Wafer-Level Packaging With Soldered Stress-Engineered Micro-Springs

Abstract

Micro-springs for integrated circuit test and packaging are demonstrated as soldered flip chip interconnects in a direct die to printed circuit board package. The spring interconnects are fabricated with thin film metallization as the last step in a wafer-scale process. The z-compliance of the interconnects can be used to test and/or burn-in parts in wafer form. After the parts are diced from the wafer, the springs then become the first-level (and often the last-level) interconnect between the chip and the board. The xy-compliance of the interconnect enables considerably large die to be soldered to an organic printed circuit board without underfill using a surface mount compatible process. To demonstrate this concept, daisy chain test vehicles were fabricated on die measuring 11.5 mm 6.5 mm with 48 spring contacts on a 0.8 mm 0.65 mm grid array, each spring measuring 400 m 100 m. The parts were placed onto organic boards with screen printed solder paste using a pick and place machine. The parts were reflowed to complete the solder connection to each spring using eutectic and lead-free solder. Assembled parts have undergone 20 000 hot plate thermal cycles and 1000 oven thermal cycles without failure.

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“…[14][15][16][17][18][19] Such MEMS microcoils are applied to coil springs used for providing appropriate contact forces in fine electrode probe pins of semiconductor device testers with large-scale integration (LSI). [20][21][22][23][24][25] However, because LSI devices are aggressively integrated and refined further, electrode pitches are expected to be shortened corresponding to device integration and miniaturization. Accordingly, the tester probe pin pitches have to be decreased.…”

“…For this reason, various types of minute contact probes have been proposed. [26][27][28][29][30][31] Contact probe pins with built-in coil springs are advantageous for shortening the pin pitch two dimensionally in comparison with microprobes supported by cantilevers because the probe pins with built-in coil springs need small spaces for support. However, the microcoil springs built in the probe pins should be downsized further to make the probe-pin diameter drastically smaller.…”

A package demonstration with solder free compliant flexible interconnects

“…Electronic packaging based on stress-engineered spring interconnects [3,12] can potentially improve chip testing, rework, and mechanical compliance. With conventional flipchip bonding, the rigid solder reflown microbumps can cause package failure due to excessive shear, as there is a significant CTE mismatch between a silicon integrated circuit (IC) die and the package substrate.…”

“…In previous work we have demonstrated high density gold-gold pressure contacts at 6μm for a laser bar array [4], and at 20 μm pitch for an LCD driver chip [12]. Soldered springs have also been demonstrated for chip to board applications such as memory [3]. The fabrication approach has also been used to build high quality factor coils [5], large angle MEMS actuators [6], and tall tip atomic force microscopy tips [7].…”

“…As die sizes, I/O count, and power densities grow, significant challenges develop in connecting chips to their first-level packages. Additionally, ongoing developments in 3D integration and multi-chip modules (MCMs) present new opportunities for novel I/O technologies that improve performance despite severe dimensional constraints.Electronic packaging based on stress-engineered spring interconnects [3,12] can potentially improve chip testing, rework, and mechanical compliance. With conventional flipchip bonding, the rigid solder reflown microbumps can cause package failure due to excessive shear, as there is a significant CTE mismatch between a silicon integrated circuit (IC) die and the package substrate.…”