GB2127736A

GB2127736A - Molding apparatus

Info

Publication number: GB2127736A
Application number: GB8321044A
Authority: GB
Inventors: Kazuo Bandoh
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-08-09
Filing date: 1983-08-04
Publication date: 1984-04-18
Also published as: DE3328408A1; JPS5926244U; GB8321044D0; DE3328408C2; JPS6233317Y2; GB2127736B

Abstract

A molding apparatus for sealing semiconductor chips in a resin, comprising a fixed upper mold section (106) and a movable lower mold section (113) which are opposed to each other. The movable lower mold section (113) is formed with a plurality of pots (114) extending therethrough, each pot having a plunger (115) intimately fitted therein from below at all times. The plungers (115) are adapted to be moved upwardly by cylinders (116) attached to a lower mold clamping platen (108), whereby the molding material pressed by the plungers is forced into the individual cavities under the same conditions only via culls and gates. <IMAGE>

Description

SPECIFICATION Molding apparatus for sealing semiconductor chips in resin This invention relates to a molding apparatus, suitable for sealing semiconductor chips in resin, and more particularly is concerned with transfer molding apparatus.

The construction and operation of transfer molds is well known and is described, for example, in Chapter 7 of Plastics Mold Engineering Handbook, Third Edition, edited by J. Harry DuBois and Wayne I. Pribble, and published in 1978 by Van Nostrand Reinhold Company. One such known transfer mold is described below with reference to Figure 1 of the accompanying drawings.

This apparatus comprises a fixed platen 2 attached to the upper end of a frame 1, a fixed upper mold section 6 attached to the under side of said platen through a heat insulating plate 3, spacer block 4 and a plate 5, a movable mold clamping platen 8 adapted to be vertically moved by a hydraulic cylinder mechanism 7 installed in the lower region of the frame 1, and a movable lower mold section 13 attached to the upper side of said mold clamping platen 8 through a heat insulating plate 9, a plate 10, a spacer block 11, and a plate 12.

The central portion of the upper mold section 6 is provided with a single vertically extending cylindricaj pot 14 of large size, into which will be charged a molding material in the form of a thermosetting synthetic resin, such as silicone resin or epoxy resin. Disposed above the fixed plate 2 is a transfer cylinder 16 equipped with a plunger 15 fitted in said pot 14 for pressing the molding material. A space 17 is defined in a region above the pot by said spacer block 4, the said space facilitating the charging of material into the pot.

The molding surface of the upper mold section 6 is formed with a plurality of cavities for forming the upper halves of molding, while the molding surface of the lower mold section 13 is formed with a cull 19 in opposed relation to the pot 14 associated with the upper mold section, and is also formed with cavities 20 in opposed relation to the cavities 1 8 of the upper mold section for forming the lower halves of the moldings.

The cull communicates with said cavities 18 and 20 through runners 21, which are passages for the molten molding material, and gates 22 connecting said runners to the cavities 20 of the lower mold section.

This conventional apparatus further comprises, in the illustrated disposition, a space 23, ejector pins 24 and 25, ejector plates 26 and 27, a spring 28, a return pin 29, an ejector pin 30, a push-up pin 31, a push-down spring 32, a throughgoing hole 33, an ejector bar 34, a return pin 35, a guide pin 36, a guide bushing 37, and a heater 43 for the plunger 15.

When semiconductor elements are to be sealed in resin by molding using the conventional apparatus arranged as outlined above, with the upper and lower mold section 6 and 13 heated to the required temperature in advance, a plurality of lead frames having semiconductor elements attached thereto are placed in position between the mold sections and the mold is closed, whereupon the required amount of molding resin material is charged into the pot 14 through the charging space 17.Subsequently, the plunger 15 is inserted from above into the pot 14 to press the molding material, whereupon said material is melted under heat from the mold sections 6 and 13 and pressure from the plunger 15, the molten resin then being forced into the upper and lower cavities 18 and 20 through the cull 19, runners 21 and gates 22, so that the semiconductor elements on the lead frames in said cavities are sealed in resin by molding.

Upon completion of sealing in resin by molding, the mold is opened and the moldings 39 are pushed out of the upper and lower cavities 18 and 29 by the upper and lower ejector pins 24 and 25.

The ejected moldings 39, having the semiconductor elements sealed therein in the molded part containing the lead frames 38 are integrally connected together by a cured resin portion 40 which remained in the cull 19, cured resin portion 41 which remained in the runner 21, and the cured resin portions 42 which remained in the gates 22, as shown in Fig. 5(1) and (II). Thus, according to the aforesaid conventional apparatus, the amount of the cured residual resin which is unnecessary is inevitably large, bringing about a drawback that the percentage utilization of molding material is considerably low.

In the positional relation between the cull 1 9 and the upper and lower cavities 18 and 19, when the states of resin molding in the cavities which are close to the cull 1 9 and in the cavities which are remote from the cull 19 are compared, it will be seen that the viscosity of the resin being injected into the individual cavities differs from cavity to cavity owing to the fact that the curing reaction of the resin is accelerated while the molten resin is transferred along the runners, with the result that, in the case of the cavities located remote from the cull 1 9, the viscosity of the resin being forced into these cavities through the gates 20 is relatively high, and hence the amount of resin injected into the cavities is insufficient, tending to produce defective moldings.

Further, in the aforesaid conventional apparatus, since the pot 14 is located at the upper mold section 6, it is necessary to install a high transfer cylinder 16 above the fixed platen 2, thereby considerably increasing the overall height of the apparatus so that the operation of installing the apparatus or moving it to another site of installation cannot be carried out smoothly and easily. This drawback is serious because, depending upon the circumstances attending the site of installation of the apparatus, the drawback makes it necessary to remove the transfer cylinder 1 6, and it is extremely difficult to restore the required accuracy in reassembling the cylinder.

According to the present invention there is provided a molding apparatus, suitable for sealing semiconductor chips in resin, comprising a first, fixed mold section, a second, movable mold section opposed to said first, mold section, a plurality of molding material filling channels extending through said movable mold section, each channel being provided with a respective plunger and a number of transfer cylinders each of which is attached to clamp means associated with the second mold section so as to move said plungers, said channels communicating with cavities in the first and second sections only through culls and gates.

According to one embodiment of the present invention a molding apparatus suitable for sealing semiconductor chips in resin, comprises a fixed upper mold section, a movable lower mold section opposed to said upper mold section, a plurality of molding material charging pots extending through said movable lower mold section, plungers fitted from below in the respective pots at all times and a required number of transfer cylinders attached to a movable mold clamping platen so as to vertically upwardly and downwardly move said plungers, each of said pots communicating with cavities in the upper and lower mold sections only through culls and gates.

According to the aforesaid embodiment of molding apparatus of the invention, since each of the pots of the apparatus communicates with the cavities only through culls and gates without having to provide runners, the flow passage of molten resin is greatly reduced in length, thus greatly reducing the amount of the residual cured resin which becomes unnecessary after molding, increasing the percentage utilization of molding material, thereby saving materials.

Further, since the distances between the individual pots and the associated cavities are equal, the conditions for pressurized injection of molten resin into the cavities to seal the semiconductor chips therein can be maintained uniform to provide molten parts of resin which are excellent and uniform in quality.

Furthermore, the arrangement wherein the pots are formed in the lower mold section, the plungers are fitted from below in the pots at all times, and the transfer cylinders for vertically upwardly and downwardly moving the plungers are attached to the movable clamping platen, provides the following advantages.

There is no need for a special provision of a molding resin charging space which has been indispensable to the conventional apparatus, nor is there the need for upwardly withdrawing the plungers from the pots in charging the molding material into the pots. As a result, the overall height of the apparatus can be reduced by the corresponding amount, so that even if the lintel of the entrance or the ceiling of the room for installation of the apparatus is low, the apparatus can be easily set in position or can be moved from place to place. Thus, the aforesaid serious drawback of the conventional apparatus can be eliminated.

Since the plungers are heated at the same time as the mold is heated, the heaters for exclusive use with the plungers, which have been indispensable to the conventional apparatus, are no longer necessary. Further, the particular arrangement of the invention makes it possible to greatly reduce the distance over which the plungers are moved, and to employ reduced sized transfer cylinders, thereby making it possible to attain a reduction in the size, and in particular the height, of the apparatus and in installation cost.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which Fig. 1 is a front view, partly in section, of a conventional molding apparatus; Figs. 2 through 4 show a preferred embodiment of a molding apparatus of the present invention; Fig. 2 is a front view partly in section: Fig. 3 is a front view, partly in section, showing said apparatus in the mold opening state as well as in the molding injection state; Fig. 4 is a perspective view, partly in longitudinal section, of the principal portions of the upper and lower mold sections:: Fig. 5(1) and (II) is a front view and a plan view of residual resin remaining with a molded part as produced by the conventional apparatus shown in Fig. and Fig. 6(1) and (oil) is a front view and a plan view of residual resin remaining with a molded part as produced by the apparatus of the present invention.

An embodiment of a molding apparatus for sealing semiconductor chips in resin according to the present invention will now be described with reference to Figs. 2 through 4, and Fig. 6.

The molding apparatus of the invention is comprised of a fixed upper mold 106 disposed below a platen 102 attached to the upper end of a frame 101, and a lower movable mold section 113 disposed above a movable mold clamping platen 108 adapted to be moved up and down by a lifting mechanism 107 including a hydraulic cylinder disposed in the lower region of the frame 101.

The fixed upper mold section 106 is attached to the lower side of the fixed platen 102 through a heat insulating plate (not shown), a spacer block 104, and a plate 105, whereas the movable lower mold section 113 is attached to the upper side of the movable mold clamping platen 108 through a heat insulating plate 109, a spacer block 111, and a plate 112. Respectively disposed in a space 144 defined by the spacer block 104 and a space 123 defined by the spacer block 111 are ejector plates 126 and 127 provided with ejector pins 124 and 125, respectively, for releasing moldings of resin formed in cavities 118 and 120 in the upper and lower mold sections.Associated with the upper ejector plate 126 are a push-up spring 145 for said plate, a return pin 129 for pushing down the lower ejector plate 127 upon mold clamping, and an ejector pin 130 for releasing cured resin remaining in a cull 119. The spring 145 serves to pull up the ejector pins 124 and 1 30 upon mold clamping, until their lower ends are flush with the bottom surfaces of the cavities 11 8 and 11 9. The fixed platen 102 is provided with an ejector mechanism 146 comprising a hydraulic cylinder for pushing down the ejector pins 124. Thus, when the piston rod 147 of said ejector mechanism is lowered, the ejector plate 126 is forced to descend against the force of said spring 145.

Further, the ejector plate 127 is provided with a return pin 135 in opposed relation to the return pin 129 of the ejector plate 126. The lower surface of the ejector plate 127 is provided with springs 148 for pushing up said plate when the mold is opened, said springs being downwardly compressed by the ejector plate 127 adapted to be lowered by the return pin 129 abutting against the return pin 129 when the mold is clamped. At this time, the upper ends of the ejector pins 125 are lowered until said ends are flush with the bottom surfaces of the cavities 120 in the lower mold section. Disposed between the plates 105 and 112 are a guide pin 136 and a guide bushing 1 37, which cooperate with each other to position the mold when the latter is clamped.

At predetermined positions on the movable lower mold section 113 disposed in opposed relation to the fixed upper mold section 126, there is a plurality of molding material charging pots 114 which extend through said lower mold section. Molding material pressing plungers 115 are fitted from below in the respective pots at all times. Each of said pots 114 communicates with the associated cavities 11 8 and 1 20 of the upper and lower mold sections through the associated culls 119 and gates 122.

The back surface of the movable mold clamping platen 108 is provided with the required number of small transfer cylinders 11 6 for moving said plungers 11 5 up and down. Further, as schemically shown in Fig. 3, at one side of the apparatus, a pallet 1 50, for automatically taking out molded parts released from the mold, is arranged so that it can be automatically advanced and retracted in a horizontal direction between the upper and lower mold sections when the mold is opened.

The process for sealing semiconductor chips in resin by molding by the use of the apparatus arranged in the manner described above will now be described.

First, the mold comprising the mold sections 106 and 113 heated to the required temperature is opened. Then, lead frames having semiconductor elements attached thereto are set in position between the mold sections, and a molding material in the form of a thermosetting resin, such as epoxy resin, is charged at the parting line (P.L.) into the pots, whereupon the mold is clamped.

Subsequently, the plungers 115 are upwardly moved to press the molding material into the pots 114, whereupon the molding material is melted under heat from the mold sections 106 and 11 3, and pressure from the plungers 11 5. The molten resin is forced into the cavities 118 and 120 via the culls 119 and gates 122, so that the semiconductor elements disposed on the lead frames placed in the cavities are sealed in resin by molding.

When the mold is opened, the ejector pins 125 are upwardly moved by the springs 148 as the lower mold section 113 is moved, whereby the moldings of resin are upwardly pushed out of the cavities 120 and gates 122, and are thereby released from the mold. At this time, since the ejector plate 126 associated with the fixed mold section 106 remains lifted by the spring 145, the moldings of resin remain in place in the cavities 118 and culls 119 in the upper mold section.

In the above condition, as shown in Fig. 3, the pallet 150 is automatically advanced to be positioned under the upper mold section 106, whereupon the ejector mechanism 146 is actuated to lower its piston rod 147, with the result that the ejector plate 126 is pushed down against the force of the spring 145, thus causing the ejector pins 124 and 130 to release the moldings from the mold and drop them onto the pallet 150, whereupon the latter is automatically retracted away from the mold. Thus, the molded part is automatically taken out.

The molded part 149 taken out in this manner, as shown in Fig. 6(1) and (II), has lead frames 138, resin moldings 139 having semiconductor elements sealed therein, and cured resin portions 140 and 142 which remained in the culls 119 and gates 122. Thus, of said molded part 149, the residual cured resin portions 140 and 142 become a loss, but the total amount of loss is very small because it does not exceed the residual amount of resin in the culls 119 and gates 122.

Further, since the molten resin to be transferred from the pots to the cavities is injected under the same conditions only via the culls 119 and gates 122, molded resin parts of uniform quality can be obtained.

In addition, although not shown in the drawing, the transfer cylinder 11 6 can as well be mounted on the upper surface of the movable mold closing platen, and furthermore, the transfer cylinder 11 6 can be provided with either balancing springs or a balancing manifold to exert an upward pressure upon each of the plungers 11 5.

Claims

1. A molding apparatus, suitable for sealing semiconductor chips in resin, comprising a first, fixed mold section, a second, movable mold section opposed to said first, mold section, a plurality of molding material filling channels extending through said movable mold section, each channel being provided with a respective plunger and a number of transfer cylinders each of which is attached to clamp means associated with the second mold section so as to move said plungers, said channels communicating with cavities in the first and second mold sections only through culls and gates.

2. A molding apparatus as claimed in claim 1, wherein, when the apparatus is in use, the first mold section is disposed above the second mold section, and the plungers are moved in upwardly and downwardly extending directions.

3. A molding apparatus for sealing semiconductor chips in resin as claimed in claim 2, wherein a fixed platen disposed above in order to attach the upper mold section is provided with means for ejecting the molded parts.

4. A molding apparatus for sealing semiconductor chips in resin as claimed in claim 1 or 2, wherein a pallet for taking out molded parts is installed in such a manner that it can be advanced and retracted between the first and second mold sections.

5. A molding apparatus substantially as hereinbefore described with reference to and as shown in Figures 2 to 6 of the accompanying drawings.