A multi chip module (MCM) is a semiconductor package that includes bare semiconductor dice. Typically, the multi chip module includes an interconnect substrate for mounting and interconnecting the dice, and a housing for sealing and protecting the dice. The interconnect substrate can include contact members that establish electrical communication with bond pads or other contact locations on the dice. In addition, the interconnect substrate can include interconnect circuitry that provides an electrical path to the contact members and to input/output terminals for the module.
One contact technology that is utilized to establish electrical communication between the contact members on the interconnect substrate and the bond pads on the dice, is known as "flip chip bonding". With flip chip bonding, the dice are formed with raised bond pads having solder bumps. For forming a multi chip module, the dice are mounted face down to the interconnect substrate and the solder bumps are bonded to corresponding contact members on the interconnect substrate. Typically for flip chip bonding, the contact members on the interconnect substrate are flat metal pads.
One shortcoming of flip chip bonding is that the solder bumps and contact members on the substrate must have a minimum size and pitch to accommodate formation of a reliable electrical connection. In general, the dimensions of the bumps and contact members must be oversized to accommodate misalignment between the dice and substrate. Because of this requirement, the module must be formed with a relatively large surface area. Also the density of the dice can be limited by the large number of bond pads required by some dice.
In addition to density limitations, a temperature differential can develop between the dice and the interconnect substrate due to heat generated during operation of the integrated circuits formed on the dice. Since the solder bumps are constrained in the x, y and z directions, stress fractures can develop as a result of the temperature differential. The stress fractures can cause an unreliable electrical connection between the dice and substrate and can cause the mechanical bond between the dice and substrate to loosen.
Because of density and alignment limitations, alternate methods have been developed for forming multi chip modules. One prior art method of forming multi chip modules that does not utilize flip chip bonding is disclosed in U.S. Pat. No. 5,189,505 to Bartelink. This method includes forming contact members on the substrate comprising a post and a flexible membrane. Conductors formed on the substrate have one of their ends supported by the posts. Identical contact members are formed on the dice and can be bonded to the contact members on the substrate with a solder ball. This arrangement allows the posts and conductors to flex to accommodate misalignment between the substrate and dice. In general, this type of contact member is relatively complicated and requires an expensive and complex manufacturing procedure.
In view of the foregoing, a need exists for improved methods for constructing multi chip modules. In particular, a module is needed in which alignment can be effected between the dice and interconnect substrate even with a dense array of dice having a large number of closely spaced bond pads. In addition, the module must be able to accommodate a temperature differential between the dice and interconnect substrate without detriment to the electrical and mechanical connection therebetween.
USPTO Backgrounds
USPTO Backgrounds