NOVEL TRANSFER MOLDING TECHNIQUE FOR ENCAPSULATING PBGA PACKAGES
Author: Ron Molnar Company: Abpac Inc. Date Published: 1/25/2000
Pan Pacific Symposium
Abstract: An automold press has been recently developed to interface to an automated material handling system and to transfer mold plastic Ball Grid Array (BGA) discrete substrates. The program objectives were: (1) to mold in a Class 10K clean room, (2) to mold discrete substrates transported in flat plate carriers, (3) to avoid any known patent issues with BGA molding, (4) to mechanically and electronically integrate the mold press to an ESEC Autoline®, and (5) to meet standard industry requirements for environmental reliability and mechanical dimensions. The benefits of assembling discrete substrates over strip-based substrates are discussed. These include significant substrate material cost savings, flexibility to assemble different substrate materials, and standardization on a single carrier size. Moldability and reliability results from a study of five transfer molding compounds received from three suppliers are presented. Three different packages were evaluated – a 2-layer 13 x 13 mm CSP, a 2-layer 27 x 27 mm PBGA, and a 4-layer 35 x 35 mm PBGA. The CSP was molded as a 4-up, 35 x 35 mm array and subsequently sawn to size. The CSP had a thinner mold cap than the PBGAs. All of the test vehicles were assembled with organic BT substrates. The reliability test conditions are described. Pressure cooker test was the most discriminating test for evaluating reliability differences between the various mold compounds. One of the five compounds showed superior reliability performance for both PBGA and CSP packages. In fact, it exceeded the JEDEC Level 2 moisture sensitivity requirements. Results of molding new package constructions, including multichip modules with passive components, PBGA+™ and thin 1.2 mm CSP, are described. X-ray photos, and scanning acoustic micrographs illustrate the moldability of these new packages.