A Reliable Method for Direct Chip Attach for Mixed Technology Integration

The emergence of compact products employing mixed technologies, such as personal digital assistants, wireless communicators and sensor systems, is creating a host of new needs in electronics packaging. These products are driven by small size, light weight, high-operating frequencies, unique micro-to-macro interfacing and low-cost. There is a need for a simplified and reliable process for direct chip attachment. Through under-filling the chip with a solid encapsulant, direct chip attach technology is now a reliable method for attachment of small chips to polymeric substrates. The encapsulant redistributes stress in the package from the fatigue-intolerant solder joints. However, the encapsulant's effect is to force the chip and the substrate to take up the strain, bulging the substrate and the chip. This bulging causes its own new set of problems such as making larger chips susceptible to cracking during bending. Another problem is that the degree of bulging, and hence the degree of strain relief, is highly dependent on the flexibility of the structure of the underlying substrate. For MEMs, this bulging will have significant impact on the performance of the device attached. The objective of this proposal is to demonstrate a new, reliable, compliant direct chip structure that eliminates this bulging. A program to improve direct chip attachment technology is of the highest priority for industry. The realization of this technology will reduce the cost and increase the reliability of a myriad of military and commercial products that require high-density, chip-scale packaging. The improved cost and reliability will impact a broad range of applications with an annual market potential for the technology exceeding $50 million.