JPH03254392A - Sheet-like solder and its production - Google Patents

Abstract

PURPOSE:To improve the quality of joining solder by using sheet-like solder obtained by forming a flux layer being in an unhardened state on an alloy layer rolled like a sheet. CONSTITUTION:Sheet-like solder 11 is constituted of a solder alloy layer 12 rolled like a sheet, and a flux being in an unhardened state formed thereon. In such a way, since the flux does not go into the sheet-like solder 11, a pore and a residue do not exist in joined solder and its quality can be improved. It is utilized effectively for manufacturing grooved sheet-like solder with high thermal conductivity and high durability at the time of attaching power heating electronic parts such as a power transistor and a power IC, etc., to a cooling body.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to, for example, power transistors, power ICs, etc. (packaged components covered with molded resin, or not covered in order to increase packaging density). A durable grooved sheet with good thermal conductivity is used when attaching heat-generating electronic components (hereinafter simply referred to as heat-generating electronic components in this specification) for power use (including T-chip components) to a heat sink. The present invention relates to a shaped solder and a method for manufacturing the same.

In this specification, the term "uncured state" refers to 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. 3 and 4. FIGS. 3(A) to 3(C) are explanatory diagrams of the mounting of heat-generating electronic components in the conventional example.

As shown in FIG. 3(a), the heat generating electronic component 21 is placed on the cream solder 23 printed on the heat sink 22, and then passed through a reflow oven. As shown, the cream solder 23 solidifies after melting (
(See FIG. 3(b) 23'), and the heat-generating electronic component 21 and the heat sink plate 22 are mechanically and thermally bonded. Note that the cream solder 23 contains flux of about 10% by weight and about 50% by volume, such as pine tar,
Contains activators, solvents, etc.

Further, FIGS. 4(a) and 4(b) are explanatory diagrams of the mounting of heat-generating electronic components in other conventional examples.

As shown in FIG. 4(a), solder pellets 26 of a predetermined size, coated with flux 27 in advance, are sandwiched between the heat-generating electronic component 21 and the heat sink 22, and a reflow process is performed to mechanically and Thermal bonding.

[Problem to be solved by the invention]

However, when using the ream solder 23 as shown in FIG. 3, the cream solder 23 contains a large amount of 7 lux as described above, so that during reflow heating, as shown in FIG.
c) As shown in the figure, air and flux are caught in the solder layer, and after solidification, there are voids 24 and flux residues 25 such as pine resin in the cream solder 23'.
Therefore, the pores 24 and the flux residue 25 prevent the heat generated from the heat-generating electronic component 21 from being transmitted to the heat sink plate 22 .

Furthermore, if the voids 24 and flux residue 25 are present in the cream solder 23, the repeated expansion and contraction caused by the heat cycle of the heat-generating electronic components will cause the solder to deteriorate and cause installation failure. becomes.

Furthermore, since the cream solder 23 is applied by screen printing, irregularities occur on the surface of the cream solder as shown in FIG. 5(A). Therefore, it is difficult to manage the thickness of the cream solder 23 thinly.
Since the cream solder 23 must be applied thickly, the voids 24 and flux residues 25, which are the disadvantages mentioned above, often penetrate into the solder.

As shown in FIG. 4, when using solder pellets 26, there is an advantage that the solder can be made thinner to improve heat conduction, or that voids 24 and flux residues do not enter the solder.

However, before attaching the heat sink and the heat-generating electronic components, flux 27 must be applied to the surface of the solder pellets 26 in advance. 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, the present invention aims to provide a sheet-shaped solder having an uncured flux layer and a method for manufacturing the same.

[Means to solve the problem]

In order to achieve the above objects, the sheet solder of the present invention includes a solder alloy layer rolled into a sheet,
and an unhardened flux layer formed on the solder alloy layer.

Further, the sheet-shaped solder of the present invention is configured to be wound around a reel by winding a film between the sheet-shaped solder.

The method for producing a sheet-like solder of the present invention includes a first step in which a solder ingot is rolled to form a solder alloy layer into a sheet-like shape.
a second step of mixing a flux medium, a solvent, and an activator to produce a flux with predetermined characteristics; and applying the flux produced in the second step to the sheet-shaped solder alloy layer rolled in the first step. A third step of applying
a fourth step of drying the flux applied in the third step to an uncured state; and a fifth step of winding the sheet-like solder on which the uncured flux layer obtained in the fourth step is formed around a reel. It consists of a process.

[For production]

The solder ingot is rolled to a thickness suitable for joining the heat-generating electronic component and the heat sink. Then, a flux mixed with a solvent and an activator so as to have the required properties is applied to the rolled sheet-like solder alloy layer.

In this state, the flux is dried by natural drying or hot air drying so that the solvent remains uncured.

Since the flux layer formed on the solder sheet is in an uncured state, it will not fall off as dust during work. Such sheet-shaped solder is wound onto a reel and shipped as solder for heat-generating electronic components. Further, depending on the dry state of the flux layer, it is also possible to wind the flux layer around a reel while winding a film between sheets of solder if necessary.

Flux is applied to the solder sheet in advance, which not only simplifies the process of attaching heat-generating electronic components to heat sinks, such as solder pellets, but also makes it easier to attach heat-generating electronic components, such as solder pellets, to heat sinks.Since the solder does not contain flux, it does not need to be emptied during reflow processing. No holes or flux residue mixed into the solder.

Therefore, the heat generated by the heat generating electronic component is efficiently transmitted to the heat sink, and the solder does not deteriorate even if a heat cycle occurs due to the heat generating electronic component.

〔Example〕

An embodiment of the present invention will be described with reference to FIG. 1st
The figure is an explanatory diagram of the sheet-shaped solder manufacturing process in the present invention.

In the first step, a solder ingot 1 is rolled 2 to form a solder alloy layer into a sheet shape. The thickness of the solder alloy layer formed in a sheet shape is determined by the type of solder, the conditions under which the solder is used, and the like.

In the second step, a flux medium 3 mainly composed of, for example, rosin and its derivatives, or an imidazole derivative, and water, petroleum-based paste, polyethylene glycol,
An organic or alcoholic solvent 4 and an activator 5 that improves the effectiveness of the flux medium 3 are mixed to produce a flux 6 with predetermined characteristics.

In the bs3 step, the flux 6 produced in the second step is applied to at least one surface of the sheet-shaped solder alloy layer rolled 2 in the first step. Applying flux 6 is
Repeat multiple times if necessary to obtain the desired thickness. Also,
Applying the flux multiple times not only makes it possible to eliminate pinholes in the flux 6, but also makes it possible to adjust the properties of the flux layer by alternately applying fluxes 6 with different properties.

In the fourth step, the flux 6 applied in the third step is air-dried or dried with hot air to leave it uncured and with the solvent remaining. When drying flux 6, use N2
The drying time will be shortened if it is carried out in an inert atmosphere such as

In the fifth step, the sheet-like solder having the flux layer obtained in the fourth step is wound around a reel.

Since the flux 6 has adhesive properties due to its properties, a film can be wound between the solder sheets when the solder sheets are wound around a reel in the fifth step.

A sheet-shaped solder manufactured by the above process is shown in FIG. 2.

FIG. 2(A) is a schematic diagram of a sheet-shaped solder, and FIG. 2(B) is an external view of the sheet-shaped solder according to the present invention wound on a reel.

In the sheet-like solder 11, a flux layer 13 is formed on at least one surface of a rolled solder alloy layer 12.

This sheet-like solder 11 is wound around a reel 14 as shown in FIG. 2(b). In addition, in FIG. 2(b), the film wound between the sheet-like solder 11 is omitted.

The sheet-shaped solder 11 is cut into an appropriate size and then placed between the heat-generating electronic component 21 and the heat sink 22,
The above-mentioned two are joined by passing through a reflow oven.

Further, since no flux is contained inside the sheet-like solder 11, voids 24 and flux residues 25 are not contained in the solder layer at the joint portion. Therefore, even if a heat cycle is applied to the heat generating electronic component 21, the thermal conductivity and bonding strength are not affected.

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 degree to which flux is dried to an uncured state differs depending on whether sheet solder is used manually or in an automated machine, and also depends on the size of heat-generating electronic components or the size of other electronic components. Since it varies depending on the temperature of the solder to be attached, etc., it can be changed arbitrarily as necessary.

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.

〔Effect of the invention〕

According to the present invention, since the flux does not enter the solder sheet and is formed on the surface of the solder in an uncured state, there are no voids and no flux residue in the solder that is bonded.

Therefore, the heat generated by the heat generating electronic component is efficiently conducted to the heat sink, and the bonding strength is not affected by the heat cycle of the heat generating electronic component.

Further, according to the present invention, since the flux applied to the sheet-like solder alloy layer has an appropriate viscosity in an uncured state, the attachment position does not shift when the heat sink and the heat-generating electronic component are assembled.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the sheet-shaped solder manufacturing process in the present invention, Figures 2 (a) and (b) are explanatory diagrams of the sheet-shaped solder in the present invention, and Figures 3 (a) to 3) are heat generation in the conventional example. The electronic component installation is an explanatory diagram. Figures 4 (a) and (b) are explanatory diagrams of the heat-generating electronic component installation in other conventional examples. Figure 5 (a) and the opening are diagrams showing cream solder and solder pellet FIG. 11... Sheet-shaped solder 12... Solder alloy layer 13... Flux layer 14... Reel No. 111 (a) (b) Explanatory diagram of sheet-shaped solder in this investigation! 211 (A) (0) (C) The explanatory drawing section 31 shows the installation of heat-generating electronic components in the conventional example! 22 Heat dissipation plate / (a) 21 Thermal electronic components (b) Figure (a) (b) Comparison diagram of cream solder and solder pellet I.

Claims (3)

[Claims] (1) A sheet-like solder comprising: a solder alloy layer 12 rolled into a sheet-like shape; and an unhardened flux layer 13 formed on the solder alloy layer 12. (2) Claim (2) characterized in that a film is wound between the sheet-like solder 11 and wound around a reel.
1) The long sheet-shaped solder described above. (3) A first step of rolling a solder ingot 1 to form a sheet-like solder alloy layer 12, and a second step of mixing a flux medium 3, a solvent 4, and an activator 5 to produce a flux with predetermined characteristics. and a sheet-shaped solder alloy layer 1 rolled in the first step.
a third step of applying the flux 6 produced in the second step to the second step; a fourth step of drying the flux 6 applied in the third step to an uncured state; The flux layer 13 in the state
A method for manufacturing sheet solder, comprising: a fifth step of winding sheet solder 11 having a formed thereon around a reel.