TWI Industrial Member Report Summary 448/1992
M G Murch and S T Riches
Plastics packaging of electronic devices has developed along two main routes: transfer injection moulding has been used for integrated circuit packaging while encapsulating resins have been used mainly to protect chips on circuit board substrates (chip on board) or TAB devices. However, both techniques can give rise to problems in the packaging of advanced electronic devices where increased chip size and reduction in package area may cause problems with device functionality, cracking of the package/resin and failure due to moisture penetration.
A thermoplastic ultrasonic welding technique has potential for encapsulating leadframes and localised lidding of circuit boards where the problems with device and interconnection integrity being affected by contact with the plastics materials encountered in injection mouldings and glob-topping can be avoided. The technique may also be suitable for small batch production where one thermoplastic lid design could be used to encapsulate a variety of components.
This report describes the first ultrasonic welding trials conducted on three thermoplastic materials (polyarylamide, aromatic polyester, liquid crystal polymer and polyphenylene sulphide) to encapsulate Ni-Fe-Co leadframes, and various substrate materials [printed circuit (epoxy/glass FR4 and polyimide)], polyimide tape and thermoplastic substrates (polyetherimide (PEI)).