JPH04218931A - Manufacturing method of semiconductor plastic package - Google Patents

Abstract

PURPOSE:To reduce a residual stress and rationalize a production, by molding a lead frame mounting chips with a resin through a molding machine, and by heating, after mold opening, packages in succession through a heating mechanism, and further, by cooling, after hardening the resin through a reaction, the packages. CONSTITUTION:A package 22 molded by a transfer molding machine 21 is taken out from a metallic mold, and is put on the surface 24 of a carrying road, and further, far infrared rays are projected on it from its upper and lower side by a heating apparatus 25. In this process, the hardening reaction of a resin proceeds and its material quality is made stable. Then, the packages 22 irradiated in a heating way are moved on the surface 24 of the carrying road, and are stored in a heating storage apparatus 26. Then, the packages 22 are cooled in succession, and unnecessary objects such as a gate, are separated from them in the next process.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to semiconductor plastic packages, and in particular, to optimally manage and control the temperature of molded products after molding, to streamline production in the secondary curing process, and to achieve consistency. The present invention relates to a method of manufacturing a package that is automated and suitable for making products highly reliable.

[Conventional technology]

In the conventional molding process for semiconductor plastic packages, as shown in FIG. 1(a), an upper mold 2 and a lower mold 3 are heated to a high temperature (160 to 250°C) in advance, and an element 11 is placed on the lower mold 3. Set the mounted lead frame 9.

Thereafter, the upper mold 2 and the lower mold 3 are clamped, and the resin tablet 1 is put into the pots 4 of the upper mold 2 and the lower mold 3. Next, as shown in FIG. 1(b), when the resin tablet 1 is pressed by the plunger 5 and injected into the upper mold 2 and the lower mold 3, the heated and melted resin tablet 1 is poured into the runner 6 and the gate 7.
The liquid flows through the cavity 8 formed by the upper die 2 and the lower die 3 onto the lead frame 9 on which the element 11 is mounted. When filling of resin tablet 1 is completed, upper mold 2 and lower mold 3
The resin is heated for a predetermined time (30 to 90 seconds) to harden the mold and the mold is completed. Next, as shown in FIG. 1(o), the plunger 5 is pulled out, the upper mold 2 and the lower mold 3 are opened and ejected, and a molded product 12 is obtained from the lower mold 3 using a bottle 10.

Next, this molded product is taken out from the mold by a loader, and unnecessary parts such as the runner and gate are separated by a gate break.

At this time, it is difficult to break the gate unless the temperature of the molded product (gate) is lowered, so the gate is broken after lowering the temperature of the molded product by blowing air. Once the unnecessary parts are removed, the finished products are stored in racks until a certain amount is reached, so the temperature of the finished products remains the same as room temperature. When a certain amount of product accumulates on the rack, the process moves to the next step, the secondary curing process.

This is intended to stabilize the physical properties of the product, and heat treatment by patch treatment is performed at high temperature for a long time (160-250°C x 5-6 hours) using a hot air circulation furnace.

Once the heat treatment is complete, the finished product is removed from the furnace and moved on to the next process. The finished product at this time will be allowed to cool naturally to the same temperature as room temperature. FIG. 2 shows each manufacturing process before and after the molding process. Documents related to these processes and devices include Oki Electric Research and Development No. 133, ``Development of automatic integrated molded IC assembly system ``Izanagi.''

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into account thermal stress, etc. that occur inside the package due to temperature changes during the manufacturing process in the semiconductor plastic package. In particular, after the molding process is completed, in order to perform a gate break while the physical properties of the resin are not stable, air is blown onto the molded product to rapidly cool it to a certain temperature (50 to 80°C). For this reason, large stress is generated inside the molded product, which causes defects such as package cracks, interfacial peeling, and deformation, which has become a problem. In addition, the cooling during the secondary curing process is done by natural cooling, which causes large residual stress in the molded product. Furthermore, in the secondary curing process, heat treatment by patch treatment is performed at high temperature for a long time (usually 160 to 250℃) using a hot air circulation furnace.
x5 to 6 hours), this poses a problem in achieving integrated automation with the molding process, unmanned operation, and rationalization of production.

An object of the present invention is to provide a method for manufacturing a semiconductor plastic package with low residual stress by optimally controlling the thermal process applied to a molded product from the molding process to the completion of the secondary curing process, and to provide a method for manufacturing a semiconductor plastic package with low residual stress. The aim is to perform processing efficiently and in a short time, to achieve integrated automation of the semiconductor manufacturing process, rationalization of production, and unmanned production.

[Means to solve the problem]

In order to achieve the above object, the present invention uses thermoviscoelastic stress analysis simulation to optimally control the temperature process during cooling, where thermal stress is applied to the molded product, in the molding process and secondary curing process of semiconductor plastic packages. This minimizes the stress generated inside the molded product. In addition, this thermoviscoelastic stress analysis simulation is used to find the correlation between the stress value at which defects occur, the cooling rate, and the cooling temperature, and this is utilized for temperature process control of molded products. moreover,
Conventionally, we have eliminated the rapid cooling for gate breaking in a state where the physical properties of the resin immediately after molding are not stable, as described in technology, and the rack storage at room temperature after molding, and have stabilized the physical properties of the resin through secondary curing. Later, we developed a manufacturing method and equipment by moving the manufacturing process, such as cooling the gate break, and making the molding process and secondary curing process continuous.

In order to continuously and consistently automate the molding process and the secondary curing process, it is necessary to perform the heat treatment in the secondary curing process efficiently and in a short time. Therefore, new heating methods such as far infrared heating are used for the heat treatment in the secondary curing process, and other heating methods such as hot air heating, infrared heating, microwave heating, high frequency heating, IR method, far infrared heating, etc. Using one or a combination of heating methods, secondary curing was completed efficiently and in a short time, achieving rationalization, integrated automation, and unmanned production.

[Effect]

According to the above-mentioned means, by making the molding process and the secondary curing process continuous and eliminating the cooling process in the middle,
Since cooling is performed while the physical properties of the resin are stable, residual stress in the plastic package can be significantly reduced, and stress will not be applied to the package when the physical properties of the resin are not stable after molding. This prevents peeling and deformation, which can lead to package cracks and potential defects, resulting in highly reliable semiconductor plastic packages. Furthermore, by using thermoviscoelastic stress analysis simulation, the optimum temperature process and allowable limit temperature process for various resins and packages can be established in a short time. The heating method used in the secondary curing process is a far-infrared heating method with wavelengths that are easily absorbed by plastics (λ = 1 to 20 μm).
), it has a high thermal energy absorption efficiency, accelerates the curing reaction of the resin, and can complete heat curing in a short time. Furthermore, since this heating method uses radiation heating, thermal energy directly penetrates into the resin in the form of electromagnetic waves, and heating and curing proceeds without creating a temperature difference between the inside and the surface layer. Therefore, the package can be completely hardened without causing distortion or stress to the package. By using this heating method in the cooling process and performing radiation cooling, a low-stress, highly reliable package can be realized. Further, by using a plurality of heating methods in combination in the heating method in this secondary curing step, the package can be efficiently heated and reacted using conduction, convection, and radiation heat transfer forms. From the above, it is possible to achieve integrated automation from the molding process to the secondary curing process and rationalization of production, and it is also possible to significantly improve product reliability.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 3 to 6.

Figure 3 shows the result of thermoviscoelastic stress analysis simulation.
The results of an analysis of the relationship between the temperature at which the resin begins to soften, the so-called glass transition temperature Tg, and the residual stress generated at the interface between the lead frame and the resin are shown. in this way,
As the glass transition temperature Tg of the resin increases, residual stress generated at the interface between the lead frame and the resin decreases. For this reason, if cooling is performed in a state where the physical properties of the resin are not stable, that is, in a state where the glass transition temperature Tg is low, a large residual stress will be generated at the interface, which may cause defects such as peeling. Therefore, cooling after molding is abolished, or a cooling process that does not cause defects such as peeling even after cooling is adopted.

As a result of analysis using thermoviscoelastic stress analysis simulation, it was found that the process described below is effective in reducing stress in the package. Next, an example of the process and temperature process will be explained. FIG. 4 shows the current temperature process and the temperature process according to the present invention. The resin used in the analysis is an inorganic filler-filled epoxy resin, which is a phenol-borac type epoxy resin containing 50 to 80 vol% of fused silica filler. The glass transition temperature Tg of this resin is about 135 to 180°C. Further, the semiconductor encapsulating resin is not limited to the above-mentioned epoxy resin, and other encapsulating materials can be similarly applied.

FIG. 4(a) shows the temperature process from the current molding process to the completion of the secondary care process. First, mold temperature Tm1
The product is molded at 60 to 250° C. for a molding time of 30 to 90 seconds, taken out from the mold, and subjected to gate breaking by cooling with a heat transfer coefficient h1 to complete gate breaking, and then stored in a rack. Then, after t1 time has elapsed, again,
So-called secondary curing is performed by hot air heating (heating at temperature T2 for t2 hours) to complete the curing reaction of the sealing resin and stabilize the physical properties, followed by cooling to complete a series of steps to obtain a product.

Figure 4 (b) shows that after molding, heating is continued at the same temperature as the mold temperature, and after the resin reaction has sufficiently progressed (glass transition temperature Tg rises), it is held once near Tg, and then cooled. It is a process. FIGS. 4(c) to 4(e) show examples of heating at a higher temperature after molding.

FIGS. 4(f) and 4(g) show an embodiment of the present invention. That is, FIG. 4(f) shows a step of cooling stepwise after variously changing the heating temperature after molding. FIG. 4(g) shows the step of heating the package again after it has been cooled after molding. Of course, the far-infrared heating method is adopted as the heating method of the present invention. Further, in FIG. 4(g), the resin is cooled once after molding, but in this case, the cooling temperature may be lower than the glass transition temperature (Tg) of the resin. moreover,
With the temperature profile shown in FIG. 4(a), if a far-infrared heating method is used in the heating step (T2, t2) after cooling, the heating time can be significantly shortened.

Figure 5 shows the data for the embodiment of the present invention. Compared to the comparative example (which used the conventional hot air heating method), the embodiment of the present invention, which adopted the far-infrared heating method, took a much shorter time. The glass transition temperature rose at , indicating that the resin curing reaction was fully completed.

Figure 6 shows why the far-infrared heating method is efficient, and is analytical data showing that the far-infrared heater emits electromagnetic waves with a wavelength that matches the absorption wavelength of the epoxy resin.

FIG. 7 is a cross-sectional configuration diagram of a manufacturing apparatus showing an embodiment of the present invention. That is, this device consists of various zones. First, a package 22 molded by a transfer molding machine 21 is taken out from the mold, placed on a conveyance path 24, and is irradiated with far infrared rays from above and below by a heating device 25. . In this step, the curing reaction of the resin progresses and the physical properties become stable. Then, the package 22 heated and irradiated
The materials may be moved along the conveyance path 24, entered the heating storage device 26, and sequentially cooled, and unnecessary materials such as gates may be separated in the next process. Of course, although not shown here, after the package 22 molded by the transfer molding machine 21 is cooled and the gate etc. are separated and stored, the package 2 is heated using the heating device 25.
A step such as heating 2 may be adopted. That is, this method involves the step shown in FIG. 4(a) in which the package is cooled once after being molded, and then heated again with far infrared rays or the like.

When this example is compared with a comparative example (conventional process), significant effects as shown in Table 1 are observed.

In particular, the effect of shortening the processing time from the molding process to completion is remarkable, and if the comparison example is taken as 100%, the processing time can be shortened to about 5%.

〔Effect of the invention〕

According to the present invention, it is possible to optimally control the thermal process applied to the molded product until the completion of the molding process and the secondary curing process, and provide a method for manufacturing semiconductor plastic packages with low residual stress, thereby automating and rationalizing production. , it is also possible to achieve unmanned operation.

[Brief explanation of the drawing]

Fig. 1 is a process diagram for molding a semiconductor plastic package according to an embodiment of the present invention, Fig. 2 is a flowchart of the package manufacturing process, and Fig. 3 is a characteristic diagram of the influence of the glass transition temperature of the resin on residual stress. Figure 4(a)-(e)
is the temperature profile characteristic diagram of the conventional example, Fig. 4(f), (
g) is a temperature profile characteristic diagram of the embodiment of the present invention, No. 5
The figure is an explanatory diagram comparing an embodiment of the present invention with a conventional example, FIG. 6 is a diagram showing the radiation wavelength of far infrared rays and an absorption spectrum of an epoxy resin, and FIG. 7 is a side view of the apparatus of the present invention. 1... Resin tablet, 2... Upper die, 3... Lower die, 4... Pot, 5... Plunger, 6... Runner, 7... Gate, 8... Cavity, 9... Lead frame, 10... Ejection pin,
11... Element, 12... Molded product.

Claims (3)

[Claims] Claim 1: A method for manufacturing a semiconductor plastic package, in which a lead frame with a chip mounted thereon is molded with resin using a molding machine, and after opening the mold, the package is continuously heated by a heating mechanism to fully react and harden the resin. A method for manufacturing a semiconductor plastic package characterized by cooling. 2. In claim 1, the control temperature when transporting the package to the heating mechanism after opening the mold is set to a lower limit temperature at which defects such as interfacial peeling and cracks do not occur in the package, and an upper limit temperature to the temperature at which defects such as interfacial peeling and cracks do not occur in the package. , a method for producing a semiconductor plastic package at a temperature that does not adversely affect the resin or elements. 3. The method of manufacturing a semiconductor plastic package according to claim 1, wherein the package formed by the resin mold is once cooled and the curing reaction of the resin is sufficiently advanced by irradiation with far infrared rays before being taken out.