ag or total quantity of Ag and In, 0.1-2.0% Bi, 0.03-0.3% Cu, 0.1-2.0% Sb and the balance Pb 0.002-0.5 pts.wt. P is added to 100 pts. wt. the composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder alloy and a paste-like solder using a powder of the solder alloy.

[0002]

As is well known, when soldering, when the metal to be soldered is melted into molten solder and the solder is solidified,
A phenomenon in which a compound of Sn or Pb of a solder component and a metal to be soldered is deposited, that is, solder corrosion is unavoidable, and so-called Ag erosion may occur. For example, when mounting an electronic component on a circuit board, Ag is dissolved in molten solder during soldering to an Ag thick film electrode, etc., and the compound of Ag and Sn or Pb is deposited at the soldering interface. There is. In this case, there is a fear that Ag thick film electrode may disappear due to Ag erosion, leading to conduction failure and the like. Therefore, various compositions of Ag corrosion preventing solder have been proposed.

As is well known, at the soldering interface,
Occurrence of thermal stress due to the difference in coefficient of thermal expansion between the solidified solder and the metal to be soldered is unavoidable. Especially under heat cycle, the stress becomes repetitive stress and causes fatigue at the soldering interface. Becomes Therefore, various solder compositions have been proposed for improving fatigue resistance. In particular, a circuit board on which electronic components are mounted undergoes a heat cycle due to turning on and off of energization, so that not only the Ag corrosion resistance described above but also a high degree of thermal fatigue resistance is required.

In order to prevent the above Ag corrosion, Ag is added to the solder.
Is effective in adding an amount equivalent to the saturation concentration at the soldering temperature.
A composition is known in which 0.5 to 5.0% by weight of Ag is added to n-Pb solder. In this case, the effectiveness of adding Ag and In instead of adding Ag alone is also known. However, addition of Ag or Ag and In alone is not sufficient to impart heat fatigue resistance, and in order to improve not only Ag corrosion resistance but also heat fatigue resistance, for example, the following composition is proposed. ing.

(1) Sn: 15 to 65% by weight, Ag:
0.5-3.5% by weight, Sb: 0.5-3.0% by weight,
Remainder Pb (JP-A-56-144893). (2) Pb: 10 to 95% by weight, Ag: 0.01 to 10
%, In: 0.01 to 10% by weight, Sb: 0.1
8% by weight, balance Sn (JP-A-3-106591). (3) Pb: 10 to 95% by weight, Ag: 0.01 to 10
Wt%, In: 0.01 to 10 wt%, Bi: 0.1
8% by weight, balance Sn (JP-A-3-106591). (4) Pb: 20 to 35% by weight, Ag: 0.05 to 5% by weight, In: 0.1 to 5% by weight, Sb: 0.05 to 1% by weight, Cu: 0.05 to 2% by weight , Balance Sn (JP-A-3
-106591). (5) Pb: 35 to 50 wt%, Ag: 0.05 to 5 wt%, In: 0.1 to 5 wt%, Sb: 0.05 to 1 wt%, Cu: 0.05 to 2 wt% , Balance Sn (JP-A-3
-106591). (6) Pb: 10 to 90% by weight, Ag: 0.05 to 4.
0% by weight, Sb: 0.5 to 5.0% by weight, Cu: 0.0
5 to 3.0% by weight, balance Sn (Japanese Patent Publication No. 52-30377)
Issue).

[0006]

These solder compositions have a composition of Sn-Pb solder to Ag, Bi, In, Sb, Cu.
Of Ag, Bi, I
Not all of n, Sb, and Cu are added. Ag,
It is known to use Bi, In, Sb, Cu, etc. as an additive for Sn—Pb based solder (see, for example, Japanese Patent Laid-Open Publication No. Sho 6-62).
(Table 1 of JP-A-1-273292), the above (1) to
The solder composition illustrated in (7) is Ag, Bi, In, S.
By selecting 3 or 4 kinds of b and Cu and limiting the addition amount thereof, Ag corrosion resistance and thermal fatigue resistance are improved. In any composition, Ag or Ag and In are added to impart Ag corrosion resistance.

However, none of them contain Bi, Sb, and Cu together. Bi, Sb, Cu, etc. contribute to the improvement of thermal fatigue resistance in that the structure of the solder itself is densified to increase the mechanical strength. However, densification of the structure raises the melting point of the solder, and when the melting point rises, the dissolved saturation concentration of Ag rises.
Corrosion is likely to occur, and eventually thermal fatigue resistance cannot be guaranteed. However, the thermal fatigue resistance can be improved also by increasing the bonding strength by forming a stable alloy layer at the bonding interface and imparting the elongation property to the solder itself, and according to the study result of the present inventor, Bi, Sb, Cu Addition of the above three together in a specific amount makes it possible to improve not only the mechanical strength of the solder but also the thermal fatigue resistance from these points, and it is possible to effectively prevent Ag corrosion and to provide excellent thermal fatigue resistance. I knew that I could add sex.

The object of the present invention is to improve anti-A
g It is to provide a solder alloy which is excellent not only in corrosion resistance but also in heat fatigue resistance.

[0009]

The solder alloy according to the present invention contains 50 to 70% by weight of Sn, Ag or Ag and In.
Of 0.5 to 5.0% by weight and Bi of 0.1 to 2.
0% by weight, Cu 0.03 to 0.3% by weight, Sb 0.
1 to 2.0% by weight, and the balance is Pb, and 100 parts by weight of the composition has 0.05% P.
It is also possible to add 02 to 0.5 parts by weight. The paste solder according to the present invention is composed of this solder alloy powder and the paste flux.

In the present invention, a Sn--Pb alloy is used as a base.
The reason for using the solder is to ensure wettability, which is a basic condition for soldering. The reason for setting the amount of Sn to 50 to 70% by weight is to set the liquidus temperature to a soldering temperature suitable for the flow method or the reflow method, so that the surface mount component can be protected from thermal shock damage. It is an effective requirement for safe soldering and for effectively preventing Ag corrosion by eliminating the increase in saturation solubility of Ag.

The reason for adding Ag is to prevent the above-mentioned Ag corrosion, and the reason for adding 0.5 to 5.0% by weight is that the effect is less than 0.5% by weight. If it cannot be satisfactorily achieved, and if it exceeds 5.0% by weight, the liquidus temperature becomes too high, and the saturated solubility of Ag increases, so that the effective Ag
This is because it is difficult to prevent corrosion, and it is difficult to set the appropriate soldering temperature. The reason for using Ag and In instead of adding Ag alone is that Ag is added by adding Ag.
₃ Sn whiskers - is because the occurrence of is concerned, in this case, the In amount is more than 5.0 wt%, heat for solid phase transformation at low temperature range - weakening of tissue by preparative cycle Is caused, and it becomes difficult to guarantee heat fatigue resistance.

The reason for adding Bi is to promote the densification of the alloy structure and to increase the mechanical strength. The reason for adding Bi in the range of 0.1 to 2.0% by weight is 0.1% by weight. %
If it is less than 2.0% by weight, the effect cannot be satisfactorily achieved. If it exceeds 2.0% by weight, the viscosity of the solder itself is reduced, the elongation is reduced and the solder becomes brittle, and it becomes difficult to guarantee heat fatigue resistance. This is because the sex is lost.

The reason for adding Cu is to increase the mechanical strength in the same manner as described above.
The reason why the content is 0.3% by weight is that the effect cannot be satisfactorily achieved when the content is less than 0.03% by weight,
The melting point becomes high and it becomes difficult to set the appropriate soldering temperature, etc., and the mechanical strength of the solder decreases, and it becomes difficult to guarantee the thermal fatigue resistance, and further, the fluidity of the solder decreases. This is because workability becomes poor.

The reason for adding Sb is to increase the mechanical strength as well as to increase the joint strength of the solder, as described above. The reason for adding Sb is 0.1 to 2.0% by weight. If the amount is less than 0.1% by weight, the effect cannot be satisfactorily achieved. If the amount exceeds 2.0% by weight, the solder itself becomes hard and brittle, the elongation is reduced, the joint strength is reduced, and the guarantee of heat fatigue resistance is ensured. This is because it becomes difficult, or the fluidity of the dangling drops and the workability deteriorates.

The action described in relation to the reason for adding Ag, Ag and In, Bi, Sb and Cu and the amount added is the action which is achieved by each additive element alone. From the comparison between the following examples and comparative examples, it can be recognized from the fact that the heat fatigue resistance remarkably deteriorates even if any element is deleted.

In the present invention, the reason for adding P is to prevent oxidation and to suppress deterioration of wettability and spreadability due to addition of Cu or Sb. The reason for adding P to 0.002 to 0.5% by weight is as follows. If it is less than 0.002% by weight, the effect cannot be satisfactorily achieved, and if it exceeds 0.5% by weight, the solder itself becomes hard and brittle, the elongation decreases, and it becomes difficult to guarantee the thermal fatigue resistance.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The solder alloy according to the present invention exhibits excellent thermal fatigue resistance as compared with conventional solder. In addition to the above additive elements, JIS-Z-328
Even if the impurities within the range of Class A defined in 2 are included, the effect of the present invention is achieved without being affected. The solder alloy according to the present invention is used for mounting electronic components on a circuit board by a flow method. It is also used for mounting electronic components on circuit boards by the reflow method.In this case, the electronic components are temporarily fixed to the circuit board by the adhesive force of the paste-like solder, and this circuit board is passed through a heating furnace. Soldering is performed by reflowing the paste solder. In the paste solder according to the present invention, the solder powder 85
.About.95% by weight, the balance is used in a paste-like flux, and the solder powder mesh is set to 250 to 500. To the paste-like flux, an activator such as cyclohexylamine HBr, octylamine HBr, malonic acid, succinic acid, benzoic acid, etc. is added to rosin such as polymerized rosin, hydrogenated rosin, natural rosin, and maleated rosin. It is possible to use a paste prepared from this with a solvent. The solder alloy according to the present invention may be used in the form of the above-mentioned powdery, rod-shaped, linear, ribbon-shaped, or flux cored solder.

[0018]

【Example】

[Example 1] In the composition of the solder alloy, Sn: 62% by weight,
Ag: 2.0 wt%, Bi: 0.6 wt%, Cu: 0.
06% by weight, Sb: 0.6% by weight, and the balance Pb was used. For the paste-like flux, polymerized rosin: 60% by weight, hydrogenated castor oil: 5% by weight, cyclohexylamine HBr: 1% by weight, balance butyl carbitol was used. A paste-like solder was prepared by mixing and stirring 10% by weight of the paste-like flux.

[Example 2] In comparison with Example 1, Ag: 2.
A paste-like solder was prepared in the same manner as in Example 1 except that Ag: 1.0% by weight and In: 1.0% by weight were used instead of 0% by weight. [Example 3] A paste-like solder was prepared in the same manner as in Example 1 except that an alloy composition obtained by adding 0.1 parts by weight of P to 100 parts by weight of the solder alloy composition of Example 1 was used. [Example 4] A paste-like solder was prepared in the same manner as in Example 2 except that an alloy composition obtained by adding 0.1 parts by weight of P to 100 parts by weight of the solder alloy composition of Example 2 was used.

Comparative Example 1 Compared to Example 1, the same procedure as in Example 1 was carried out except that the solder alloy composition was Sn: 62% by weight, Ag: 2.0% by weight, and the balance Pb. Stroke-shaped solder was created (Bi, Cu, and Sb were omitted from Example 1). [Comparative Example 2] In comparison with Example 1, the composition of the solder alloy is S
A paste-like solder was prepared in the same manner as in Example 1 except that n: 62% by weight, Ag: 2.0% by weight, Bi: 0.6% by weight, and the balance Pb was used (versus Example 1). , Cu and Sb omitted). [Comparative Example 3] Compared to Example 1, the composition of the solder alloy was changed to S.
n: 62% by weight, Ag: 2.0% by weight, Cu: 0.06
A paste-like solder was prepared in the same manner as in Example 1 except that the weight% and the balance Pb were used (Bi and Sb were omitted from Example 1). [Comparative Example 4] Compared to Example 1, the composition of the solder alloy was changed to S.
A paste-like solder was prepared in the same manner as in Example 1 except that n: 62% by weight, Ag: 2.0% by weight, Sb: 0.6% by weight, and the balance Pb was used (versus Example 1). , Bi and Cu omitted). [Comparative Example 5] In comparison with Example 1, the composition of the solder alloy was S
n: 62% by weight, Ag: 2.0% by weight, Bi: 0.6% by weight, Cu: 0.06% by weight, except that the balance Pb is used,
A paste solder was prepared in the same manner as in Example 1 (Sb is omitted from Example 1). [Comparative Example 6] Compared to Example 1, the composition of the solder alloy was changed to S.
n: 62% by weight, Ag: 2.0% by weight, Bi: 0.6% by weight, Sb: 0.6% by weight, and a paste solder was used in the same manner as in Example 1 except that the balance Pb was used. It was created (Cu is omitted as compared with Example 1). [Comparative Example 7] Compared to Example 1, the composition of the solder alloy was changed to S.
n: 62% by weight, Ag: 2.0% by weight, Cu: 0.06
% By weight, Sb: 0.6% by weight, except that the balance Pb is used,
A paste-like solder was prepared in the same manner as in Example 1 (Bi is omitted from Example 1). In any of the above alloy compositions, impurities other than the additive elements are contained in JIS-Z-328.
It belongs to the class A range specified in 2.

Using the paste-like solders of these Examples and Comparative Examples, the chip resistors were soldered to the glass epoxy circuit board by the reflow method, and the solder was applied at -40 ° C. for 30 minutes.
Min., A thermal shock test at 100 ° C. for 30 minutes as one cycle was performed up to 500 cycles, and the appearance of the soldering fillet was observed every 100 cycles during that time, and the results are shown in the table. However, ◯ indicates that the soldering fillet is normal, Δ indicates that wrinkles are generated, and × indicates that cracks are generated.

[0022]

[Table 1]

As is clear from this table, according to the present invention, the durability of the soldering fillet against repeated thermal stress can be dramatically improved. Particularly, compared to Comparative Example 5 in which Sb was omitted, Comparative Example 6 in which Cu was omitted, and Comparative Example 7 in which Bi was also omitted, a significant improvement effect was recognized, and thus Bi and Cu were An unexpected synergy with Bi is speculated.

[0024]

According to the present invention, it is possible to provide a solder alloy and a paste-like solder capable of remarkably stable soldering with respect to a thermal shock test, and to improve the continuity reliability and stability of electronic component mounting circuit boards. Can be guaranteed for a long time.

Claims (3)

[Claims] 1. Sn is 50 to 70% by weight, Ag or Ag.
And the total amount of In are 0.5 to 5.0% by weight, and Bi is 0.
1 to 2.0 wt%, Cu 0.03 to 0.3 wt%, S
A solder alloy characterized in that b is 0.1 to 2.0% by weight and the balance is Pb. 2. A solder alloy in which 0.002 to 0.5 parts by weight of P is added to 100 parts by weight of the composition according to claim 1. 3. A paste-like solder comprising the solder alloy powder according to claim 1 and a paste-like flux.