Thermally conductive dielectrics for insulated metal core cards

Two thermally conductive dielectrics were evaluated for fabrication of double-sided power regulator cards. Both physical and mechanical properties were determined as a function of temperature and fed into a finite element model. Substrate B, a rubber-modified epoxy, exhibited a lower coefficient of thermal expansion (CTE) and higher Tg than substrate A, a cycloaliphatic epoxy dielectric. Substrate A cohesively delaminated following solder shock whereas substrate B exhibited no evidence of cracking. The finite element model correctly predicted the region of highest stress in the cross section of plated through holes of test vehicles built from either substrate.