Delco Electronics Corporation

Hughes Aircraft Company

Petrina L Schnabel

Bruce Alan Myers

Ralph D Hermansen

Henry M Sanftleben

Gary R Shelton

Dennis T Baird

Douglas C Smith

A method is provided for flip-chip bonding a flip chip to a substrate, which may be a ceramic substrate, printed wiring board, flexible circuit, or a silicon substrate, in which a number of input/output solder bumps are reflowed to both bond the flip chip to the circuit board as well as provide the necessary electrical connection between the flip chip and the circuit board's circuitry. The method enables the height of the input/output solder bumps to be closely controlled thereby providing sufficient spacing between the chip and its substrate, thus optimizing the cleanability and stress relief of the package. Generally, the preferred method involves the use of non-input/output, or 'dummy' solder bumps which are present in sufficient numbers to overcome the tendency for the input/output solder bumps to draw the flip chip excessively close to the circuit board. Because the dummy solder bumps are electrically inactive, their height can be governed by electrically isolated pads on the surface of the circuit board. Consequently, definition of the input/output solder bumps and the dummy solder bumps does not require the use of solder stops or masks during formation or reflow of the solder bumps.

Method for controlling solder bump height for flip chip integrated

An acceleration sensor is packaged in an open can and encapsulated in an elastomeric polybutadiene compound which maintains its mechanical properties over a range of -40.degree. C. to 105.degree. C. and transmits acceleration to the sensor with a unity transfer function. The encapsulation material comprises about 90 to 100 pbw of polyol and about 20 pbw of isocyanate, the polyol consisting of at least 70% of hydroxy-polybutadiene. For enhanced adhesion a foaming agent and/or an epoxy is added to the mixture.

Circuit assembly encapsulated with polybutadiene urethane

Growing community of inventors

Kokomo, IN, United States of America

Petrina L Schnabel