JPS6019662B2 - 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 package forming method for airtightly storing semiconductors, more specifically, at least one pre-formed card frame in which semiconductors are mounted has a recess whose peripheral side wall thickness varies depending on the position for storing semiconductors. A flat package and a dual in-line package made of thermoplastic resin, characterized in that the two pieces are sandwiched between thermoplastic resin plate-shaped molded products (hereinafter referred to as thermoplastic resin plate-shaped bodies) and are integrally sealed. It is related to the manufacturing method.

Traditionally, packaging methods for semiconductors include packaging methods that use metal, ceramics, glass, etc. for airtight sealing, and packaging methods that use plastic.Recently, with improvements in reliability due to advances in chip protection technology, inexpensive plastic packages have become popular. It's becoming mainstream. 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 by transfer molding of epoxy resin, which have excellent adhesion to metals, moisture resistance, and electrical and mechanical properties, are most commonly used.

In this molding method, as shown in Fig. 1, a semiconductor chip 2 on a tab 1 is connected to a lead 4 using a metal wire 3 made of gold or aluminum.
The lead frame 5 connected to the upper die 6 and the lower die 7
Although not shown, the sprue, runner,
In this method, a molded resin material is filled into the cavity 8 from a transfer molding machine through a gate.

The disadvantage of this method is that due to variations in the thickness of the lead frame, precision of mold processing, wear due to use, and dimensional deviations, gaps are created between the lead frames of the mold, and flash occurs in and around this area. In many cases, the flash on these leads causes poor contact between the leads and the socket and hinders soldering work, resulting in the need for removal work.

Furthermore, this method has the disadvantage that the chip is exposed to high temperature and pressure during direct contact with the molding resin material during resin sealing, which may affect the reliability of the semiconductor function in some cases. Ta.

In order to improve the drawbacks of this molding method, Hakama Sekisho 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 attached, a plastic case 11 with a port lip 10 and a plastic case 12 with a bottom, which has a window 9 molded in advance from thermoplastic resin. This is a method in which a semiconductor chip (not shown in the figure) is housed through the window 9 of the plastic case 11 after being welded and integrated using sandwiched ultrasonic waves or high frequency waves.

However, in this method, it is necessary to install the semiconductor chip 2 through the window 9 of the plastic case 11 and then connect the semiconductor circuit leads with metal wires. , the plastic case may become an obstacle and make wiring work difficult.Even if there is no problem with wiring, the window 9 of the plastic case 11 must be sealed airtight with another lid-like object or resin-like object after wiring. In addition to problems such as the need for a sealing process, there are two joints: one between the plastic case and the leads, and the other between the plastic case and a lid-like object, or between a semiconductor chip and a resin-like object, so the airtight seal cannot be achieved. - There were drawbacks such as affecting the reliability of the system.

In order to eliminate this drawback, as shown in FIG. 3, two thermoplastic resin plates 13, 13', each of which is pre-formed and has at least one recess for accommodating the semiconductor, are used. However, the thermoplastic resin plate-like bodies 13, 13 are made by sandwiching the semiconductors and the board frame 5 between the fixed base 14 and the ultrasonic vibration tool horn 15, and then applying ultrasonic vibration. 'Toread frame 5
A method for packaging semiconductors has also been proposed in which molten resin generated by vibrational friction between the lead frames is caused to flow into the lead gaps 16 of the lead frame.

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

That is, in the thermoplastic resin plate-like body 13 having the shape shown in FIG. 4, a is a cross-sectional view, and FIG. The located joining surface 18 first melts due to frictional heat generation, and when the thick side wall portions 19 and 19' are completely fused, the thin side wall portion 17 swirls and melts, so a hole is created in this portion. Serious deficiencies occasionally occurred.

In addition, in the case of contact friction between the flat joining surface and the IJ 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 reduced. On the other hand, if the vibration is kept constant, air is likely to get caught up in the molten resin during the vibration because it requires long vibrations, and the molten resin becomes porous, which sometimes makes it impossible to make it airtight. This sometimes caused problems.

Further, during the ultrasonic vibration or when the vibration time increases, fatal problems such as deformation or breakage of the delicate cords may occur.

The present invention has been made in view of these points, and its contents will be explained below with reference to FIGS. 5 to 9 showing one embodiment.

In FIG. 5, there are two pre-formed recesses 20, 20' having thin side walls 17, 17' and thick side walls 19, 19' at the periphery, at least one of which is for accommodating semiconductors. A board frame 5 on which semiconductors (not shown in the figure) are mounted is made of thermoplastic resin plates 13 and 13'.
After sandwiching and preheating these to a predetermined temperature (it is sufficient that the child heating is done at least before the ultrasonic vibration), the thermoplastic resin plates are fused by ultrasonic vibration by the ultrasonic vibration tool horn 15. Combine.

At this time, the merging surfaces 18, 18' are substantially parallel to the rigging surfaces 18, 18' on the thick side wall portions, excluding the merging surfaces 18, 18' located on the thin side wall portions of the package formed by the recesses.
Convex portions 22, 22 protruding from the rigging body surfaces 18, 18' are provided on the reference surfaces 21, 21' located inside the rigging body surfaces 18, 18'.
A thermoplastic resin plate having a plurality of ′ is used.

When ultrasonic vibration is applied to the plate-like body through the tool horn 15, the convex portions 22, 22' in contact with the lead frame 5 are first melted by vibration friction, and the molten resin flows into the lead gap 16 of the lead frame 5. Next, the convex portions 22, 22' are melted to form the joining surface 1 of the thin side wall portions 17, 17'.
8 and 18' come into contact with the lead frame 5, and this portion heats up and melts due to friction.

Furthermore, as the convex parts 22, 22' melt, as partially shown in FIG. The molten resin flows into the burr reservoir 25 that was intended in the design as shown in Fig. 7, and finally the lead is sandwiched between two thermoplastic resin plates and sealed together. be done.

At this time, both the front and back surfaces 23, 23' of the joined leads are the protrusions 2 located on the thick side walls of the two thermoplastic resin plate-shaped molded products.
2, 22' must be joined at a position that does not touch the reference surfaces 21, 21'. This ensures a gap between both the front and back surfaces of the lead and the reference surface. A portion of the resin melted by ultrasonic vibration flows into this gap and is fused and integrated with the surrounding resin.

In order to obtain sufficient airtight welding in ultrasonic deposition, it is necessary to secure a melting volume of at least a certain volume in order to raise the temperature of the fused body to a certain level. This is a necessary 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 thick side wall and thin side wall onto the IJ card frame, and the total volume of the designed burr reservoir. However, in the example of a 16-pin DIP lead frame, this total volume is approximately 1.3 If we consider the case of arranging 32 uniformly shaped square bells, which are extremely small (6.5 x 10-3 per resin plate), the height of the square pyramids is about 250r, and ultrasonic welding is difficult. In some cases, the welding protrusion becomes so small that it cannot function sufficiently as a welding protrusion.

Incidentally, if the lead frame is joined together without contacting only one reference surface of the molded thermoplastic resin plate product, the purpose may be sufficiently achieved in some cases. In addition, making the convex part protrude beyond the joining surface located on the thin side wall is a necessary condition to prevent damage due to excessive melting to the thin side wall near the center where stress tends to concentrate due to ultrasonic vibration. be. In this case, from the viewpoint of function, the convex portion lower than the convex portion located on the thick side wall portion 19 is placed on the combined surfaces 18 and 1 corresponding to the thin side wall portion 27.
8' also does not impair the functionality of the present invention. Although it is desirable to provide the convex portions in a dispersed state as much as possible, the position, shape, etc. may be appropriately determined within a range that does not impair the function of the present invention due to issues such as the shape of the lead frame and the appearance of the package. can.

The convex portion is provided on at least one of the thermoplastic resin plate-shaped molded products having a recess for accommodating semiconductors.

Preheating the thermoplastic resin plate and the IJ lead frame is an essential requirement in order to keep the conditions of ultrasonic vibration at the gentlest level and to eliminate any deformation or damage to the lead frame during assembly. Although it varies depending on the material and shape of the shaped body and the lead frame, generally the temperature and time are below the upper limit at which deformation that adversely affects the thermoplastic resin plate does not occur.

Furthermore, it is necessary that the temperature and time be within an upper limit that does not impede the functions of the semiconductors mounted on the lead frame, and below the upper limit temperature and time that do not cause oxidation or anchoring in the lead frame.

Various types of thermoplastic resins are used in the present invention, depending on the characteristics required for each semiconductor package. In addition to electrical and mechanical properties that exceed standards, it is also necessary to have moldability that exceeds a certain level. Typical examples include polyphenylene oxide, polyether sulfone, polysulfon, phenoxy resin, ether resins such as polyacetal, polyethylene terephthalate, polybutylene terephthalate,
Ester resins such as polyarylate, carbonate ester resins such as polycarbonate, grades with low water absorption among polyamide resins, resins such as polyphenylene sulfide, and some of these resins and fillers mainly made of glass fiber. It is possible to list combinations of. Example
1 Heat distortion temperature (ASTM○164818.6k9/earth)
A plate-shaped body with the shape and dimensions as shown in Fig. 8 is made using polyarylate resin with a diameter of 17 p0, A = 1.28 side in Fig. 8, B
= 1. A thermoplastic resin plate with the same shape and dimensions except for the first leg is molded, a 16-pin DIP type lead frame with a thickness of 250 threads on which a semiconductor integrated circuit is mounted is sandwiched, and a burr prevention material is placed around it. After attaching the flexible heat-resistant material, heating was performed for 200q02 minutes.

Next, this is set to an oscillation frequency of 19. Cruise HZ, output 300W
Using a tool horn with an end shape of 20 x 7 ribs attached to an ultrasonic welding machine, a pressure of 4k9/ground was applied from the thick thermoplastic resin plate side, and the vibration at the tip of the tool horn was 351. After adjusting the shaking mode as shown below, 0. Ultrasonic oscillation was conducted between the existing sand.

The length of the resulting combined product in the thickness direction from the lead surface is 2.2 and 1.5 willow on the front and back, respectively, and the total thickness is 3.
It was 95 willow.

Almost no burrs that could be an obstacle were observed on the outer periphery and in the recessed areas. The obtained semiconductor package is 5k9/
Even in the pressurized red water test at 2 small r, no red matter was observed to enter the package, confirming that it had good airtightness. Comparative Example 1 A semiconductor package was manufactured under the same conditions as in Example 1, except that a convex type having the same height as the convex portion provided on the combined surface of the thick side wall was provided on the combined surface located on the thin side wall. However, due to excessive melting of the thin side wall, small holes were formed and good airtightness could not be obtained.

Comparative Example 2 When a semiconductor package was manufactured under the same conditions as Comparative Example 1 except that the heating for 200q02 minutes was not performed, it was found that the fusion was insufficient. A breakage was observed.

Comparative Example 3 A semiconductor package was manufactured under the same conditions as in Example 1 except that the convex portion was provided on the thick side wall on the same plane as the joining surface located on the thin side wall. Breakage of the leads was observed as well as penetration, and the thickness of the combined product was only smaller than the specified size.

Comparative Example 4 A semiconductor package was manufactured under the same conditions as Example 1 except that it had no protrusions and had a thick side wall joining surface that was flush with the joining surface that was placed on the thin side wall. Ultrasonic oscillation for 2 seconds or more was required for the state to be considered as merging.

In this case, the depression was filled with resin containing air bubbles, making it impossible to secure the volume of the depression, and breakage of the deformed leads of the IJ-deframe was observed.

As explained above, the following effects are achieved in the present invention. '11 By using a thermoplastic resin plate, at least one of which has a recess for accommodating semiconductors, there will be no damage to the connections between the semiconductors and the leads when molding the package 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} Ultrasonic welding is achieved by providing a convex portion only on the thick side wall of the thermoplastic resin plate, excluding the combined surface located on the thin side wall, and by making the convex portion protrude beyond the combined surface. During assembly, the phenomenon of holes caused by excessive melting of the central thin side wall was eliminated, and the airtightness was improved.

By providing the '3' convex portion on the reference surface located inside the joining surface located on the thin side wall, a gap is secured between the front and back surfaces of the reference surface lead, which allows In sonic tethering, it is possible to melt a volume of resin exceeding a certain amount necessary to bring the temperature of the melted body above a certain level, and as a result, the airtightness is improved.

'4) By heating the thermoplastic resin plate and lead frame to a constant temperature prior to ultrasonic vibration and by providing a melting convex portion, the conditions for ultrasonic vibration, that is, the duration and time of vibration, are reduced. Or it can now be shortened, and problems such as deformation and breakage of delicate and fragile folded frames have been improved.

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

'6} Similarly, relaxing the ultrasonic vibration conditions led to a reduction in welding work time. '71 The present invention has made it possible to automate the assembly of semiconductor packages.

[81] Compared to the conventionally proposed method of combining a lead frame with no semiconductors attached with a molded product with a window and a molded product with a bottom, incorporating semiconductors and sealing the window, this method is more effective. In the method of the invention, a completely airtight semiconductor package can be produced by a single combined molding process, thereby simplifying the process.

[9- Compared to the conventional mold sealing method using thermosetting resin, the resin viscosity during molding can be kept high, so it is possible to maintain a high resin viscosity during molding.
There is almost no occurrence of cracks and the process can be reduced.

[Brief explanation of the drawing]

Figures 1, 2, 3, and 4 show the conventional semiconductor package molding method. Figure 4b is a bottom view, the others are cross-sectional views, and Figures 5 and 6 are main views. FIG. 7 is a plan view of a package including a lead frame; FIG. 8 is a plan view and side view showing the shape and dimensions of a thermoplastic resin plate according to an embodiment of the invention; FIG. 9 are perspective views of semiconductor packages 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 mold, 7 ... Lower mold, 8
...Cavity, 9...Window, 10.
...Welding rib, 11...Plastic case, 12...Plastic case with bottom, 13, 13'...Thermoplastic resin plate, 1
4... Fixed stand, 15... Ultrasonic vibration tool horn, 16... Lead gap, 17, 17'...
...Thin side wall part, 18, 18'... Combining surface located on the thin side wall part, 19, 19'... Thick side wall part, 20, 20'... Recess, 21, 21'...
Reference plane, 22, 22'...Protrusion, 23, 23'
......Front and back surfaces of the lead, 24...Gap, 25
...Flash reservoir, 26...Package, 27...Flash in the burr reservoir. Figure 2 Figure 3 Figure 4 Figure 5 Hakama Figure 6 Figure 8 Figure 9

Claims (1)

[Scope of Claims] 1. Semiconductors can be stored by two thermoplastic resin plate molded products, at least one of which has a recess for accommodating semiconductors, and the thickness of the peripheral side wall of the recess differs depending on the position. In the package molding method for semiconductors, in which thermoplastic resin plate molded products are fused together using ultrasonic vibrations by sandwiching a lead frame equipped with A thermoplastic resin having a plurality of convex portions protruding from the combined surface of the thin side wall portion on a reference plane that is substantially parallel to and located inside the combined surface of the thin side wall portion in the removed thick side wall portion. A semiconductor package molding method characterized by using a plate-shaped molded product. 2. The method for molding a semiconductor package according to claim 1, wherein at least one of the lead frame and the thermoplastic resin plate-shaped molded product is preheated before applying ultrasonic vibration. 3. A package for semiconductors according to claim 1, characterized in that the front and back surfaces of the lead frame are joined together at a position where the front and back surfaces of the two thermoplastic resin plate-shaped molded products do not touch the reference surfaces of the thick side walls. Molding method. 4. The method according to claim 3, characterized in that a part of the molten resin of the convex portion fills the gap formed between the reference plane of the two plate-shaped molded products and both the front and back surfaces of the lead. Method for molding semiconductor packages.