SINGAPORE -- Halogen-free compounds might be "greener," but researchers are finding their metallurgical effects leave a lot to be desired.

According to a paper published at the Electronics Packaging Technology Conference in Singapore last week, so-called "green mold" compounds used in place of halogen flame retardants in plastic packages are often characterized by quartz filler, sometimes at levels topping 85%.

High quartz levels lower the CTE, in some cases by more than half versus traditional mold compounds. The subsequent mismatch in thermal expansion between the package and printed circuit board is causing solder joint fatigue cracking, researchers found. The investigators are calling this failure mode "Cu lead fatigue fracture."

Other issues stem from the higher elastic modulus of the quartz-filled alternatives, which leads to more package stress.

For their study, the researchers investigated two types of TSOPs.

The paper was "Green Mold Compounds: Impact on Second Level Interconnect Reliability," authored by Bart VanDevelde, Melina Lofrano and Geert Willems of IMEC.