JPS60141396A - Low-temperature solder alloy - Google Patents

Abstract

PURPOSE:To obtain a highly reliable low melting solder alloy which permits connection at a low m.p., has excellent thermal fatigue resistance of the solder itself and prohibits embrittlement of the alloy layer by adding a specific amt. of Bi, Pb and Sb thereto. CONSTITUTION:A low-temp. solder alloy is formed by adding 0.02-2.5wt% Sb to a compsn. consisting of 13-20wt% Bi, 42-50wt% Pb and the balance Sn. The solder alloy which permits joining at the m.p. of Sn-40wt% Pb or below in the through-hole part of electronic parts such as a printed circuit board, hybrid circuit board, etc. or plane packaging thereof and has particularly excellent thermal fatigue resistance is thus obtd.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention can be bonded to the through-hole portion or plane mounting of four-piece components such as printed circuit boards and hybrid circuit boards at a temperature below the melting point of Sn-40%Pb (183C). In particular, this relates to a solder alloy with poor thermal fatigue resistance.

[R scene of invention]

Generally, when assembling semiconductor components, J-connection is performed by passing all the leads through the through-holes of the printed circuit board and using wave soldering using eutectic solder of 5n-40 parts by weight Pb. However, as demand for mounting a wide variety of multi-functional single-layer parts on printed circuit boards has recently increased due to high-density mounting, hybridization, etc., self-blade blades have become difficult to remove and reinstall parts in the event of defects. 44-Considering that
If only 5n-40 heavy Arashi%Pb eutectic solder τ was used,
When parts are removed, adjacent joints are remelted, making it impossible to maintain high reliability. Therefore, the conventional 5n-4
In combination with 0ji Meng%Pb solder, it was necessary to use a solder that could be connected by one person and whose reliability, especially thermal fatigue resistance, of the soldered joint was equal to or better than that of the eutectic type. . Therefore, low melting point solder with excellent thermal fatigue resistance (
Bi 13-20% by weight, Pb 42-50% by weight, balance S
Japanese Patent Application No. 57-101254] has been proposed.

However, since the above-mentioned solder stretches and collapses when squeezed, the heat fatigue resistance of the solder blank is excellent, but when applied to through-hole joints on printed circuit boards, the alloy layer formed on the phosphorus*copper lead It was found that embrittlement caused by growth V becomes a problem. Therefore, it became necessary to prevent the alloy layer from becoming brittle.

[Purpose of the invention]

The purpose of the present invention is to enable bonding at a low melting point temperature, to improve the thermal fatigue resistance of the solder itself, and to prevent embrittlement of the alloy layer.
) Our goal is to provide high-quality low melting point solder alloys.

[Summary of the invention]

The solder alloy of the present invention has a weight ratio of B113 to 20%, P
b42-50%, remaining 2nK, Cb 0.02-2.5%
It consists of a composition with a sprinkling. Preferably, in terms of weight ratio, B is around 118%, Pb is around 45%, and the balance is S.
In the composition of n, Sb is 0.02 to 2. s % of added bile.

Figure 1 shows Pb when gold is 18% (constant).
It shows 1lIt of squeeze against the amount, 5n-18
%Bt-45%Pb solder has excellent drawing properties, so the thermal fatigue resistance of the solder itself is S n-13i -p
This is the most worrying composition among the b series (Japanese Patent Application No. 57710)
1254). By adding Sb to this excellent composition, a brittle alloy 4 (
It was found that it has the effect of suppressing the growth of Cu3Sn. Since the addition of sb is a pretense, it only slightly increases the strength of the raw material itself, but does not significantly change it. Namely 1. The thermal fatigue resistance of the d-bonded material itself is slightly reduced. On the contrary, the embrittlement of the IT layer is reduced.

FIG. 2(a) shows the progress of crack 2 after the first temperature cycle test (-650-125C) in the case where the phosphorus # copper lead 3 is bonded to the through hole of the print plate 5 by solder. Cracks occur on the Cu plating side 4 and the lead side, but especially on the Cu3f3n alloy layer 6 on the S/# steel side.
There is great progress between copper and phosphorus. 7 in FIG. 2(b) is a Cu6Sna alloy layer, and the properties of this alloy are good, with few cracks occurring.

In the process of forming the alloy layer, first, C'6S"5 is formed, and after a long period of time at high temperature, 7'LCu 3 S n phosphorus #M4 (or Cu plating) ll+!l is formed. Therefore, The effect of Sb addition is thought to be to completely inhibit the growth of the deposited alloy layer, and to inhibit the growth of Cu and F3n.

[Embodiments of the invention]

Sn 18WIXBi 45Wt
．． 1.0.2°, 0.5, and 1.3% were added to each solder, and each solder was soldered onto a through-hole board to create a through-hole joint. The soldering conditions were to immerse the board in barley preheated to 100G at 180C for 15 seconds. The flux used is a rosin type. Solder composition t
- Each of the different test strips has 910 through holes per substrate. This test piece was heated to 65C = 125C
, 4hloc temperature cycle tank, and after 200oc, the development of cracks was fully checked. Crack progression is on the board/
41 Coefficient of thermal expansion in the transverse direction (xloxto-'/C),!
:, l) - thermal 1 m tensile modulus (17,5X 10-'
/C). Less crack growth means better thermal fatigue resistance. Figure 3 shows the cross section of the test piece after temperature cycling. L, the crack length was measured under a microscope, and the ratio to the thickness of the through hole was plotted on the vertical axis. According to Figure 3, in the 12 cases of Sb addition, o, 'o i wt%, and 3 wt% addition.
It can be seen that the growth of the crank is remarkable when the fcJa is 2. The reason for this is that when the amount of Sb splicing is small, 42
As shown in the figure, <Cu5p" is widely generated on the phosphorus tn side. When Sb added violet exceeds 3wt%, the solder becomes hard and brittle, so the rigidity of the solder, which is susceptible to crack growth, cannot be ignored. (Caused by mechanical deterioration of solder) 2 Ivy increases.

It can be seen from FIG. 4 that the growth of alloy No. decreases with Sb-added iron f JVIy. Reducing the Sb content to some extent reduces the formation of alloy particles and alleviates the deterioration of the alloy layer interface, and also increases the resistance of the solder itself, improving overall thermal fatigue resistance. will improve.

〔Effect of the invention〕

According to the present invention, 811-37 wt% of pb-8n eutectic system
It has become possible to connect Pb (melting point 183C) without bath-melting it, and it has thermal fatigue resistance.

[Brief explanation of drawings]

Figure 1 is a custom-made mechanical diagram of a ternary system (5n-P''b-B i) low ifi point l reader, and Figure 2 is a through-hole diagram of a printed board.
Diagram showing a model of the development of taratsuta around hole 4, No. 31A
yj Sb Princess ij Diagram showing the relationship between mouth void and crack length,
-34 is a diagram showing the thickness of the IA yarn τ of the Sb hemp layer and the laminar layer. Work...ν read, 2...crack, 3...lead, 5...pu Figure 1 (wt finish) Run length finish 1 5 Thread addition amount (wtE)

Claims (1)

[Claims] 1, B113-20% by weight, Pb42-b%, balance Sn
A low-crystalline solder alloy with a good composition and 0.02 to 2.5% Sb added.