JPS6012784B2 - Semiconductor package molding method - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to semiconductor elements such as diodes and transistors, and integrated circuits of these semiconductors (hereinafter referred to as semiconductors).
A method of molding a package for airtightly storing semiconductors, more specifically, a method of molding two thermoplastic resin plates into which semiconductors are attached, at least one of which has a pre-molded card frame, at least one of which has a recess for storing semiconductors. The present invention relates to a method for manufacturing thermoplastic resin flat packages, dual in-line packages, etc., which are sandwiched between two thermoplastic resin plates (hereinafter referred to as thermoplastic resin plates) and integrally sealed.

Traditionally, packaging methods for semiconductors include packaging methods that use metal, ceramics, glass, etc. for airtight sealing, and packaging methods using plastic. Recently, inexpensive plastic packages have become mainstream due to improved reliability due to advances in chip protection technology. It becomes. There are two types of plastic packages currently in practical use, the so-called molding method and the injection method, depending on their manufacturing method.

Among these, plastic packages made of epoxy resin transfer molding are most commonly used because of their excellent adhesion to metals, spill resistance, and electrical and mechanical properties.

In this molding method, as shown in Fig. 1, a lead frame 5 in which a pellet 2 on a tab 1 is connected to a lead 4 with a metal wire 3 such as gold or aluminum is sandwiched between an upper mold 6 and a lower mold 7. Although not shown, this is a method in which a molded resin material is filled into the cavity 8 from a transfer molding machine via a sprue, runner, and gate.

The disadvantage of this method is that the thickness of the lead frame varies,
Due to the accuracy of mold processing and wear and dimensional deviations due to use, gaps are created between the mold lead frames, and flash often appears in and around this area.The flash on these leads is There are drawbacks such as poor contact between the lead and the socket and interference with soldering work, which requires removal work.

Furthermore, with this method, the chip comes into direct contact with the molding resin material during resin sealing, exposing it to high temperature and high pressure conditions, which in some cases has the disadvantage of affecting the reliability of semiconductor functions. .

In order to improve the drawbacks of the molding method, Japanese Patent Application Laid-Open No. 5
A method such as No. 2-77669 has been proposed.

As shown in FIG. 2, this method uses a lead frame 5 on which no semiconductors are mounted, and a plastic case with a welding rib 10 and a window 9 formed in advance from thermoplastic resin.
In this method, a semiconductor chip (not shown in the figure) is housed through a window 9 of the plastic case 11 after being sandwiched between a base 11 and a plastic case 12 with a bottom and welded together using ultrasonic or high frequency waves.

However, with this method, it is necessary to incorporate the semiconductor chip through the window 9 of the plastic case 11, and then connect the semiconductor circuit leads with metal wires.
Depending on the shape and dimensions of the plastic case 11, the plastic case may become an obstacle and make wiring work difficult. In addition to problems such as the need for an airtight sealing process using a resin-like material, there are two joining parts: one between the plastic case and the lead, and the other between the plastic case and a lid-like object, or between the semiconductor chip and the resin-like object. Therefore, there were drawbacks such as affecting the reliability of the airtight seal.

In order to eliminate this drawback, as shown in FIG. 3, two thermoplastic resin plates 13 and 13', each of which is pre-formed and has at least one recess for accommodating the semiconductor, are used. Although this is not the case, thermoplastic resin plates 13, 13 are made by attaching semiconductors or sandwiching the board frame 5 between the fixed base 14 and the ultrasonic vibration tool horn 15, and then applying ultrasonic vibrations. 'Toread frame 5
A method for packaging semiconductors has also been proposed in which molten resin generated by vibrational friction between the leads is poured into the lead gaps 16 of the lead malem.

However, even in this method, there is a problem in that the following defects occur.

In other words, in the case of contact friction of a flat combined chamfer lead frame, the contact area is relatively large and a large amount of energy is required for melting, so if the ultrasonic vibration time is constant, the vibration of the tool horn will be increased. On the other hand, if the shaking is kept constant, it will take a long time to vibrate, and air will easily get caught up in the molten resin during the vibration, causing problems with airtightness as it becomes porous. At the same time, fatal problems such as deformation or breakage of the delicate cords may occur due to the ultrasonic vibration during vibration or an increase in the vibration time.

The present invention has been made in view of these drawbacks, and the details thereof will be explained below with reference to FIGS. 4 to 8 showing one embodiment.

In FIG. 4, two thermoplastic resin plates 13, 1 are formed in advance and have at least one (in FIG. 4, both) recesses 17, 17' for accommodating semiconductors.
3' sandwich the board frame 5 on which semiconductors (not shown) are mounted, and after preheating these to a predetermined temperature at least before ultrasonic vibration, the tool horn 15
The thermoplastic resin plates are fused together by ultrasonic vibration.

At this time, depressions 17, 17' are formed on the base surfaces 18, 18' located on the combined surface side of at least one of the two thermoplastic resin plates 13, 13' (both in FIG. 4). A thermoplastic resin plate-like body having one continuous convex portion surrounding it is used.

If one of the plate-shaped bodies does not have a recess, a thermoplastic resin plate having one continuous convex part that surrounds the part corresponding to the concave part of the paired thermoplastic resin plate-shaped body. Use your body. When ultrasonic vibration is applied to the plate-like body through the tool horn 15, the convex portion in contact with the lead frame 5 first melts due to vibration friction, the molten resin flows into the lead gap 16 of the lead frame 5, and then the convex portion As the melting progresses, the base surface 18 and the surface 2 of the lead, as partially shown in FIG.
The void 2 other than the volume occupied by the convex portion 19 formed between the
The molten resin flows into 1, and also flows into the burr reservoir 22, which was intended in the design, as shown in FIG.
The leads are sandwiched between two thermoplastic resin plate-like bodies and are integrally sealed.

What is important in this case is that the surfaces 20 of the joined leads are not brought into contact with the base surface 18 of the convex portion located on the joining surface side of the two thermoplastic resin plates.

As a result, there is a gap 2 between the front and back surfaces of the lead and the base surface.
1 is secured.

A portion of the resin melted by ultrasonic vibration flows into this gap and is fused with the surrounding resin.

In order to obtain sufficient airtight deposition in ultrasonic deposition, it is necessary to secure a melting volume of at least a certain volume in order to reach the temperature of the molten melt above a certain level. This is an essential condition in order to secure the above melting volume and achieve airtightness. If this gap is not provided, the minimum volume that needs to be melted by ultrasonic vibration is the total volume of the lead gap corresponding to the projection of the thermoplastic resin plate to the lead frame excluding the recessed part. The combined volume of the total volume of the burr reservoir should be sufficient as intended in the design, but it varies depending on the dimensions and shapes of the lead frame and plate-like body, but as shown in the example of the 16-pin DIP shown in Fig. 6, For example, this total volume is approximately 1.4 × 10-2,
For one thermoplastic resin plate, half of that is 7×
The shape of the convex part is shown in Fig. 7 (
(a is a plan view, b is a cross-sectional view of AL-1, c is a cross-sectional view of A-row), and the height is about 170 m at most, which requires airtightness due to the ultrasonic capacity. It becomes so small that it cannot function satisfactorily as a landing protrusion in the case of a target. The main point of the present invention is that when a molten resin volume greater than a certain volume necessary to reach the temperature of the molten body above a certain level and maintain it around this temperature for a certain period of time or more is secured, {11 A convex portion is provided only on the combined surface side of at least one of the two thermoplastic resin plates.

{21 A convex portion capable of competing with the lead gap of the lead frame is provided on at least one of the two joining surfaces.

'3' The lead frame is combined without contacting at least one base surface of the thermoplastic resin plate.

In any of the above three cases, a preferable airtight union is achieved. Further, from the same point of view, as long as the void is substantially filled with the molten resin of the convex portion, the base surfaces 18, 18' of the convex portions 19, 19' do not need to be flat, and therefore the volume of the void 21 may vary depending on the location, and depending on the shape of the thermoplastic resin plate, better airtight welding performance may be obtained by intentionally varying the shape and arrangement of the convex portions and therefore the voids. There is also.
That is, in the present invention, a protrusion is provided on the combined surface side of the thermoplastic resin plate, and the surface of the lead (the plane shown in FIG. 6 or its back surface) is connected to the base surface (thermoplastic resin (which is considered to be the surface with the largest cross-sectional area of the plate), a part of the molten resin on the convex part is absorbed into the gap between the base beveled surface of the plate and the surface of the plate. The purpose is to ensure that the amount of molten resin is greater than a certain volume necessary to obtain a good coalescing state.

FIG. 8 is a perspective view showing the semiconductor package after being assembled. Preheating the thermoplastic resin plate-shaped lead frame is an important requirement in order to make the ultrasonic vibration conditions the gentlest and to eliminate any deformation or damage to the lead frame when assembled. Although the process differs depending on the material and shape of the plate-shaped body and the lead frame, it is generally carried out at a temperature and time below the upper limit that does not cause deformation that adversely affects the thermoplastic resin plate-shaped body.

Furthermore, on the other hand, it is necessary that the temperature and time be within an upper limit that does not impair the functions of the semiconductors mounted on the lead frame, and below the upper limit temperature and time that will not cause oxidation or damage to the lead frame. Although ultrasonic vibration has been described above as a heating means, means such as hot plate assisted heating and hot air heating may also be used.

Various types of thermoplastic resins are used in the present invention depending on the characteristics required for each semiconductor package. Electricity above a certain level,
In addition to mechanical properties, it is also necessary to have moldability above a certain level.

Typical examples include ether resins such as polyphenylene oxide, polyether sulfon, polysulfone, phenoxy resin, and polyacetal, ester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyarylate, carbonate ester resins such as polycarbonate, Examples of polyamide resins include grades with low water absorption, resins such as polyphenylene sulfide, and combinations of some of these resins and fillers, mainly glass fibers.

Example heat distortion temperature (ASTM D-64818.6k9
The thermoplastic resin plate-like body having the shape and dimensions (unit rib) as shown in Fig. 7 and the thickness (d in Fig. B) of 1.18 willow using a polyarylate resin with a diameter of 17yo 200002 After molding a thermoplastic resin plate with the same shape and dimensions as shown in the figure, sandwiching a 250mm thick 16-pin DIP lead frame with a semiconductor chip attached, and attaching a flexible heat-resistant material to prevent burrs around it.200002 Heating was carried out for a minute.

Next, this is set to an oscillation frequency of 19. Using a rectangular tool horn with an end size of 2 mosquitoes x 7 skins attached to an ultrasonic welding machine with an output of 30 Hz and an output of 30 skin, apply a pressure of 4k9/ground from the thick thermoplastic resin plate side to the tip of the tool horn. The club's average is 35
After adjusting the swing to make it perfect, it is 0. Ultrasonic oscillation was performed between the neck and the sand.

The length of the obtained combined product in the thickness direction from the lead surface is 2.2 mm and 1.5 mm on the front and back, respectively, and the overall thickness is 3.5 mm.
It was on the 95 side. Almost no burrs that could be an obstacle were observed on the outer periphery and in the recessed areas. The obtained semiconductor package was subjected to a pressurized red water immersion test of 5k9/base and 2 ponds, and no red matter was observed to enter the package.
It was confirmed that it had good sealing properties. Also, no deformation or breakage of the lead was observed. In this example, the convex portion having a height of 0.9 ribs shown in FIG.
It was 0-2. The total volume of the convex portion of the comparative example is expressed as the total volume of the lead gap corresponding to the projected portion of the thermoplastic resin plate with respect to the lead frame excluding the recesses 17 and 17' shown in FIG. 7, and the total volume of the lead gap shown in FIG. The assembly was carried out under the same conditions as in the example except that the total volume of the burr reservoir 22 was set to 1.4 Ultrasonic oscillation for 1.5 seconds or more was required to achieve a state in which it was not possible to obtain a state in which it could be considered that they had coalesced in appearance.

In this case, the depressions 17 and 17' were filled with resin containing air bubbles, making it impossible to secure the volume of the depressions, and deformation of the lead frame and breakage of the leads were observed.

Incidentally, the total amount of molten resin in this case was 1.4 x 10-2 flow.

As explained above, the following effects are achieved in the present invention.

○'By using a thermoplastic resin plate-like body, at least one of which has a recess for storing semiconductors, there will be no damage to the connections between the semiconductors and the leads when the package is molded together. Since high temperatures and high pressures are not applied to semiconductors, it is difficult for ionic substances to come into contact with them, so it is expected that the reliability of semiconductor functions will improve.

{2) By combining the lead frames at a position that does not touch the base surface of the protrusion provided on the combined surface side of at least one of the two thermoplastic resin plates, a gap is created between the leads and the base surface. As a result, in ultrasonic welding, it is possible to melt a resin volume greater than a certain amount required to reach a certain level of temperature, and as a result, airtightness is improved.

[3' By heating the thermoplastic resin plate and lead frame to a certain temperature prior to ultrasonic vibration and providing a melting convex portion, the conditions for ultrasonic vibration, that is, the duration and time of vibration, can be reduced or This has improved the problem of deformation and breakage of the delicate and fragile 1' board frame.

■ By relaxing the ultrasonic vibration conditions mentioned above, air bubbles are less entrained in the molten resin and airtightness is improved, while the occurrence of burrs is reduced, making it easier to secure the volume of the recess for storing semiconductors.

[5} Similarly, relaxing the ultrasonic vibration conditions led to a reduction in welding work time. '61 The present invention has made it possible to automate the assembly of semiconductor packages.

'7- Compared to the conventionally proposed method in which a lead frame without semiconductors attached is combined with a molded product with a window and a molded product with a bottom, semiconductors are incorporated and the window is further sealed. In the method of the present invention, a completely airtight semiconductor package can be formed by a single combined molding process, thereby simplifying the process.

'8} Compared to the conventional mold sealing method using thermosetting resin, the resin viscosity during molding can be kept high, so there is almost no burr generation during molding, and the process can be reduced.

[Brief explanation of the drawing]

1, 2, and 3 are cross-sectional views showing a conventional semiconductor package molding method, and FIGS. 4 to 8 are views showing an embodiment of the present invention, and FIG. 4 is a cross-sectional view. , FIG. 5 is an enlarged sectional view of a part of FIG. 4, FIG. 6 is a plan view of a package including a lead frame, and FIG. 7 is a plan view a and a sectional view showing the shape and dimensions of the thermoplastic resin plate. Figures b, c and 8 are perspective views of a semiconductor package obtained by the method of the present invention. Explanation of symbols, 1...Tab, 2...Semiconductor chip, 3...Metal wire, 4...
Lead, 5...Lead frame, 6...
・Upper die, 7...Lower die, 8...Cavity, 9...Window part, 10...Rib for dropping, 11.
...Plastic case, 12...Plastic case with bottom, 13, 13'...
Thermoplastic resin plate-shaped body, 14...Fixing stand, 15...
...Ultrasonic vibration tool horn, 16... Lead gap, 17, 17'... Hollow, 18, 18'.
...Foundation surface, 19, 19'...Protrusion, 20...Lead surface, 21...Void, 22...
Bali reservoir, 23...Package. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Groove diagram Figure 8

Claims (1)

[Scope of Claims] 1. A thermoplastic resin plate-shaped molded product is sandwiched between two thermoplastic resin plate-shaped molded products, at least one of which has a recess for accommodating semiconductors, and a lead frame on which semiconductors are mounted is sandwiched between two thermoplastic resin plate-shaped molded products, at least one of which has a recess for accommodating semiconductors. In a package molding method for semiconductors in which heat fusion is carried out, if at least one thermoplastic resin plate-shaped molded product has a depression on the joining surface side, the molded product is formed so as to surround the depression; If there is no depression, a continuous convex part is provided that surrounds the part corresponding to the concave part of the paired thermoplastic resin plate-shaped molded product, and the base surface of the convex part is the surface of the lead frame. A method for molding packages for semiconductors, which is characterized in that they are combined at positions where they do not come into contact with each other. 2. A method for molding a semiconductor package according to claim 1, characterized in that thermoplastic resin plate-shaped molded products are heated and fused together by ultrasonic vibration. 3. A method for molding a package of semiconductors according to claim 1 or 2, characterized in that at least one of the lead frame and the thermoplastic resin plate-shaped molded product is preheated before being heated and fused together. . 4 A part of the molten resin of the convex part is formed between the base surface of the convex part provided on the combined surface side of at least one of the two thermoplastic resin plate-shaped molded products and at least one surface of the lead frame. A method for molding a semiconductor package according to claim 1, 2 or 3, characterized in that the voids are substantially filled.