JP2816084B2 - Solder coating method, semiconductor device manufacturing method, and squeegee - Google Patents

Abstract

PURPOSE:To enable uniform solder coating with a metal mask having step- difference, by pressing and sliding a squeegee two-step-wise. CONSTITUTION:When solder 33 is printed via a second through hole 17 of a second mask plate 15 wich is stepped to a first mask plate 12, firstly solder is buried in the first through hole 14 by using a first squeegee 30, and secondly superfluous solder 33 on the second mask plate 15 is eliminated by using a second squeegee 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for applying a solder which can apply a cream solder uniformly over a large area and a method for manufacturing a semiconductor device using the same.

[0002]

2. Description of the Related Art Video packs (product names) in which video output circuits such as TVs and HDTVs are integrated with discrete components.
Has been commercialized by the present applicant (for example, Japanese Patent Application Laid-Open No. 4-112560). Since such devices require high frequency and high output, a low dielectric constant ceramic substrate is used as the circuit board, each chip element and circuit conductor are formed on this surface, and the whole is hermetically sealed with an aluminum die-cast housing. The technique of doing is adopted.

[0003] However, since the aluminum die-cast housing is expensive, attempts have been made to seal it with a resin mold instead of the housing. Moreover, in order to simplify the assembly line and share the technology with the IC assembly technology,
It has been considered to use what is on the extension of a lead frame with a heat sink for a so-called power IC. FIG. 6 shows the configuration in this case. A lead frame including a first member including a frame (2) including a plurality of leads (1);
A second heat sink (3) having a thickness greater than that of the lead (1);
Are manufactured separately, and the second member composed of the heat sink (3) is integrated with the first member by caulking at four mounting portions (4). Since the tip of the lead (1) extends on the metal heat radiating plate (3), a gap of about 0.5 mm is provided between the two to maintain electrical insulation. Then, a ceramic substrate (5), on which active and passive elements, circuit conductors for connecting these elements and pads for external connection are formed in advance, is fixed on a heat sink (3), and the pads, leads (1) and Is wire-bonded with a gold wire (6), and the main part up to a position near the dashed-dotted line (7) is sealed with a thermosetting resin (8).

Such a configuration differs from the conventional hybrid integrated circuit in that the external leads are not leads with clip terminals or the like which are individually soldered but lead (1) of a lead frame. Further, the configuration is different from the conventional power IC in that a large ceramic substrate (5) is fixed on the heat radiating plate (3) instead of the silicon chip. for that reason,
A new problem occurs that cannot be solved by the conventional IC assembly technology.

[0005] One of the new problems is the adhesion of the ceramic substrate (5). The transistor chip is already die-bonded to the surface of the ceramic substrate (5), and the bonding between the heat sink (3) and the ceramic substrate (5) must be performed at a temperature that does not adversely affect the chip (about 400 ° C. or less). No. The ceramic substrate (5) is 14 × 23 m
Since the material has a large area of m and is easily broken by strain, it is necessary to use an adhesive which has a small strain and can be uniformly applied to a large area. Therefore, it has been studied to apply a high melting point cream solder using a metal mask as an adhesive. The metal mask is a single thin plate having a through-hole. The through-hole of the metal mask is overlapped on the heat sink (3), and the squeegee is pressed and slid to remove the cream solder supplied onto the metal mask. This is to be imprinted on the surface of the heat sink (3) through the through hole. This technique is frequently used in hybrid integrated circuits.

[0006]

However, the above-described device differs from the hybrid integrated circuit in that a lead frame is used as described above. Therefore, heat sink (3)
There is a disadvantage that the metal mask cannot be brought into close contact with the step due to the step between the metal mask and the lead (1), and a slight gap is formed between the metal mask and the heat radiating plate (3). If a gap is formed, it becomes impossible to apply the cream solder evenly, which hinders later steps.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional drawbacks, and has as its object to provide a method which can uniformly apply even a step having a step such as a lead frame. A first squeegee (30) that slides on the first mask plate (12) while using a metal mask composed of first and second mask plates (12) and (15) with steps; The main point is that the solder is applied in two stages with the second squeegee (31) sliding on the second mask plate (15).

[0008]

According to the present invention, the first and second mask plates (3)
0) and (31), the lead (2)
The second mask plate (15) can be brought into close contact with the heat radiating plate (22) while avoiding the step (0). At the same time, a flat first squeegee (30) is first pressed and slid on a metal mask having a step, thereby forming a first through hole (14).
The inside is buried with the solder (33), and then the excess solder (3) in the first through hole (14) is formed by the second comb-shaped squeegee (31).
Since 3) is removed, solder (33) printed through the second through hole (17) and solder (30) on the metal mask are removed.
Can be reliably separated. In addition, an accurate and stable amount of the solder (33) can be uniformly applied.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. First, referring to FIGS. 2 to 4, a metal mask used in the manufacturing method of the present invention has a thickness of 0.1 to 0.3 on a frame body (11) made of an aluminum alloy having a square rod shape as a whole.
1 mm mask plate made of stainless steel (12)
Are fixed by welding, and through holes (13) of the same size are provided at regular intervals near the center of the first mask plate (12).

FIGS. 3 and 4 show enlarged portions of the through hole (13). 3 and 4, the first mask plate (1
2) is provided with a first through-hole (14) having a size of 7.0 × 25.0 mm, and has a thickness of 0.2 to 0.2 mm so as to close the first through-hole (14). A second mask plate (15) made of a 3 mm stainless steel alloy has an annular spacer (1).
It is attached by spot welding via 6). The first mask plate (12) and the second mask plate (15) are fixed so that their horizontal surfaces are parallel to each other, and the step between the two by the spacer (16) is 0.8 to 1.0 mm. A second through hole (17) having a size of 3.0 × 25.0 mm is provided at substantially the center of the second mask plate (15), and the second through hole (17) is used for applying solder. Mask pattern. The outer circumference of the spacer (16) is 11.0 × 29.0 mm.

The relationship between the lead frame and the metal mask in the assembling process is as follows. Referring to FIG. 5, the lead frame is formed together with the lead (20) from a single plate-like material by punching or etching. It has a first member composed of a frame (21) and a second member composed of a radiator plate (22) formed of a plate-like material thicker than the leads (20), and has four mounting portions (23). ), The first member and the second member are integrated so that the heat radiating plate (22) and the lead (20) have a step. When the frame (21) is aligned with such a lead frame having a uniform height as a whole and a metal mask is overlaid, the back surface of the second mask plate (15) is placed on the surface of the heat radiating plate (22). In contact, as shown in FIG. 6, the first mask plate (15) is located above the lead (20) due to the step formed by the spacer (16). Of course, the first
The height difference between the mask plate (12) and the second mask plate (15) is larger than the height difference between the heat radiating plate (22) and the lead (20), and the spacer (16) when aligned.
The thickness and size of the second mask plate (15) are designed so that the second mask plate (15) does not overlap the lead (20) or the frame (21) other than the lead (20). (24) is a work table. With such a design, any position of the first mask plate (12) does not come into contact with the frame (21) of the lead frame, so that the second mask plate (15) is connected to the heat radiating plate (22).
Can be evenly brought into contact with the surface.

FIGS. 7 and 8 show the first and second embodiments respectively used in the present invention.
FIG. The first squeegee (30)
Is made of hard rubber having a flat bottom surface with a thickness of 10 to 20 mm, and has a length that can be just fit in the frame (11) in the longitudinal direction of the metal mask. The second squeegee (31) is made of stainless steel having a plate thickness of 0.5 mm, and is similar to the first squeegee (30) in the longitudinal direction of the metal mask (1).
The first through-hole has a length just enough to fit within 1), and has a width and height corresponding to the short side and the step of the first through-hole (14) of the rutal mask. It has the same number as the number of (14). (33) is a screw hole used for clamping and fixing the squeegee body.

Then, the first and second squeegees (30)
The manufacturing method of the present application using (31) is as follows.
First, a metal mask is superimposed on the heat radiating plate (22) of the lead frame in the state shown in FIGS. 5 and 6, and cream solder is supplied onto the first mask plate (12). As shown in FIG. 1A, the cream solder (33) on the first mask plate (12) is pressed and slid on the first mask plate (12) with a first squeegee (30). Scrape off. Although the first squeegee (30) has some elasticity, the solder cream (33) in the first through hole (14) cannot be removed if the step is large. Therefore, the first squeegee (3
By sliding 0), the process is such that the solder cream (33) is embedded in the first through hole (14).

Next, as shown in FIG. 1B, this time, the convex portion (32) of the second squeegee (31) is inserted into the first through hole (14), and the convex portion (32) is inserted. The tip is brought into contact with the surface of the second mask plate (15), and the second squeegee (31) is pressed and slid in this state to thereby make the first through-hole (1).
4) Remove the excess solder cream (33) remaining inside.

After that, the metal mask is removed, so that an amount of solder cream (33) corresponding to the size of the second through hole (17) and the thickness of the second mask plate (15) is formed on the heat sink (22). Is printed. The solder cream (33) printed in this manner is completely separated from the solder cream (33) on the metal mask by sliding of the second squeegee (31). There is no difference in film thickness depending on the remainder, and the film can be applied with a uniform film thickness over the entire surface. Accordingly, the step of bonding the ceramic substrate (5) to the heat radiating plate (3) as shown in FIGS.
Since 3) is uniformly applied, the ceramic substrate (5)
Cracks and the like do not occur.

A first squeegee (30) having increased elasticity
If only the treatment is performed, as shown in FIG. 11, the solder cream (33) in the second through-hole (17) has a slightly concave shape at the center, and the supply amount is not stable. In the present application, since the horizontal portion of the convex portion (32) of the second squeegee (31) slides on the surface of the second mask plate (15), the surface of the solder cream (33) is also horizontal, and the supply amount is reduced. Stabilize.

Further, in the manufacturing method of the present invention, the distance between the second mask plate (15) and the heat radiating plate (22) to be coated is set to zero, and the metal mask main body is mechanically lifted to form the second mask plate. By removing the solder (33) from the mask plate (15), the printed pattern of the solder (33) can be finished with high precision. Generally, in printing using a metal mask, it is common to provide a space between the metal mask and the object to be coated. Then, as shown in FIG.
The squeegee (42) is pressed and slid so that the printing medium (0) comes into contact with the printing medium (41), and ink is drawn out of the mask hole by the restoring force (tension) of the mask plate (40). However, the metal mask according to the present invention includes first and second metal masks.
Because of having the mask plates (12) and (15), a high tension as in the related art cannot be obtained. Therefore, if the solder cream (33) is applied in a state where the space is provided, the solder cream (33) will flow from the second through hole (17) to the back surface of the second mask plate (15).
Therefore, in the present application, the distance between the two is set to zero to prevent the solder cream (33) from going around.

[0018]

As described above, according to the present invention, the first and second squeegees (30) and (31) perform the two-stage solder application, so that the step is formed in the first through hole (14). This has the advantage that the solder (33) can be applied uniformly even with a metal mask having the following. Then, a two-stage coating is performed with the first and second squeegees (30) and (31) using a stepped metal mask, so that the lead having a step between the heat radiating plate (22) and the lead (20). Heat sink (2
2) Solder cream can be uniformly applied on top. Therefore, there is an advantage that the large-area ceramic substrate (5) can be assembled with high yield without cracking and chipping.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining the present invention.

FIG. 2 is a perspective view showing a metal mask.

FIG. 3 is a perspective sectional view showing a main part of a metal mask.

FIG. 4 is a plan view showing a main part of the metal mask.

FIG. 5 is a plan view showing a state where a metal mask is overlaid.

FIG. 6 is a cross-sectional view showing a state where a metal mask is overlaid.

FIG. 7 is a perspective view showing a first squeegee.

FIG. 8 is a perspective view showing a second squeegee.

FIG. 9 is a plan view showing a semiconductor device.

FIG. 10 is a cross-sectional view illustrating a semiconductor device.

FIG. 11 is a cross-sectional view for explaining a solder application state.

FIG. 12 is a cross-sectional view for explaining a conventional screen printing technique.

Claims (6)

(57) [Claims] A first mask plate provided with a first through-hole, a second mask plate closing the first through-hole so as to have a step with the first mask plate, and the second mask plate; A metal mask having a second through-hole provided in the mask plate is placed on the object to be coated, and the first squeegee is slid to bury the inside of the first through-hole with solder. Metal by removing excess solder in the first through hole by sliding a squeegee 2 and applying a solder material through the second through hole on the object to be coated. Solder coating method using a mask. 2. A first mask plate provided with a first through-hole when solder is applied on a heat radiating plate of a lead frame in which a tip of a lead overlaps a heat radiating plate with a space therebetween, and the first mask is provided. A metal mask including a second mask plate that covers the first through hole so as to have a step with the plate, and a second through hole provided in the second mask plate is placed on the heat sink. In this state, the second mask plate is in contact with the surface of the heat radiating plate avoiding the leads, and slides a first squeegee to bury the inside of the first through hole with solder. An excess solder in the first through hole is removed by sliding a second squeegee, and a solder material is applied on the heat sink through the second through hole. A method for manufacturing a semiconductor device. 3. The method according to claim 1, wherein the first squeegee is made of a hard rubber. 4. The squeegee according to claim 1, wherein the second squeegee has a protrusion that matches a step between the first through hole and the second mask plate. 2. The method for applying a solder or the method for manufacturing a semiconductor device according to item 2. 5. The method for applying a solder or the method for manufacturing a semiconductor device according to claim 1, wherein the solder is applied in a state where the second mask plate and the object to be coated are in close contact with each other. 6. A squeegee having a comb-shaped protrusion.