Patent Application
20090067139
This invention relates to electronic assemblies having a large electronic component mounted to a circuit board, and more particularly to electronic assemblies subjected to a vibration environment.
Large electronic components having electrical leads soldered to a circuit substrate are vulnerable to damage when subjected to repeated shock and/or vibration which cause relative movement of the large electronic components with respect to the circuit substrate. Such movement places stresses on the solder joints. These stresses can eventually result in failure of the electrical connection. Without some means of dampening the effects of shock and/or vibration, unsatisfactorily high failure rates could occur for certain types of electronic assemblies used in environments in which the electronic assemblies are exposed to substantial shock and vibration, especially repeated and frequent shock and/or vibration. For example, electronic assemblies used in certain automotive applications, such as engine control units (ECUs) and engine control modules (ECMs) are typically provided with dampening means for reducing the deleterious effects of shock and vibration.
One technique for preventing damage and failure due to shock and/or vibration of an electronic assembly having a large electronic component soldered to a circuit substrate is to adhesively bond a surface of the electronic component to a housing or case for the assembly. This solution is not entirely satisfactory because adhesive materials have a coefficient of thermal expansion that is substantially different from the coefficient of thermal expansion of the body of the electronic component and substantially different from the coefficient of thermal expansion of the housing or other component to which the electronic component is adhesively bonded. These differences in coefficients of thermal expansion will cause the adhesive to expand and contract in response to temperature changes in a manner that is different from that of the other components of the assembly. More specifically, the adhesive will tend to expand and contract at a different rate than the body of the electronic component and the body of the housing or other assembly component to which the body of the electronic component is adhered. These differences in the rates of expansion of the different materials will induce relative movement of the body of the electronic component with respect to the circuit substrate creating stresses on the solder joints. The stresses on the solder joints can result in cracking of the solder joints and failure of the electronic assembly. In addition, most adhesives tend to shrink during cure because of physical changes to the adhesive material, or contract after cooling down from the cure oven. These changes in geometry, can also cause stresses on solder joints and result in failure of the electronic assembly.
Another technique for preventing damage and failure due to shock and/or vibration of an electronic assembly having a large electronic component soldered to a circuit substrate is to retain the large electronic component between opposite end plates welded or otherwise fixed to the body of the large electronic component and to the circuit substrate. However, the shock and/or vibration can often be sufficiently severe to cause the weld or other fixation to become broken, resulting in failure of the electronic assembly.
The invention provides an improved electronic assembly in which an elastic dampening member and a clamping arrangement are utilized to stabilize an electronic component against lateral movement without imposing any substantial stresses on the solder joints.
In accordance with an aspect of the invention, an electronic assembly includes a circuit substrate, an electronic component, an elastic dampening member, and a clamping member that compresses the dampening member between the clamping member and the electronic component. In accordance with this aspect of the invention, the dampening member has a top section engaging an upper surface of the electronic component and opposite end walls that extend downwardly from the top section of the dampening member and engage opposite sidewalls of the body of the electronic component. Further, in accordance with this aspect of the invention the clamping member urges the opposite end walls of the dampening member against the opposite sidewalls of the electronic component.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Shown in
In the illustrated embodiment, body 16 of electronic component 14 is also secured to circuit substrate 12 with supporting end plates 22 which are welded to opposite sidewalls 24 at weld joints 26 (as shown in
A rigid clamping member 38 forcefully engages an upper surface of the opposite end walls 36, and thereby urges lower ends 40 of end walls 36 of dampening member 30 against the sidewalls 24 of the body 16 of electronic component 14. This can be accomplished for example by having the upper surfaces 42 of dampening member 30 atop end walls 36 sloped slightly toward each other (i.e., sloped toward top section 32).
In the illustrated embodiment of
In the electronic assembly shown in
In
Details of dampening member 56 are illustrated in
The circuit substrates which may be employed with the invention encompass generally any printed circuit board or wiring board on which conductive traces may be defined and on which electronic components may be mounted or formed.
The dampening members employed in the invention are elastic in the sense that they are relatively resiliently deformable as compared with the relatively more rigid clamping members or housing members. The elastic dampening members may comprise an elastomer (e.g., an elastic polymer), such as natural rubber, polyisoprene, butyl rubber, halogenated butyl rubbers, polybutadiene, styrene-butadiene rubber, nitrile rubber, hydrated nitrile rubber, chloroprene rubber, ethylene-propylene (EPM) rubber, ethylene-propylene-diene (EPDM) rubber, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber, fluoroelastomers, perfluoroelastomers, polyether block amides, tetrafluoroethylene/propylene rubbers, chlorosulfonated polyethylene, ethylene-vinyl acetate, thermoplastic elastomers, thermoplastic vulcanizates, polyurethane rubber, polysulfide rubber, and the like.
As shown in
It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.
