KR19980086768A - Apparatus and method for molding plastic packages - Google Patents

Abstract

The present invention includes an upper mold, a cavity plate, and a lower mold for encapsulating and sealing various BGA packages using a transfer molding process. The upper mold has a network of runners for connecting with one or more spruces. The cavity plate has one or more cavities on the side facing the lower mold for forming the mold with respect to the substrate sandwiched therebetween when clamped. At the side of the cavity plate facing the upper mold, one or more conical channels are arranged for receiving the resin from the runner. The tip of the conical channel extends to a submarine gate placed in the center of the cavity to push the resin inwards with minimal wire sweep. The combination of the runner's network and the conical channel reliably and economically encapsulates the BGA package in various matrices.

Description

Apparatus and method for molding plastic packages

The present invention relates to an apparatus and a method for molding a plastic package for a semiconductor. In particular, the present invention relates to an apparatus and method for reliably and economically molding a ball grid array (BGA) package.

BGA packages are intended to overcome the limitations of conventional packages such as quad flat packs (QFPs) in terms of cost, power dissipation, speed and input / output (I / O) pin count. Critical to this is the ability of the electronics industry to reliably and economically mold BGA packages using existing surface mount technology and equipment. In general, BGA packages are smaller and thinner than packages with the same equipment speed and I / O pin counts according to the prior art. When the BGA package is suitable for higher speeds and I / O pin count applications, phenomena such as wire sweeping are not a big problem in conventional package technology.

In addition, there is a continuing trend to create tightly coupled systems such as multi-chip modules (MCMs). MCM is a package that has one or more chips inside and combines more than one hundred high-performance silicon ICs with substrate structures designed for the application. The electronics industry assembles standard single-chip modules on printed wiring boards (PCBs) at high productivity and low cost, so BGA packages typically work with MCMs. Nevertheless, the common practice of using MCM's glove top encapsulation process is to reduce the productivity and economics of surface mount technology.

It is an object of the present invention to reliably encapsulate a BGA package.

Another object of the present invention is to reliably and economically encapsulate an MCM BGA package.

The present invention has an upper mold, a cavity plate and a lower mold to encapsulate various BGA packages using a transfer molding process. The upper mold is characterized in that it comprises a network of runners in communication with one or more spruces. The cavity plate has one or more cavities on the side facing the lower mold for forming the mold with respect to the substrate sandwiched between when clamped. At the side of the cavity plate facing the upper mold, one or more conical channels are arranged for receiving the resin from the runner. The tip of the conical channel extends to a submarine gate positioned at the center of the cavity to receive resin therein while minimizing wire sweep. The combination of runner network and conical channel economically and reliably houses the BGA package in a variety of matrices.

1A is a cross-sectional view of a cavity down type ball grid array (BGA) package with molded or encapsulated resin in dotted lines;

FIG. 1B is a cross-sectional view of a BGA package of the cavity up type with overmolded resin shown in dashed lines. FIG.

2 shows a gate plate molding method for sealing a plastic package in a capsule according to the prior art.

3 shows a detachable hollow plate molding method for sealing a plastic package in a capsule according to another prior art.

4 shows a globbing method for filling molding resin for plastic packages according to another prior art.

FIG. 5 is a diagram showing the warpage of the matrix BGA substrate according to the molding globbing method, and it is practically impossible to adjust the substrate to a suitable die size.

6 is a top elevation view according to the present invention in which a BGA matrix substrate is molded using a conical channel system and a single runner to achieve better results.

FIG. 7 is a cross sectional view of a structure according to the present invention, seen along the line A-A of FIG. 6;

* Explanation of symbols for main parts of the drawings

1,11 ... BGA Package 2 ... Chip

4 ... heat sink 6,16 ... substrate

8 ... soldering board 12 ... IC

21 ... cavity 22,32 ... gate

51,59 ... mold base 52 ... plunger

53 ... upper mold 54 ... spruce

55 ... cavity plate 57 ... lower mold

An apparatus and method for encapsulating a BGA package is described. In the following description, spurs, runners and mold plates and the like will be described in detail so that the present invention can be fully understood. Those skilled in the art will be able to practice the invention without detailed description. Known parts necessary for the heating and movement of the resin as well as the clamping operation of the transfer mold are not shown for clarity of the present invention.

1A and 1B show simplified cross-sectional views of two representative structures of a BGA package. In FIG. 1A, the BGA package is shown in a cavity down structure. The scope of a typical BGA package is described in US Pat. No. 5,583,378. The BGA package 1 consists of an integrated chip (IC) 2 attached to a heat sink 4. In FIG. 1A, the state in which the chip 2 is coupled to the substrate 6 is not shown in detail. Those skilled in the art should understand that the chip is wired to the substrate or connected by TAB. A solder bowl 8 is attached to the bottom of the BGA package 1. The area between the dashed line and the chip 2 represents the volume 10 encapsulated with the resin and is of interest to the present invention. The industry applies to dams and chip encapsulation processes that protect chips. First, rectangular dams are selectively placed around the die using highly viscous capsules. The rotary pump then spirally fills the dam with low viscosity capsules. See, for example, the CAM / ALOT liquid distribution system.

In FIG. 1B, the BGA package 11 is shown in a joint up structure. The package 11 includes an IC 12 attached to the top surface of the substrate 16, and the solder bowl 18 is attached to the bottom surface of the substrate 16. As with the BGA package shown in FIG. 1A, the method by which the IC is coupled to the substrate has been omitted. Volume 20 represents the encapsulation resin. The package 11 illustrates a broad plastic BGA structure pioneered by Motorola Citizen, which has been termed an over mold plastic pad array carrier.

2-4 illustrate a molding method according to the prior art used to encapsulate plastic BGA structures. In Figure 2, a gate plate molding method for encapsulating a plastic package is shown. The package 20 is molded transversely with the gate 22 connected to the cavity 21. This approach is described in detail in US Pat. No. 4,442,056 published by Dusan Slepcevic. In FIG. 3, the detachable cavity plate 30 comprising one or more cavities 21 and transverse gates 32 follows the method described in US Pat. No. 4,332,537 published by Dusan Slepcevic to encapsulate a plastic package. . Finally, Figure 4 highlights the most common method of encapsulating a BGA package, namely the glove upper encapsulation method. For example, referring to FIG. 6 of US Pat. No. 5,355,283 published by Marrs et al., The glove top encapsulation method fills a BGA die by dispensing epoxy in each layer to allow bubbles to move inside the resin.

Known methods of encapsulating plastic packages have many limitations that cannot be easily solved with existing surface mount technologies and equipment. First, transverse introduction of the capsule into the cavity often results in wire sweeps in BGA packages with high I / O pin counts. Second, in MCMs with poorly standard test procedures, the electrical problems caused by wire sweep can further worsen the reliability of advanced BGA packages. Third, the glove upper encapsulation approach has the problem of long time consumption and quality control. The process of encapsulating a BGA matrix substrate using the glove top encapsulation method is shown in FIG. 5, where the warpage 42 of the substrate can occur abruptly because the thermal expansion coefficients of the substrate and capsule are different. This makes it difficult to control the substrate with each BGA die.

6 and 7 are top and side views of a structure according to the invention for encapsulating a plastic package. The present invention combines the know-how of transfer molding for gang-pot molds as well as separable cavity plate molding techniques. Those skilled in the art will appreciate that injection molding and transfer molding are distinguished for the use of thermosetting resins or capsules within transfer moldings for encapsulating semiconductor devices. In contrast, injection molding equipment is suitable for operating with thermoplastics. In Figures 6 and 7, the present invention 50 includes a lower mold 57, a detachable cavity plate 55 and an upper mold 53 for securing a substrate 66 incorporating a matrix of plastic packages comprising a BGA structure. It characterized by including). Those skilled in the art will understand that the upper mold base 51 and the lower mold base 59 are necessary to work with the present invention. The mold bases 51 and 59 have a function of maintaining the heat generated by the pot to heat the resin pellets or strips.

In FIG. 6, the upper mold 53 according to the invention has at least one spruce 54 at the bottom to receive and redirect the heated resin compressed by the plunger 52. For the substrate 66 comprising the matrix of the BGA package 60, a composite plunger or gang-port mold according to the invention 50 is recommended. In a preferred embodiment of the invention, the spruce 54 is coupled to the network of runners 56 with respect to the center of the BGA package. Runner 56 helps the resin to move easily into each cavity under the upper mold. Since the runners 56 are interconnected, the flow of resin in the runners is balanced.

In FIG. 7, a cross-sectional view of the detachable cavity plate 55 sandwiched between the upper mold 53 and the lower mold 57 is shown. At least one conical channel 58 is disposed on the surface that is flush with the upper mold 53 and faces the upper mold to receive the resin exiting the runner. The narrow end of the conical channel 58 extends to the submarine gate through one or more cavities 60 for the BGA package. In FIG. 7, the substrate 66 is fixed between the cavity plate 55 and the lower mold 57. The location of the conical channel relative to the cavity is one of the features of the present invention: receiving the resin from the center of the cavity rather than the side ensures that the flow of resin in the cavity is uniform. The resin flows in the same direction as the fan in wire bonds or TAB leads. As such, the probability of occurrence of wire sweep is significantly reduced. In addition, problems associated with the movement of highly viscous resins in the cavity are also minimized. In general, the present invention gives the electronics industry all the advantages of transfer molding technology without the drawbacks associated with conventional cavity molding or plate molding.

The encapsulation process of the BGA substrate is as follows. In FIG. 7 the plunger 52 moves upward in the port 62 and pushes the heated resin into the spruce 54 and enters the cavity 60 through the runner 56 and the conical channel 58. When plunger 52 senses back pressure generated from the network of runners, this indicates that the resin has completely filled the cavity. The clamping process according to the invention is terminated when the appropriate curing time for the capsule has elapsed. The structure of the removable cavity plate 55 makes it easy to separate the runner from the cavity, reducing the encapsulation cycle of the BGA substrate.

Although Figures 6 and 7 illustrate the encapsulation of a matrix BGA substrate, the present invention can easily encapsulate an MCM BGA substrate suitable for various applications where the arrangement of the BGA structures may be irregular. Therefore, the present invention can be modified for various kinds of substrates.

Although the present invention has been described with reference to FIGS. 1 to 7 with an emphasis on an apparatus and method for encapsulating a plastic package weighted on a BGA package, it should be understood that the drawings are illustrative only and not limited thereto. The method and apparatus of the present invention are also used in many application areas where a package of semiconductor devices is required. Those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope of the invention as described. For example, the present invention can be applied directly to other substrates such as ceramics, TABs, and the like.

Claims (2)

At least one runner system and at least one runner system for transferring resin from the at least one plunger and port assembly, including a spurs, a lower mold for supporting a substrate comprising at least one plastic package, a lower mold and an upper mold for receiving resin from the runner system A cavity plate sandwiched between the cavity plates having at least one conical channel on a surface facing the upper mold, the channel encapsulating the plastic package in communication with the at least one cavity for encapsulating the substrate, the system comprising: A system, characterized in that the substrate is reliably sealed in a capsule while minimizing problems such as wire sweeping in a plastic package. The encapsulation system of claim 1, wherein the cavity plate extends to a tip having a submarine gate.