Underfilled BGAs for a variety of plastic BGA package types and theimpact on board-level reliability

摘要

There are continuous efforts in the electronics industry to reduceelectronic package size. The main force pushing for smaller package sizeis the desire by original equipment manufacturers to reduce their motherboard size and thereby their own cost. Reducing the size of electronicpackages can be achieved by a variety of means and for ball grid array(BGA) packages an effective method is to decrease the pitch between theindividual balls. Reducing the pitch between balls decreases the ballsize and therefore the standoff between the packages and motherboards isreduced. The reduced standoff has the negative effect of reducingboard-level reliability. An experiment to understand board-levelreliability improvement by underfilling the BGA will be presented forseveral fine-pitch plastic BGA types (fleXBGA(R) and MAP (mold arrayprocess)). Four different (snap-cure) underfill epoxies with variedcoefficients of thermal expansion and elastic moduli were used so thatthe preferred set of epoxy properties could be determined. A fullfactorial numerical experiment was used to identify the optimumcombination of CTE and elastic modulus. Results indicate that asignificant increase in board-level reliability can be achieved byunderfilling the BGA