A hybrid approach to characterization and life assessment of trilayer assemblies of dissimilar materials under thermal cycles

The  current  study  puts  forward  non-local  closed-form  solutions  for  interfacial  peel  and  shear  stress, as well as warpage deformation, of trilayer structures under thermal cycling. Based on the solution,  a  hybrid  experimental-analytical  inverse  method  (HEAIM)  has  been  proposed  for  characterizing  the  constitutive  behaviour  of  the  trilayer  constituents.  The  method  is  applied  to  optimize  the  correlation  between  the  experimentally  measured  thermal  warpage  of  a  trilayer  structure and the analytically solved warpage.

Furthermore, a localized analytical and experimental method is suggested for characterizing the stress-strain relation of a joint alloy at the interfacial level in the trilayer structure. The resulted viscoelastoplastic model of the joint alloy is further employed in predicting the life of a trilayer structure  that  consists  of  a  failure  dominant  adhesive  layer  made  of  the  same  joint  material.  A  method for  the  thermal  fatigue  life  prediction  is  proposed,  which  applies  critical  plane-energy fatigue damage parameter in combination with a modified Coffin-Manson life model.

The  experimental  evaluation  of  the  proposed  models  and  approaches  for  the  characterization  of  thermally induced trilayer structure deformation and stress, as well as the fatigue life prediction is conducted on several custom-made trilayer structures as well as real microelectronics.  In the study  if  trilayer  structure  reliability  and  durability,  experimental  validation  of  numerical  and  analytical modeling has been rare.  The current study has obtained good agreement between the measured  trilayer  warpage  and  the  predicted  one  using  the  thermomechanical  properties  of  the  trilayer constituents determined by HEAIM, owing to its more accurate prediction for the creep behaviour of the joint alloy. The study of thermal fatigue of the trilayer structure follows a new method  that  involves  the  critical  plane-energy  fatigue  damage  parameter.    The  resulted  fatigue  life prediction has been promising.