JPH0518676B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to, for example, power transistors, power ICs, etc. (package components coated with molded resin, or without a cover to increase packaging density). (including bare chip parts)
heat-generating electronic components for electric power (hereinafter in this specification,
The present invention relates to a grooved sheet-shaped solder that has good thermal conductivity and is durable when attaching heat-generating electronic components (simply referred to as heat-generating electronic components) to a heat sink, and a method for manufacturing the same.

In addition, in this specification, "uncured state" means
A state in which the solvent remains without being blown off by natural drying or hot air drying, that is, a state in which the flux is not completely cured.

[Conventional technology]

A conventional example in which a heat-generating electronic component is attached to a heat sink will be described with reference to FIGS. 7 and 8. 7th
Figures A to C are explanatory diagrams for installing heat-generating electronic components in a conventional example.

As shown in FIG. 7A, the heat generating electronic component 41 is
Cream solder 4 printed on heat sink 42
3 and then passed through a reflow oven,
As shown in FIG. 7B, the cream solder 43 is
After being melted, it solidifies (see FIG. 7B, 43'), and mechanically and thermally joins the heat-generating electronic component 41 and the heat sink 42. The cream solder 43 contains about 10% by weight and about 50% by volume of flux, such as pine resin, activator, solvent, etc.

Furthermore, FIGS. 8A and 8B are explanatory diagrams for installing heat-generating electronic components in another conventional example.

As shown in FIG. 8A, a solder pellet 46 of a predetermined size, coated with flux 47 in advance, is sandwiched between the heat-generating electronic component 41 and the heat sink plate 42.
A reflow process is performed to mechanically and thermally bond the two.

[Problem to be solved by the invention]

However, cream solder 4 as shown in FIG.
3, as mentioned above, the cream solder 43 contains a lot of flux, so during reflow heating, air and flux are drawn into the solder layer as shown in FIG. Holes 44 and flux residues 45 such as pine tar are included in the cream solder 43'.

Therefore, the holes 44 and the flux residue 45 prevent the heat generated from the heat generating electronic component 41 from being transmitted to the heat sink plate 42.

In addition, the void 44 is provided in the cream solder 43.
and flux residue 45 is contained,
Repeated expansion and contraction caused by the heat cycle of heat-generating electronic components causes the solder to deteriorate and cause installation failures.

Furthermore, since the cream solder 43 is applied by screen printing, irregularities occur on the surface of the cream solder, as shown in FIG. 9A. Therefore, it is difficult to control the thickness of the cream solder 43 to be thin, so the cream solder 43 must be applied thickly, thereby eliminating the voids 44 and flux residue 45, which are the aforementioned drawbacks. A lot of it gets into the solder.

As shown in FIG. 8, when using solder pellets 46, there is an advantage that heat conduction is good because the solder is thin. However, flux must be applied to the surface of the solder pellet 46 before installation. Therefore, not only is it time-consuming to apply the flux, but also the solder wettability deteriorates unless the flux is applied uniformly.

In order to solve the above-mentioned problems, an object of the present invention is to provide a grooved sheet-shaped solder having gas exhaust grooves with good heat conduction and durability, and a method for manufacturing the same.

[Means to solve the problem]

In order to solve the above problems, the grooved sheet solder of the present invention has a plurality of grooves extending from one end surface to the other end surface of the solder alloy layer on at least one surface of the solder alloy layer rolled into a sheet shape. Continuous gas exhaust groove and the gas exhaust groove 3
2, and an uncured flux layer formed on the surface of the protrusion.

Further, it is configured to form an uncured flux layer on the inner surface of the gas exhaust groove.

The method for manufacturing the grooved sheet solder of the present invention includes:
a first step of rolling a solder ingot to form a sheet-like solder alloy layer; a flux medium;
a second step of mixing a solvent and an activator to produce a flux with predetermined characteristics; a third step of applying the flux produced in the second step to the sheet-shaped solder formed in the first step; a fourth step of drying the flux applied in the third step to an uncured state; and one end surface of the sheet-like solder on at least one surface of the sheet-like solder having the unhardened flux layer obtained in the fourth step. a fifth step of forming a plurality of continuous gas exhaust grooves reaching from one end surface to the other end surface; and reeling the sheet-shaped solder with gas exhaust grooves on which the flux layer in an uncured state obtained in the fifth step is formed. and a sixth step of winding the wire.

Further, another method for producing a grooved sheet-like solder according to the present invention includes a first step of rolling a solder ingot to form a sheet-like solder alloy layer, and at least one step of rolling a solder ingot to form a sheet-like solder alloy layer. The second step is to form a plurality of continuous gas exhaust grooves on one surface of the solder sheet, reaching from one end surface to the other end surface, and the second step is to mix a flux medium, a solvent, and an activator to produce a flux with predetermined characteristics. a fourth step of spraying the flux generated in the third step onto the sheet-like solder in which gas exhaust grooves have been formed in the second step; and a fourth step of spraying the flux sprayed in the fourth step in an uncured state. and a sixth step of winding the solder sheet with grooves for gas discharge, on which the uncured flux layer obtained in the fifth step is formed, onto a reel.

[Effect]

An uncured flux layer is previously formed on the protrusions or recesses formed in the grooved sheet-like solder. Then, the grooved sheet-shaped solder is attached so as to be sandwiched between the heat sink and the heat-generating electronic component.

Thereafter, when a reflow process is performed, the heat sink and the heat generating electronic component are bonded. During the above reflow process, the gas and flux discharged from the flux immediately before the solder melts are discharged from the gas discharge groove toward the end surface of the sheet-like solder, so there is no empty space in the molten solder. Free from pore and flux residues.

Furthermore, since there are no voids or flux residue in the solder, thermal resistance is low and heat dissipation is good.

Furthermore, since the air in the holes does not repeatedly expand and contract due to the heat cycle caused by the heat generated by the heat-generating electronic components, poor solder attachment due to aging does not occur.

[Example] An example of the present invention will be described with reference to FIGS. 1 to 5.

FIG. 1 is an explanatory diagram of the sheet-shaped solder manufacturing process in the present invention, and FIG. 3 is an explanatory diagram of the grooved sheet-shaped solder in the present invention.

In FIGS. 1 and 3, in the first step,
A solder ingot 1 is rolled 2 to form a sheet-like solder alloy layer 31. The thickness of the solder alloy layer 31 formed in a sheet shape is determined by the type of solder, the usage conditions of the solder, and the like.

For example, in this example, it is rolled to a thickness of 0.2 mm.

In the second step, a flux medium 3 mainly composed of rosin and its derivatives or imidazole derivatives, water, petroleum paste, polyethylene glycol, organic solvent, etc., which improves the applicability and workability to the joint surface, are used. or alcohol-based, solvent 4, and flux medium 3
A flux 6 having predetermined characteristics is produced by mixing with an activator 5 that improves the effect of the flux.

In the third step, the flux 6 obtained in the second step is applied to both surfaces of the sheet-shaped solder alloy layer 31 rolled 2 in the first step to form flux layers 33 and 34. The application of flux 6 is
Repeat multiple times if necessary to obtain the desired thickness.

Further, by applying the flux a plurality of times, not only can pinholes in the flux 6 be eliminated, but also the characteristics of the flux layer can be adjusted by alternately applying fluxes 6 having different characteristics.

In the fourth step, the flux 6 applied in the third step is air-dried or dried with hot air to bring it into an uncured state in which the solvent remains. If the flux 6 is dried in an inert atmosphere such as _N2 , the drying time will be shortened.

In the fifth step, the flux 33 in an uncured state,
One end surface 3 of sheet-like solder on which 34 is formed
5 to the other end surface (not shown) are formed. The gas exhaust groove 32 has a groove depth of 0.1 mm and a groove width of 0.3 mm, for example. Furthermore, the means for forming the gas discharge groove 32 includes, for example, knurling, cutting with a cutter, embossing with a press, and the like. The processing method can be appropriately selected depending on the thickness of the solder sheet, the shape and dimensions of the groove to be formed, the properties of the flux layer, etc.

In the sixth step, the grooved sheet solder 30 having the gas exhaust grooves 32 and uncured flux layers 33 and 34 obtained in the fifth step is wound around a reel. If the adhesiveness of the flux layers 33 and 34 is strong, the grooved sheet solder 3 is removed in the sixth step.
When winding 0 onto a reel, a film (not shown) can be wound between the grooved sheet solder 30.

Further, other embodiments of the present invention are shown in FIGS. 2 to 4.
This will be explained with reference to the figures. FIG. 2 is an explanatory diagram of another sheet-shaped solder manufacturing process according to the present invention, and FIG. 4 is a sectional view of the grooved sheet-shaped solder.

In FIGS. 2 and 4, the difference from the embodiment described above is that the order of the steps is different.

That is, in the first step, only a sheet-like solder alloy layer 31 is formed. In the second step, gas exhaust grooves 32 similar to those in the previous embodiment are formed on at least one surface of the sheet-shaped solder alloy layer 31. Third
Flux 6 is also generated in the process. Fourth
In the step, the flux 6 is sprayed onto both sides of the grooved sheet-shaped solder 30 to form flux layers 34 and 36 including the inside of the gas exhaust grooves 32. In the fifth step, the flux layer 34,
36 is dried to an uncured state with the solvent remaining. In the sixth step, the flux layer 3 in an uncured state is
A grooved sheet-like solder 30 having numbers 4 and 36 formed thereon is wound onto a reel (not shown). Depending on the viscosity of the flux layers 34 and 36, a film can be wound between the grooved solder sheets 30.

Next, while referring to the explanatory diagram for installing heat generating electronic components shown in FIG.
This section explains how to install the .

First, the grooved sheet solder 30 is placed on the heat sink 37.
and the heat-generating electronic component 38. In this state, it is placed in a reflow oven (not shown). Flux layers 33, 34, 3 formed in an uncured state on the grooved sheet-like solder 30
6 becomes gaseous and acts as a flux, and is no longer needed and is discharged from the gas discharge groove 32. At the same time, the grooved sheet solder 3
0 is melted and heat sink 37 and heat generating electronic component 3
8 are joined. After that, the flux scattered around the heat sink 37 and the heat generating electronic components 38 is
Washed.

As a result of experiments using the solder sheet 30 with gas discharge grooves and the solder pellets without gas discharge grooves under the same conditions, it was found that the solder sheet 30 with grooves for gas discharge has holes 44 and flux. The number of residues 45 was small, and the variation in distribution was also small.

Furthermore, in order to confirm the gas evacuation effect of the gas evacuation grooves 32, the one shown in FIG. 5 was changed from a horizontal state to a vertical state during reflow. As a result, the voids 44 and flux residue 45 in the solder decreased as the gas exhaust grooves 32 of the solder sheet with gas exhaust grooves oriented vertically upward.

FIGS. 6A to 6D show other embodiments of the gas exhaust groove according to the present invention.

Figure 6a shows the gas exhaust groove 32 connected to the solder alloy layer 3.
This is an example in which they are provided on the front surface 51 and back surface 52 of 1.

Further, FIG. 6B shows an example in which the gas exhaust grooves 32 are provided so as to intersect with each other, FIG. 6C shows an example in which the gas exhaust grooves 32 are provided in an inclined manner, and FIG. FIG. 6E shows an example in which the gas exhaust grooves 32 are provided in a zigzag pattern.
Furthermore, although the cross section of each groove is shown to be rectangular, it can be arbitrarily modified to a triangular groove as shown in FIG. 6 or a semicircular groove as shown in FIG.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. Various design changes can be made without departing from the scope of the invention as set forth in the claims.

For example, the shape, width, and depth of the gas exhaust groove vary depending on the area of the part to be soldered, the thickness of the solder to obtain the desired attachment strength, etc., and can be changed arbitrarily. It is also possible to combine shaped gas exhaust grooves.

Furthermore, in this example, a case was explained in which a sheet-shaped solder was used when attaching a heat-generating electronic component to a heat sink, but the sheet-shaped solder of the present invention can be applied to soldering other electronic components or mechanical components. Needless to say.

[Effects of the Invention] According to the present invention, since the flux is previously formed in an uncured state in the protrusions or recesses of the grooves formed in the grooved sheet-like solder, the flux melts into the sheet immediately before the solder melts. The solvent and unnecessary flux can be turned into a gas and discharged to the outside from the gas discharge groove of the shaped solder. Therefore, since no air or flux residue remains in the solder, thermal resistance due to pores and flux residue is reduced and heat dissipation is improved. Furthermore, since there are few pores, there is no stress caused by repeated expansion and contraction due to heat generated by heat-generating electronic components, and the solder does not deteriorate even with aging.

Further, according to the present invention, since the flux applied to the sheet-like solder has a suitable viscosity in an uncured state, the mounting position of the heat sink or the heat-generating electronic component does not shift during assembly.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the sheet-shaped solder manufacturing process according to the present invention, FIG. 2 is an explanatory diagram of another sheet-shaped solder manufacturing process according to the present invention, FIG. 3 is an explanatory diagram of the sheet-shaped solder with grooves according to the present invention, and FIG. 5 is a cross-sectional view of the sheet-like solder with grooves, FIG. 5 is an explanatory diagram for installing heat-generating electronic components, FIGS. FIGS. 8A and 8B are explanatory views of installing a heat generating electronic component in another conventional example, and FIGS. 9A and 9B are explanatory views comparing cream solder and solder pellets. 30... Grooved sheet solder, 31... Solder alloy layer, 32... Gas exhaust groove, 33... Flux layer, 34... Flux layer, 35... End surface, 36... Flux layer, 37... Heat sink, 3
8...Heat-generating electronic components.

Claims (1)

[Claims] 1. Solder alloy layer 31 rolled into a sheet shape
on at least one surface of the solder alloy layer 31, a plurality of continuous gas exhaust grooves 32 reaching from one end surface 35 to the other end surface, a protrusion adjacent to the gas exhaust groove 32, and a protrusion formed on the surface of the protrusion. A grooved sheet-like solder comprising: flux layers 33, 34 in an uncured state. 2. The grooved sheet solder according to claim 1, further comprising an uncured flux layer formed on the inner surface of the gas exhaust groove. 3. A first step of rolling a solder ingot to form a solder alloy layer 31 into a sheet shape; a second step of mixing a flux medium 3, a solvent 4, and an activator 5 to produce a flux with predetermined characteristics; a third step of applying the flux produced in the second step to the sheet-shaped solder formed in the first step; a fourth step of drying the flux applied in the third step to an uncured state; a fifth step of forming a plurality of continuous gas exhaust grooves reaching from one end surface of the sheet-like solder to the other end surface on at least one surface of the sheet-like solder having the uncured flux layer obtained in the fourth step; a sixth step of winding the grooved sheet solder for gas discharge, on which the flux layer is formed in an uncured state obtained in the fifth step, around a reel; Production method. 4. A first step of rolling a solder ingot to form a sheet, and a plurality of continuous gas discharges reaching at least one side of the solder sheet obtained in the first step from one end surface of the solder sheet to the other end surface. a second step of forming a gas discharge groove; a third step of mixing a flux medium 3, a solvent 4, and an activator 5 to produce a flux having predetermined characteristics; and a gas discharge groove formed in the second step. a fourth step of spraying the flux generated in the third step onto the sheet-shaped solder; a fifth step of drying the flux sprayed in the fourth step to an uncured state; and uncured flux obtained in the fifth step. a sixth step of winding the grooved sheet solder for gas discharge, on which the flux layer is formed, around a reel;