Polymer Core Solder Balls Research Articles

Use of Soldered or Glued PCSB as Interconnection between PCB and Ceramic Package in Harsh Environment

Polymer Core Solder Balls (PCSB) have been used as interconnects between a 16 pin leadless chip carrier (LCC) ceramic package and a small FR4 board. A comparison was made between two different volumes of SnPb solder and an isotropic conductive adhesive (ICA) for the attachment of the PCSB to the board and to the package. Shear testing and electrical measurements were performed to characterize the interconnects as bonded and during thermal shock cycling (TSC) tests. No significant reductions of the measured fracture forces was observed for any of the sample groups. However, using a larger volume of solder or ICA resulted in less degradation of interconnect resistance during TSC, and the results for the solder were overall better than for ICA.

Solder Ball Robustness Comparison between SAC 387 and Polymer Solder Balls under AC and TC Reliability Test

Environment and the health concerns due to the hazardous effects of lead resulted in significant activities to find a replacement for lead-contained solders for electronics industrial. Majority of the semiconductor industrial are now replacing lead solders with Tin-Silver-Copper (SAC 387) solder balls. However, dropped balls in SAC 387 for Ball Grid Array (BGA) products due to poor solder joint strength caused by high thermal stress are a major concern in the semiconductor industries. Polymer core inside the solder ball (polymer core/Cu/Sn) is thus integrated to improve the solder ball joint strength. The function of polymer core inside the solder ball is to absorb and released the stress better as compared to the SAC 387 solder ball. Since the diffusion rate of Cu is faster than the diffusion rate of Sn, hence, this could caused the Kirkendall voids tends to form in between the Cu and Sn IMC layer. This would affect the solder ball joint strength and causing drop balls issue. By implement with an extra of Ni layer to the polymer core solder ball (core/Cu/Ni/Sn), could reduce the diffusion from Cu to Sn, thus to overcome the Kirkendall voids and to further improve the solder ball joint strength. This research work studies the performance of the solder ball shear strength of the two types of solder balls applied to MAPBGA device. In this research, both SAC 387 and polymer solder balls were went through under AC (Autoclave) and TC (Temperature Cycle) reliability test up to 144 hours and 1000 cycles, respectively. Solder ball shear strength test was conducted via Dage 4000 series bond tester. From the research work results of the two types of solder balls, the ball shear strength were decreased with an increased of aging and cycles. Overall, it can be concluded that the polymer core solder ball with an additional of Ni layer showed better performance than the polymer core without Ni layer and SAC 387 solder balls, after subjected to the AC and TC reliability test.

A 10 MHz to 80 GHz BGA Transition from Chip to LTCC Interposer for Chip Scale Packages

Presented here are the design, fabrication, and measurement results of a low temperature cofired ceramic (LTCC) chip-to-interposer transition utilizing a flip-chip ball grid array (BGA) interconnect that provides excellent electrical performance up to and including 80 GHz. A test board fabricated in LTCC is used as the interposer substrate and another smaller LTCC part is used as a surrogate chip for demonstration purposes. The BGA chip-to-interposer transition is designed as a back-to-back pair of transitions with an assembly consisting of an LTCC interposer, an LTCC test chip, and a BGA interconnect constructed with 260 μm diameter polymer core solder balls. The LTCC material employed is DuPont™ GreenTape™ 9K7. Full-wave simulation results predict excellent electrical performance from 10 MHz to 80 GHz, with the chip-to-interposer BGA transition having less than 0.5 dB insertion loss at 60 GHz and less than 1 dB insertion loss up to 80 GHz. In an assembled package (back-to-back BGA transitions), the insertion loss was measured to be 1 dB per transition at 60 GHz and less than 2 dB per transition for all frequencies up to 80 GHz.

Comparison study on reliability performance for polymer core solder balls under multiple reflow and HTS stress tests

Drop ball reliability for Ball Grid Array (BGA) package on lead-free product is a major reliability concern. Integrating a polymer core in the solder ball could be a good strategy to dissipate stress better compared to the purely metallic solder ball. However, the diffusion rate of the copper is much faster than the diffusion rate of the solder. Hence, Kirkendall voids starts forming and causing crack between the interface of copper and solder. This could affect the solder joint as well as the solder ball drop reliability especially when subjected to high temperature stress. The new polymer core solder ball with 1μm thickness of nickel (Ni) coated on the copper (polymer core/copper/nickel/solder) could offer better solder ball joint and drop reliability performance. This work studies the effects of IMC growth, solder ball shear strength and drop test reliability. Subsequently, the failure modes were observed after multiple reflow (up to 5 times) and HTS stress tests. The IMC formation was observed under the high power scope with magnification 50× via the mechanical cross-section and was measured using an analytical software tool. Solder ball shear test was carried out to measure the solder joint performance after multiple reflow and HTS stress tests via the Dage 4000 series bond tester. Drop reliability test was carried out via the packing drop test. From this study, we could conclude that the polymer core solder ball with an additional Ni layer coating demonstrates better performance than the polymer core solder ball without Ni layer. The same observation applies to the solder ball shear strength, drop reliability performance in multiple reflow and HTS stress tests. The IMC thickness for polymer core solder ball without additional Ni layer is much thicker than the polymer core solder ball with an additional Ni layer, most probably because Ni could limit the Cu diffusion into the solder, thus resulting in better reliability performance.