Vertical Interconnection Using PCB Interposer With Double-side Solder Bumps

Board level system integration is a three-dimensional assembly technologydevelopment direction and research content, the accompanying study of scientific issuesis a very meaningful topic.The structure of adapter plate for bonding between the plates was designed for thefirst time in the research. We identified the surface treatment process of the adapterplate pad and the solder structure, and then analyzed the influence of laser reflow timeon solder bumps on the morphology and shear strength. Then using different solderbump structures prepared different adapter plates to analyze the interfacial reactionprocess of laser remelting and the influence of different laser remelting time on thesolder bumps interface and internal organization. The double-side bump adapter platethat we made can completed the bond between plates by hot air remelting and properalignment and control. Finally we analyzed the internal organization changes of convexpoints after the bonding process.The results showed that: the proper laser remelting parameters can manufacturetransfer board solder bumps of good quality, different solder and different surfacetreatment processes bonding pad showed different shear strength, but higher than theshear strength of hot air remelted solder bumps, the reason is that the laser remeltedsolder bumps is more superior on tissue density uniform, toughness and anti-fatigueperformance. Analysis on the interface reaction mechanism, diffusion and dissolution ofbonding pad metal elements is the physical basis of solder bumps preparation by laserremelting. Dissolution rate of different bonding pad element in the molten solder isnot the same, Au fastest, Cu followed, Ni is the slowest.Therefore the form andthickness of the intermetallic compounds on the interface is different in the process oflaser remelting. Due to the faster heating and cooling rates of laser remelting, the grainsize and orientation of solder bumps are also different from that of hot air remelting. Inthe experiment, we found that SAC solder bumps grain number of the laser remelting ismore than that of hot air remelting of solder bumps, but no certain preferred orientation.Different solders generate different interface types and forms of intermetalliccompounds under different time of laser remelting. It might because the balances underdifferent thermodynamic conditions are different.We completed the bond between plates using double-side bump adapter plate thatmade by laser remelting, and made a three-dimensional assembly samples. It means that solder bumps made by laser remelting experience hot remelting process again afterplates bonded. We analyzed its evolution process, grain coarsening, convex pointprecipitating metal compounds inside and that SAC solder bumps that composed bymultiple grains transformed into a single large grain. Form of interface compoundscomposition has also changed, hot air leveling Cu pad on all converted to stable Cu6Sn5phase, the reaction of ENIG bonding pad is more complicated, the interface is transferedform Ni3Sn4phase to (Cu,Ni)6Sn5, precipitation(Cu,Ni)3Sn and Ag3Sn phase.