Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Patent
1992-05-14
1994-08-16
Picard, Leo P.
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
29827, 29841, 437207, H01L 2302
Patent
active
053388992
DESCRIPTION:
BRIEF SUMMARY
This invention relates to methods of packaging electronic devices and to electronic devices when packaged.
A commonly used format for electronic packages is what is known as the "quad flat pack" where the leads which are provided to connect a semiconductor device to the remainder of the system are provided on four sides of the semiconductor device and are formed to a "gull-wing" shape. Once the leads have been formed into this shape, they must be protected from any physical damage while in transit from the package manufacturer to the assembly line.
It is known to seek to protect the leads by the use of a guard ring. With such packages, the guard ring is moulded into the package at the same time as the moulding of a plastic package body around the electronic components. Although such simultaneous moulding of the guard ring and of the package body may be suitable for small sized packages, it is inappropriate for larger sized packages where the volume of material required for large body devices would need expensive machinery and give rise to considerable difficulties in the moulding process.
It is therefore an object of the present invention to provide an improved method of packaging electronic devices, using guard means, which overcomes the aforesaid disadvantages and which can be used with packages of any size.
It is a further object of the present invention to provide a method of packaging electronic devices which can be applied equally to packages of plastics material, ceramic material, or indeed any other material.
In accordance with the present invention there is provided a method of packaging an electronic device encased within a package body and having a leadframe extending therefrom, which comprises securing protective guard means to the leadframe separately from the creation of the package body, said guard means defining a spatial zone within which leads extending from the electronic device are protected.
The guard means is preferably a pre-moulded ring which can be secured to the leadframe either by adhesive or by the use of high frequency vibration.
Also in accordance with the present invention there is provided a packaged electronic device comprising an electronic device encased in a package body, a leadframe extending from the package body, and protective guard means made independently of the package body and secured to the leadframe, said guard means being dimensioned and positioned so that leads extending from the electronic device are protected thereby.
Preferably, the guard means is a continuous element circumferentially around the package body.
BRIEF DESCRIPTION OF THE FIGURES
The Figure is a cross-sectional view of an electronic device and packaging method.
In order that the invention may be more fully understood, one presently preferred embodiment in accordance with the invention will now be described by way of example and with reference to the accompanying drawing which is a schematic cross-sectional view through a packaged electronic device.
As shown in the drawing, a semiconductor device indicated by the broken line 10 is enclosed within a protective package body 11 which may be a moulded plastics material or a ceramic material. Extending from the package body 11 on each of the four sides of the semiconductor device is a leadframe 12. Around the periphery of the leadframe 12 is provided a guard ring 14. The term "ring" is used herein to denote any continuous element extending circumferentially around the package body. It may be circular or rectangular for example. The ring is preferably a pre-moulded component of plastics material. The guard ring 14 may be applied to the leadframe 12 either by the use of an adhesive or, preferably, by the application of high frequency vibration in order to provide local melting of the surface layer of the guard ring. The use of high frequency vibration provides a fast and controlled method of attachment of the guard ring 14 which requires less contamination of the leadframe 12 than the use of an adhesive and which does not impose any extra thermal s
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Horgan Christopher
LSI Logic Corporation
Picard Leo P.
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