JPS6320378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for assembling a semiconductor device, and more particularly to a mounting method using a conductive adhesive.

The mounting process is divided into three steps: applying a conductive adhesive onto the lead frame, spreading the conductive adhesive, and placing the semiconductor pellet on the lead frame. Methods for applying the conductive adhesive onto the lead frame include a stamp method, a screen printing method, and a dispenser method. The stamp method uses a stamp to transfer the conductive adhesive to the lead frame, but because the top surface of the conductive adhesive in the container is always in contact with air, the viscosity tends to change, making pellet mounting difficult. The disadvantage is that it is difficult. In addition, the screen printing method is a method in which conductive adhesive is applied onto the lead frame using a rubber spatula from above the mimeograph plate with holes drilled only in the areas where the conductive adhesive is to be applied. The disadvantage is that there is a large amount of waste because a conductive adhesive must be applied. Compared to these methods, the dispenser method uses air pressure to inject conductive adhesive onto the lead frame from a thin nozzle, so the addition rate of conductive adhesive is small and work efficiency is high, and it is currently the mainstream method. is occupying. However, when the conductive adhesive is applied to the lead frame, its shape becomes spherical due to surface tension, and if the semiconductor pellet is mounted in this state, the conductive adhesive will creep up to the sides of the pellet, causing problems. arise. In particular, LED pellets with exposed junctions on the sides of the pellet are likely to cause short circuits. Conventionally, nitrogen gas was sprayed vertically from directly above the conductive adhesive to stretch it, but even with this, the conductive adhesive did not spread evenly and flatly, leaving a concave shape in the center. Adhesive continued to creep up on the side surfaces of the pellets, reducing yield.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method that eliminates the above-mentioned drawbacks, enables stable pellet mounting, and improves yield.

In the present invention, after applying a conductive adhesive to a lead frame, for example, nitrogen gas is sprayed diagonally above the adhesive at an angle of 30 to 60 degrees from the vertical direction of the lead frame, thereby creating a flat and uniform thickness. It is designed to have a thin adhesive surface.

Therefore, when spraying from a vertical direction, the adhesive does not spread flatly, but when spraying from an oblique direction, pressure can be applied in a fixed direction, resulting in a uniform thickness that spreads flatly. An adhesive layer can be obtained.

Next, the present invention will be explained based on embodiments with reference to the drawings.

As shown in Figure 1, approximately 0.1 mg of silver paste 11 is applied to the lead frame 12 using a dispenser method.
After coating the silver paste on the lead frame, the nozzle tip is fixed at a distance of 1 cm from the silver paste on the lead frame using a nozzle 13 having an inner diameter of 1 mmφ. Here, the viscosity of the silver paste used was such that the injection speed was specified as 1.9±0.3 g/min. when a pressure of 60 P.SIG was applied from a 1/2 inch long #21 needle. In addition, as a result of spraying nitrogen gas vertically toward the edge of the silver paste on the lead frame at a spray pressure of 1.0 to 3.0 kg/cm ² , the silver paste 11'' became flat as shown in Figure 2 b. Therefore, as shown in Figure 1, the nozzle was angled at an angle of 30 to 60 degrees (θ) from the vertical direction, and the nitrogen injection pressure was set at 2.5 kg/cm ² .
When the amount of silver paste was about 0.1 mg, it was possible to obtain a silver paste layer 11' that spread well in the horizontal direction like an elbow and had a uniform thickness (FIG. 2a). When we glued a 0.3mm□ GaP LED pellet to this state and observed the side surface using a microscope (x50), we found that conventionally, at least 2 to 3 out of 100 pieces of silver paste bulged out with a size of 0.2mm or more. was seen, but
As a result of using this method, it was confirmed that all silver paste creep-up was kept to 0.1 mm or less, and the final product yield improved from 92% to 97%.

As explained above, according to the present invention, it is possible to spread the silver paste flat with a uniform thickness and prevent it from creeping up to the sides of the pellets and from tilting the pellets themselves, so that the yield can be significantly improved. .

In the above example, an example was described in which silver paste was applied using a dispenser method, but the application is not limited to the type of silver paste supply method such as a stamp method or a screen printing method. Needless to say, the present invention is also fully applicable to the use of adhesives and non-conductive adhesives, and to the use of base materials other than lead frames, such as stems and printed circuit boards.

[Brief explanation of the drawing]

FIG. 1 is a front view showing the position of a nitrogen spray nozzle in an embodiment of the present invention, FIG. 2 a is a cross-sectional view of a conventional silver paste layer, and FIG. 2 b is a cross-sectional view of a silver paste layer according to this embodiment . 11, 11', 11''...Silver paste, 12...
Lead frame, 13...Nitrogen nozzle, θ...Blowing angle (30 to 60°).

Claims (1)

[Claims] 1. A conductive paste is added to one flat main surface of a substrate for mounting a semiconductor element, and the applied conductive paste is tilted 30 to 60 degrees toward the one main surface from a direction perpendicular to the one main surface. A semiconductor characterized in that the conductive paste is uniformly spread on the one main surface of the base material by injecting gas from an oblique direction, and a semiconductor element is placed and bonded thereon. How to assemble the device.