Ball grid array having reduced mechanical stress
AssigneeIndustrial Technology Research Institute
InventorTony H. Ho
Life of this patent
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Abstract
A semiconductor package, including semiconductor dies, a ball grid array, and a printed circuit board, is described. Said package has been designed with a view to minimizing its level of internal mechanical stress. This has been achieved through use of two sets of solder joints that have different melting points. The joints with the higher melting point are positioned in the region, on the ball grid array, where it is known that stress will be a maximum in the finished package. The lower melting point joints occupy the remaining positions on the underside of the ball grid array. Ball grid array and printed circuit board are attached to one another by heating at a temperature that is between the aforementioned two melting points.
Claims22
A semiconductor packaging structure comprising:
- an electrically insulating .mechanically stressed substrate having a top surface and a bottom surface;
- a region of maximum mechanical stress within said substrate;
- a semiconductor die mounted on said top surface;
- means, located on said top surface, for electrically contacting selected areas on said die;
- a first plurality of solder joints, integral with said bottom surface and projecting downwardly therefrom, positioned so as to underlie said region of maximum mechanical stress;
- a second plurality of solder joints, integral with said bottom surface and projecting downwardly therefrom, having a lower melting point than said first plurality of solder joints and arranged as a regular array over said bottom surface, excepting locations occupied by said first plurality of solder joints;
- and
- wiring layers, embedded within said substrate between said top and bottom surfaces, for connecting said means for contacting the die to the solder joints.
A method for forming a semiconductor package comprising:
- providing at least one semiconductor die;
- providing a ball grid array that includes a first and a second plurality of solder joints, said first plurality having a higher melting point than said second plurality;
- attaching said semiconductor die to said ball grid array;
- determining the region within said ball grid array where mechanical stress will be at a maximum once said semiconductor package has been fully assembled;
- positioning said first plurality of solder joints within said region of maximum stress;
- positioning said second plurality of solder joints as a uniform array on said ball grid array, excepting the positions occupied by said first plurality;
- providing a printed circuit board;
- and
- attaching said ball grid array to said printed circuit board by heating the package to a temperature that is above the melting point of said second plurality of solder joints and below the melting point of said first first plurality of solder joints.
Dependencies are inferred from the claim text.