JPH07155980A - Joining method - Google Patents

Abstract

PURPOSE:To realize the excellent wettability and high heat resistance of the solder or the brazing filter metal at the same time during the joining operation. CONSTITUTION:First and second solders 4, 5 whose melting point is different are laminated to realize the double coating by approximately same amount on the outer surface of a member 1 to be joined by making the first solder 4 where the melting point is high and the heat resistance is high as the inner layer, and the second solder 5 where the melting point is lower and the wettability is excellent. After the member 1 to be joined is temporarily fixed by bringing the coated surface of the second solder 5 into contact with the joining surface 3, the second solder 5 is melted by the low temperature heating through the reflow. After the second solder 5 is melted, the first solder 4 is melted by the high temperature heating, and the first and the second solders 4, 5 are mixed to join the member 1 to be joined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joining method for joining members to be joined which are coated with heat resistant solder or brazing material with good wettability.

[0002]

2. Description of the Related Art As an example of a joining method, soldering means by reflow will be described below with reference to FIGS.
Prior to soldering, first, the members to be joined such as chips (1)
The solder material (2) is temporarily fixed to the outer surface of the above, melted and cured, and the outer surface of the joined member (1) is once covered with the solder material (2). Therefore, the member to be joined (1) is placed on the joining surface (3) and radiantly heated by irradiating infrared rays, laser light, warm air or the like at a predetermined temperature, or the member to be joined (1) is conducted by a heater. When heated, the solder material (2) melts and wets the joint surface (3), so that the member to be joined (2) is joined to the joint surface (3).

Here, the solder material (2) is an alloy in which lead (Pb) and tin (Sn) are mixed at a predetermined mixing ratio (wt%), and the Sn-Pb type solder of FIG. 2 (d) is used. As shown in the phase diagram, as the mixing ratio of tin from pure lead increases, the melting point gradually decreases and the wettability improves, while the eutectic point (A) (P
b: Sn = 37.3: 62.7), it is known that when the lead mixing ratio is increased and the solidus and liquidus temperatures are increased, the melting temperature increases and a high heat resistant high temperature solder material is obtained. Also, mix a predetermined amount of low-temperature solder powder with the eutectic solder powder,
A cream solder (Japanese Patent Laid-Open No. 61-129297) that has a bonding strength equivalent to that of a eutectic solder material and realizes a low melting point is known, but it is merely a reduction in the melting point of the eutectic solder material.
It does not realize high heat resistance.

[0004]

The problem to be solved is to increase the blending ratio of lead (Pb) in order to improve the heat resistance after reflow, and the viscosity does not easily drop when the solder material melts. As shown in FIG. 2 (c), the wettability of the solder material (2) becomes poor, the solderability deteriorates, and the joint strength largely decreases.

[0005]

According to the present invention, a first heat-resistant first solder material having a higher melting point is provided as an inner layer on the outer surface of a member to be joined in substantially equal amounts of first and second solder materials having different melting points. ,and,
Reflow after a step of stacking a second solder material having a lower melting point and having good wettability as an outer layer and doubly covering, and temporarily fixing the member to be joined by bringing the second solder material coated surface into contact with the joint surface. And the step of melting the second solder material by low temperature heating by, and after the second solder material is melted, the first solder material is melted by high temperature heating by reflow and the first and second solder materials are mixed to form a joined member. And a step of joining.

[0006]

According to the above technical means, the outer surfaces of the members to be joined are sequentially covered by the first and second solder materials having different melting points in substantially equal amounts.
After being laminated and double-coated, when temporarily fixed to the joint surface and heated by reflow, the second solder material having a lower melting point first melts with good wettability. Therefore, when the temperature is further increased, the high heat-resistant first solder material having a higher melting point is melted, and the second solder material of the outer layer, which has been melted earlier, becomes priming water and becomes the first solder material of the inner layer. Easily mix and achieve good wettability and high heat resistance solder material at the same time.

[0007]

Embodiment An embodiment of a joining method according to the present invention is shown in FIG.
This will be described below with reference to (b) and (c). In the figure, (1) and (3) are the members to be joined and the joining surface, respectively, as in the prior art, (4) is the first solder material, and (5) is the second solder material.
The first and second solder materials (4) and (5) are alloys or single metals having different melting points by changing the compounding ratios of tin and lead, and the first solder material (4) contains a large amount of lead. Then, for example, lead 100
% (Single substance) has a higher melting point and high heat resistance. On the other hand, the second solder material (5) is a mixture of tin and lead, such as Pb: Sn.
= 6: 4 as a eutectic alloy with a mixing ratio, lower melting point and good wettability.

The operation (method) of the present invention based on the above configuration will be described below. First, the outer surface of the member to be joined (1) is coated with the first solder material (4), and then the coated surface is coated with the second solder material (5) having a low melting point in an amount substantially equal to that of the first solder material (4). Laminate and coat double. Next, after the second solder material-coated surface is brought into contact with the bonding surface (3) to temporarily fix the bonded member (1),
When the second solder material (5) is melted by low temperature heating by reflow, the second solder material (5) in the outer layer is melted with good wettability. Then, after the second solder material (5) is melted, the first solder material (4) is melted by high-temperature heating by reflow, and the second solder material (5) of the outer layer that has been melted earlier becomes priming water and the inner layer Easily mixes with the first solder material (4), and the bonded member (1) is bonded to the bonding surface (3) with good wettability and high heat resistance at the same time.

The present invention is not limited to the above embodiment, but the first,
By changing the compounding ratio of tin and lead of the second solder material (4) and (5), each melting point can be selectively set to a desired temperature, and instead of the solder material, for example, silver is mixed with wax. A brazing material may be used.

[0010]

According to the present invention, when the members to be joined are joined by the solder material or the brazing material by reflow, the outer surfaces of the members to be joined are approximately equal in amount by the first and second solder materials having different melting points. ,
Highly heat-resistant first solder material having a higher melting point is laminated as an inner layer, and second solder material having a lower melting point and having good wettability is laminated as an outer layer and double coated, and then the second and first solders are subjected to reflow heating. Since the materials are sequentially melted and the first and second solder materials are mixed together to bond the members to be bonded, good wettability and high heat resistance can be realized at the same time.

[Brief description of drawings]

1A, 1B, and 1C are process diagrams showing an embodiment of a joining method according to the present invention.

2A and 2B are process diagrams showing an example of a conventional joining method. (C) is an explanatory view of a conventional problem.
(D) is a state diagram of a tin-lead solder material.

[Explanation of symbols]

 1 Member to be bonded 3 Bonding surface 4 First solder material 5 Second solder material

Claims (3)

[Claims] 1. A highly heat-resistant first solder material having a higher melting point as an inner layer and a lower melting point wetted surface of the members to be joined with substantially equal amounts of first and second solder materials having different melting points. A second solder material having good properties as an outer layer to be double-coated, and the second solder material-coated surface is brought into contact with the joint surface to temporarily fix the member to be joined, and then the second solder material is subjected to low temperature heating by reflow to 2 a step of melting the solder material, and after melting the second solder material, the first solder material is melted by high temperature heating by reflow,
And a step of joining the members to be joined together by mixing the solder materials. 2. The first solder material is lead, and the second solder material is a eutectic alloy of lead and tin, or both solder materials are lead and tin alloys having different mixing ratios. 1. The joining method according to 1. 3. The joining method according to claim 1, wherein a brazing material is used instead of the solder material.