JPH0677636A - Surface mounting method for semiconductor component - Google Patents

Abstract

PURPOSE:To provide a surface mounting method of semiconductor component in which reliability is enhanced in the connection between lead and pad. CONSTITUTION:When a semiconductor component is mounted on a circuit board by applying cream solder 10 onto pads 6 arranged on the surface of a circuit board 5 and then subjecting the pads 6 and the leads 3 of the semiconductor component to reflow soldering, a bonding tool 40 comprising a frame body 41 having stepped H end face 45 is employed after temporarily mounting a semiconductor component 1 on the circuit board 5 while aligning the seat part 3A of the lead 3 with a corresponding pad 6. Top face of the seat part 3A is then pressed by the inner stepped end face 47 of the bonding tool 40 to abut the outer peripheral stepped end face 46 on the surface of the circuit board 5 thus reflow soldering the leads 3 and the pads 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface mounting method for semiconductor parts. The leaded semiconductor component is generally surface-mounted by reflow soldering as shown in FIG.

In FIG. 3, 1 is a QFP (Quad Flated).
Package) type semiconductor components, in which substantially Z-shaped leads 3 are arranged in parallel at equal intervals on each of the four peripheral edges of the bottom surface of the package 2.

On the circuit board 5 on which the semiconductor component 1 is surface-mounted, corresponding to the leads 3 of the semiconductor component 1 at desired positions,
Pads 6 are arrayed in a frame shape. The pad 6
Is slightly wider than the width of the seat 3A of the lead 3,
It is a strip shape whose length is sufficiently larger than the length of the seating portion 3A.

The semiconductor component 1 is placed on such a circuit board 5, and the seating portions 3A of the respective leads 3 and the pads 6 are adhered to each other via the reflowed solder 10, so that the semiconductor component 1 is attached to the circuit board 5. Surface mounted.

At this time, since the shape of the pad 6 is made larger than the shape of the seat 3A as described above, the solder 10 adheres to the side surface of the seat 3A at the rear of the seat 3A and rises to the heel 11. Further, the fillet 12 is attached to the side surface of the seat 3A at the front of the seat 3A and stands up.

Therefore, as compared with the case where the lower surface of the seat 3A and the upper surface of the pad 6 are simply bonded via solder,
Strong soldering strength.

[0007]

2. Description of the Related Art A conventional surface mounting method for semiconductor parts is shown in FIG.
Shown in. In FIG. 4, reference numeral 20 denotes a bonding tool provided with a frame-shaped main body 21 having a rectangular cavity similar to the shape of the package 2 of the semiconductor component 1 in plan view and having a desired larger size in the lower portion of the central portion.

To surface mount the semiconductor component 1, first,
The cream-like solder 10A is applied by screen printing to the respective surfaces of the pads 6 arranged in a frame shape on the surface of the circuit board 5.

Next, with a robot hand (not shown), the semiconductor component 1 is sucked and transferred onto the circuit board 5, the lead 3 is aligned with the corresponding pad 6, and the seat 3A of the lead 3 is seated.
Is placed on the cream solder 10A, and the semiconductor component 1 is temporarily placed on the circuit board 5.

After that, the bonding tool 20 in which the frame-shaped main body 21 is heated to approximately 240 ° C. is lowered, and the lower end surface 22 of the frame-shaped main body 21 presses the upper surface of the seating portion 3A. The pressure applied to the seat is 10 g / mm ² .

As a result, the cream-like solder 10A is re-melted to form a solder layer having a film thickness of about 10 μm between the lower surface of the seating portion 3A and the upper surface of the pad 6, and the surface tension of the molten solder causes the solder layer 10A of FIG. Heel 11 and fillet as shown in
12, and the semiconductor component 1 is reflow-soldered on the circuit board 5.

[0012]

In the surface-mounted semiconductor component as described above, the semiconductor component and the circuit board respectively expand due to an increase in ambient temperature or heat generated by the operation of the semiconductor component.

By the way, since the coefficient of thermal expansion of the package of the semiconductor component and the coefficient of thermal expansion of the circuit board differ by about one digit,
A tensile force acts on the solder between the leads of the semiconductor component and the pads of the circuit board.

On the other hand, the thickness of the solder layer formed by the conventional method is about 10 μm as described above. Therefore, there is a problem in that the solder cannot withstand this tensile stress, a crack is generated in the solder, the lead and the pad are disconnected, or the connection becomes defective.

The present invention was created in view of the above circumstances, and an object of the present invention is to provide a surface mounting method for a semiconductor component having high reliability of connection between leads and pads.

[0016]

In order to achieve the above object, the present invention, as illustrated in FIG. 1, applies a cream solder to a pad arranged on the surface of a circuit board to lead a semiconductor component. When the semiconductor component is mounted on the circuit board by reflow soldering the pad and the pad, the seating portions 3A of the leads 3 are aligned with the corresponding pads 6, and the semiconductor component 1 is temporarily mounted on the circuit board 5. To do.

Next, a bonding tool 40 provided with a frame-shaped main body 41 having a stepped end surface 45 having a predetermined step H as the frame-shaped end surface.
The upper surface of the seating portion 3A is pressed by the inner step end surface 47 of the stepped end surface 45 of the heated bonding tool, the outer peripheral step end surface 46 of the stepped end surface 45 is brought into contact with the surface of the circuit board 5, and the lead 3 and The pads 6 are to be reflow-soldered.

Alternatively, as illustrated in FIG. 2, a frame-shaped main body 41 having a stepped end surface 45 having a predetermined step H as a frame-shaped end surface, and means for adsorbing the semiconductor component 1 inside the frame-shaped main body 41. Using the provided bonding tool 40, the semiconductor component 1 is sucked into the frame-shaped body 41 to carry the semiconductor component 1, and the seating portions 3A of the leads 3 are aligned with the corresponding pads 6.

Next, the inner step end surface 47 of the stepped end surface 45 of the heated bonding tool 40 presses the upper surface of the seating portion 3A, and the outer peripheral step end surface 46 of the stepped end surface 45 is brought into contact with the surface of the circuit board 5. , The lead 3 and the pad 6 are reflow-soldered.

[0020]

The depth of the step H on the stepped end face of the present invention is about 50 μm larger than the sum of the layer thickness of the pad and the thickness of the seating portion.

As a result, the thickness of the solder layer between the seating portion of the lead and the pad of the circuit board after reflow soldering becomes about 50 μm. Therefore, even if the temperature changes during the operation of this semiconductor device and a tensile force acts between the lead of the semiconductor component and the pad of the circuit board, the tensile stress applied to the solder becomes small because the solder layer is thick.

That is, the generation of cracks in the solder is prevented, and there is no disconnection between the leads and pads, or no connection failure.

[0023]

The present invention will be described in detail with reference to the drawings. The same reference numerals denote the same objects throughout the drawings.

FIG. 1 is a view of an embodiment of the present invention, (A) is a cross-sectional view before mounting, (B) is a cross-sectional view of a main part at the time of mounting, and FIG. 2 is a view of another embodiment of the present invention. , (A) is a cross-sectional view before mounting, and (B) is a cross-sectional view of a main part at the time of mounting.

In FIG. 1, reference numeral 40 denotes a bonding tool provided with a frame-shaped main body 41 having a rectangular cavity similar to the shape of the package 2 of the semiconductor component 1 in plan view and having a larger desired size in the lower portion of the central portion. Is.

The frame-shaped end surface at the lower end of the frame-shaped main body 41 is a stepped end surface 45 having a predetermined step H whose outer peripheral portion projects downward in a frame shape. The predetermined step H is a step that is about 50 μm larger than the sum of the layer thickness of the pad 6 and the thickness of the seat 3A of the lead 3.

The inner frame size of the outer peripheral side step end face 46 of the stepped end face 45 is more desirable (about 1 mm) than the frame size formed by the outer edges of the pads 6 arranged in a frame shape on the circuit board 5. Making it big.

To surface-mount the semiconductor component 1 on the circuit board 5 using the bonding tool 40 as described above, first, the solder paste 10A having a thickness of 70 μm to 100 μm is screen-printed on the surface of each pad 6. And apply.

Next, the semiconductor component 1 is adsorbed by a robot hand or the like (not shown), transferred onto the circuit board 5, and the leads 3 are attached.
Align the pad with the corresponding pad 6, and seat the lead 3
3A is placed on the cream solder 10A, and the semiconductor component 1 is temporarily placed on the circuit board 5.

After that, the bonding tool 40 is set to about 240 ° C.
Heating to lower the bonding tool 40, stepped end face
The inner step end surface 47 of 45 presses the upper surface of the seating portion 3A to form a stepped end surface.
The outer peripheral side step end surface 46 of 45 is brought into contact with the surface of the circuit board 5.

As a result, as shown in FIG. 1B, the cream-like solder 10A is remelted, and the solder having a film thickness of about 50 μm is formed between the lower surface of the seat 3A and the upper surface of the pad 6. As the layer is formed, the surface tension of the molten solder causes the heel 11 at the rear portion of the seating portion 3A and the fillet 12 at the front portion of the seating portion 3A, and the semiconductor component 1 is reflow-soldered on the pad 6.

By setting the thickness of the solder layer to 50 μm as described above, the tensile stress applied to the solder is reduced by 30% to 40% as compared with the conventional solder layer having a thickness of 10 μm. Therefore, according to the method of the present invention, the reliability of soldering is improved.

The bonding tool 40 shown in FIG. 2 is different from the bonding tool 40 shown in FIG. 1 in that a frame body 41 is provided with a means for sucking the semiconductor component 1. The suction means will be described in detail below.

The inner wall of the frame-shaped main body 41 is a truncated pyramid surface whose upper part is reduced, and the upper part of the truncated pyramid surface is similar to the planar shape of the package 2 of the semiconductor component 1 in plan view and is slightly larger than that. And the dish-shaped rubber 30
Is inserted, and its upper end surface is fixed to the frame-shaped main body 41 with an adhesive or the like.

Then, a hole 33 penetrating the center of the dish-shaped rubber 30 and the axis of the bonding tool 40 is provided, and the suction port of a vacuum pump (not shown) is connected to this hole 33 to drive the vacuum pump. The inner space of the dish-shaped rubber 30 is decompressed.

To surface mount the semiconductor component 1 on the circuit board 5 using the bonding tool 40 shown in FIG.
First, cream solder 10 is applied to the surface of each pad 6.
Screen print A and apply.

Next, a bonding tool heated to about 240 ° C. is placed on the semiconductor component 1 mounted on the table near the circuit board 5.
40 is moved and lowered to press the edge end surface 31 of the dish-shaped rubber 30 against the upper end surface of the package 2 of the semiconductor component 1, and the vacuum pump is driven to adsorb the semiconductor component 1 with the dish-shaped rubber 30.

Next, the bonding tool 40 is attached to the circuit board 5.
The lead 3 of the semiconductor component 1 is moved to the upper position, aligned with the corresponding pad 6, and the seating portion 3A of the lead 3 is placed on the cream-like solder 10A, and seated on the inner step end surface 47 of the step end surface 45. Press the upper surface of part 3A, and the outer peripheral side step end surface 46 of the stepped end surface 45
Are brought into contact with the surface of the circuit board 5.

As a result, as shown in FIG. 2B, the cream-like solder 10A is remelted, and the film thickness of about 50 μm is formed between the lower surface of the seat 3A and the upper surface of the pad 6. As the solder layer is generated, the surface tension of the molten solder causes the seat 3A
The heel 11 is formed on the rear portion and the fillet 12 is formed on the front portion of the seating portion 3A, and the semiconductor component 1 is reflow-soldered on the pad 6.

By using the bonding tool 40 provided with the suction means as shown in FIG. 2, there is an advantage that the work of aligning and mounting the semiconductor component on the circuit board and the soldering work can be carried out at the same time. .

[0041]

As described above, according to the present invention, by mounting a semiconductor component on the surface using a bonding tool having a stepped end face, the leads of the mounted semiconductor component and the circuit board can be mounted even when the temperature changes. The disconnection between the pads does not cause a defective connection, and has a practically excellent effect that the reliability of the connection is high.

Further, the use of the bonding tool provided with the semiconductor component suction means has the effect of significantly reducing the surface mounting work time of the semiconductor component.

[Brief description of drawings]

FIG. 1 is a diagram of an embodiment of the present invention (A) is a cross-sectional view before mounting (B) is a cross-sectional view of a main part at the time of mounting

FIG. 2 is a view of another embodiment of the present invention, (A) is a cross-sectional view before mounting, (B) is a cross-sectional view of a main part at the time of mounting

[Fig. 3] Mounting diagram of semiconductor components

FIG. 4 is a diagram showing a conventional method.

[Explanation of symbols]

1 semiconductor component 2 package 3 lead 3A lead 5 circuit board 6 pad 10 solder 10A cream solder 11 heel 12 fillet 20,40 bonding tool 21,41 frame body 30 plate-shaped rubber 45 stepped end surface 46 outer peripheral side stepped end surface 47 inside Step face

Claims (2)

[Claims] 1. When mounting a semiconductor component on a circuit board by applying cream solder to a pad provided on the surface of the circuit board and reflow soldering the lead of the semiconductor component and the pad, respectively. After the seating portion (3A) of the lead (3) is aligned with the corresponding pad (6) and the semiconductor component (1) is temporarily mounted on the circuit board (5), the frame-shaped end face Using a bonding tool (40) provided with a frame-shaped main body (41) having a stepped end surface (45) of a predetermined step (H), the stepped end surface (45) of the heated bonding tool (40) is heated. The upper step of the seating portion (3A) is pressed by the inner stepped end surface (47) of the stepped end surface (45), and the outer peripheral stepped end surface (46) is brought into contact with the surface of the circuit board (5), A surface mounting method for semiconductor parts, characterized in that the leads (3) and the pads (6) are reflow-soldered. 2. A frame for mounting a semiconductor component on the circuit board by applying cream solder to a pad provided on the surface of the circuit board and reflow soldering the lead of the semiconductor component and the pad. A frame-shaped main body (41) having a stepped end surface (45) having a predetermined step (H), and the semiconductor component inside the frame-shaped main body (41).
(1) is attached to the bonding tool (4
0) is used to carry the semiconductor component (1) by adsorbing the semiconductor component (1) into the frame-shaped body (41), and seating portions of the leads (3) respectively.
After aligning (3A) with the corresponding pad (6), the upper surface of the seating portion (3A) is heated by the inner step end surface (47) of the stepped end surface (45) of the heated bonding tool (40). Pressing the outer peripheral side step end surface (46) of the stepped end surface (45) against the surface of the circuit board (5) to reflow solder the lead (3) and the pad (6). Surface mounting method for characteristic semiconductor components.