At The ConFab conference in Las Vegas in June, Mike Ma, VP of Corporate R&D at Siliconware (SPIL), announced a new business model for interposer based SiP’s, namely the “turnkey OSAT model.” In his presentation “The expanding Role of OSATS in the Era of System Integration,” Ma looked at the obstacles to 2.5/3D implementation and came up with the conclusion that cost is still a significant deterrent to all segments.

By Dr. Phil Garrou, Contributing Editor

Over the past few years, TSMC has been proposing a turnkey foundry model which has met with significant resistance from their IC customers. Under the foundry turnkey model, the foundry handles all operations including chip fabrication, interposer fabrication, assembly and test. Foundry rivals UMC and GlobalFoundries, have been supporting an OSAT/Foundry collaboration model where the foundries would fabricate the chips with TSV and the OSATs would do assembly of chips and interposers that could come from several different sources.

FIGURE 1. Amkor’s “possum” stacking technology.

SPIL is the first OSAT to propose this OSAT centric model where the interposer is fabricated by the OSAT who then assembles and tests modules made with chips from multiple sources. The impediment to this route in the past has been the lack of OSAT capability to fabricate the fine pitch interposers which require dual damascene processing capability, which until now was only available in the foundries. This week SPIL announced the equipment for fine pitch interposer capability (>2 layers, 0.4-3µm metal line width and 0.5µm TSV) has been purchased and is in place.

Ma indicates that while the foundries are not happy with this SPIL proposal, their customers, especially their fabless customers have been very supportive. He feels the inherent lower cost structure of OSATS will have a positive impact on the 2.5/3D market which has been somewhat stagnant since the FPGA and memory product announcements in 2010.

Also presenting at The ConFab: Bob Lanzone, Senior VP of Engineering Solutions for Amkor. He, like the other OSATS, sees smartphones and tablets driving the market moving forward.

Amkor’s update on Copper Pillar technology indicates an expected doubling in demand this year and continued expansion into “all flip chip products”. Their “TSV status” takes credit for being the first into production with TSMC and Xilinx.

Looking at the 2.5D TSV and interposer supply chain they see different requirements for high end, mid-range and lower cost products. For high end, such as networking and servers, silicon interposers are needed with < 2µm L/S, 25k μbumps per die. Amkor is engaged with foundries to deliver silicon interposers today.

For mid-range products, such as gaming, graphics, HDTV, and tablets, silicon or Glass interposers are need with < 3µm L/S, < 25ns latency and ~10k μbumps/die. Amkor is not actively pursuing glass interposers yet as the infrastructure is still immature.

For lower cost products, such as lower end tablets and smart phones, silicon, glass or laminate interposers are needed, with < 8um L/S, low resistance and ~2k μbumps per die. Lazone said a cost reduction path must be provided to enable this sector, and they are working with the laminate supply chain to do that. They are targeting 2014 for their “possum” stacking as shown in FIGURE 1. •