Flip-chip fine package and its assembly line development for GaAs MCM

A newly developed flip-chip fine package (FFP) and its assembly line are presented in this paper. The FFP offers outstanding features such as small size, low profile, low cost, high reliability, low thermal resistance and ease of use, and is suitable for GaAs MMICs used in cellular phones because they require smaller and lighter packages. The developed GaAs MCM FFP has a pin count of 16 with 0.5 mm pitch and package size of 2.5×2.5×0.5 mm in which two GaAs MMICs are flip chip bonded. Ink is directly printed on the exposed backside of a GaAs chip. A 0.25 mm thick Al₂O₃ ceramic substrate with 59×91 mm area and W-Ni-Au interconnection is used as an array substrate containing 360 pieces of 2.5×2.5 FFP. Au-Au ultrasonic flip chip bonding techniques are applied to connect GaAs chips via 15 μm high Au bumps on bonding pads to the ceramic substrate. This technique has the advantages of reducing bonding temperature, force and time. Use of a ceramic array substrate and the ultrasonic technique is the key to achieving low cost. Some new machines and software are prepared for FFP fabrication. The underfill machine can handle very small quantities of liquid resin. With new software, dicing direction is automatically adjusted to the cutting line, after detecting the substrate shrinkage errors occurred during high temperature co-firing. After dicing, each MCM FFP is picked up, tested and put into the emboss-tape continuously by a machine. Reflow test with JEDEC level-1 -65°C-150°C temperature cycle test and PCT showed no failure. This result means FFP is as reliable as conventional resin mold packages