Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With contact or lead
Reexamination Certificate
2000-01-06
2003-09-16
Jackson, Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With contact or lead
C257S787000, C257S788000, C257S789000, C257S790000, C257S795000, C257S796000, C257S797000, C438S107000, C156S060000, C156S105000, C156S145000, C156S156000, C156S241000, C156S244210, C156S273300, C156S285000, C156S358000, C156S566000
Reexamination Certificate
active
06621157
ABSTRACT:
The invention relates to a method for encapsulating an electronic component, in particular a semiconductor chip on a substrate. Such methods permit the manufacture of so-called chip scale packages (CSP) with which the completed semiconductor element provided with connection parts is only insignificantly larger than the bare silicon chip.
With this the basic idea lies in that between the substrate and the component there is arranged a buffer mass, for example of a silicone elastomer, which compensates the coefficient of thermal expansion differences of the materials. With this also the soldered connections of the installed semiconductor chip are only subjected to slight stress during environmental temperature fluctuations. The life duration and reliability of such chip scale packages is thus relatively high. Known manufacturing methods are for example described in “Semiconductor International”, November 1997, page 48, or in U.S. Pat. No. 5,659,952 or U.S. Pat. No. 5,679,977. In spite of the improved properties of the end product, the known methods are however relatively complicated and do not permit an efficient manufacture. In particular there are necessary numerous individual steps with a comparatively high cost with respect to required apparatus and time required for manufacture. It is therefore an object of the invention to provide a method of the above mentioned type with which fewer processing steps are required. Furthermore with the placing of the component onto mechanical installation parts and/or onto the component itself there is to be effected no unnecessary exposure to heat because micromechanical processes with a simultaneous heat effect are difficult to handle and may tend to degrade the electronic component.
This object according to the invention is achieved with a method in which the buffer material and/or an adhesive in a liquid or pasty (flowable form is deposited from a dispenser onto a substrate. With this at least one working step which was necessary until now may be saved, specifically the pressing on of an adhesive in a stencil printing method. The component itself is at room temperature placed onto the buffer material and/or onto the adhesive and not as previously in the heated condition. With this the term “room temperature” is to be understood as a temperature which prevails in working rooms corresponding to the applicable standards in air conditioning technology and which settle roughly in the temperature range from 10° C. to 45° C., preferably from 16° C. to 26° C. With this the throughput per unit of time is improved since no heating time for the component is required. Mechanical installation parts and/or measuring instruments are not compromised by the effect of heat.
After the placing-on of the component the buffer material and/or the adhesive may be subjected to a precuring and a curing and specifically advantageously on the same installation as the placing-on of the component. By way of this in a particularly advantageous manner there is exploited the condition that with the adhesives applied here, the joining together of the parts to be connected and the curing of the adhesive do not necessarily have to coincide. By way of the temporal separation, the precuring and/or the curing may be effected in an installation region at which heat development is less problematic. After the precuring or curing the connected units without risk of a mutual displacement of the substrate and component may be transported to any other working station.
An essential process simplification may be achieved in that firstly several buffer cams or nubbins are applied to a substrate such as in a stencil printing method, the buffer cams are cured. Before the placing-on of the component, adhesive is deposited with the dispenser on or next to various buffer cams. With this method existing stencil printers for depositing the buffer cams (nubbins) may be used. In contrast the despositing of the adhesive is effected in a considerably more simple manner with the dispenser. Advantageously adhesive is deposited simultaneously from several dispenser openings, each to one of a plurality of nubbins. Under certain circumstances a dispenser, which in rapid succession coats a group of buffer cams with an adhesive would however also be conceivable.
With a suitable material choice the dispenser may be used to deposit the buffer cams may be deposited onto the substrate and be secured thereto. Subsequently each buffer cam may be provided with an adhesive layer. This may either be effected with a separate dispenser or with the same dispenser.
A further essential simplification of the process may finally be achieved in that an adhesive material may be applied that simultaneously serves as a buffer material. With this the subdividing into two separate materials is done away with, which simplifies the procedure as a whole. The adhesive may with this be deposited in the form of individual buffer bodies, which remain alone after the placing-on of the component. Subsequently, the voids are together with the covering of the wiring locations, filled out with a protective mass. Alternatively however it is also conceivable that the adhesive, with the dispenser, is deposited as an adhesive pattern which after placing on the component connects to a homogeneous layer between the component and the substrate. Air pockets are thus prevented and a retrospective filling out of the voids is no longer necessary. Such adhesive patterns are already known in semiconductor encapsulation technology.
Further advantages may be achieved when the depositing of the buffer material and/or of the adhesive, with the dispenser, is effected directly shortly before the placing on of the component at the same machine. Advantageously with this also the substrate, on the same transport system, is led past the dispenser and the placing-on device for the component. On the one hand with this both working steps may be exactly matched to one another and the drying or curing time may be better controlled. In the same machine and on the same transport system a smooth transport is possible, by which means the danger of an inadvertent displacement of the component from the nominal position is greatly reduced. Before the placing on the component is advantageously adjusted with respect to position.
An improvement of the planarity of the component and the substrate may be achieved in that during the placing on of the component the substrate is secured on a rest surface by way of a vacuum.
For improving the manufacturing rationality advantageously groups of components are fastened on the same substrate. For this in each case several components after one another are deposited to a group. The whole group may then simultaneously be subjected to a pressing-on pressure and/or to a heat treatment. This pressing on and/or heating in groups may also be applied with alternative encapsulation processes in which the components are not deposited at room temperature. The simultaneous processing of the components may be effected via commonly actuated individual tools, such as e.g. individual pressing punches, which however are actuated simultaneously. Alternatively it may also however be the case of a common tool which impinges the whole group simultaneously, such as e.g. a common pressing punch of a suitable size.
Generally, in order to ensure an adequate adhesion and to cure the elastomer mass, the components with the simultaneous heating must be pressed against the substrate.
A disadvantage of the known method lies however in the fact that the exact placing of the components on the substrate and the final connection under a high pressure and at a high temperature is effected in one step. The pressing procedure with this lasts considerably longer that the placing procedure which leads to great capacity reductions in the production line. On the other hand however the application of high temperatures in the region of the placing of the components is disturbing in that the heat may damage the component or the adhesive materials. At the placing station, spec
Herbst Wolfgang
Ritzmann Heinz
Wirz Gustav
Alphasem AG
Jackson Jerome
Ortiz Edgardo
Shoemaker and Mattare
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