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Samsung piles chips for thin MCPs

Posted: 01 Jan 2007 ?? ?Print Version ?Bookmark and Share

Keywords:multichip packages? MCPs? NAND flash? multimedia mobile phones? MP3 players?

Samsung SSD caching solution 'eliminates delays' in Windows Vista PCs" target=_blank>Samsung Electronics Co. is touting an advanced packaging technology that piles 16 chips on top of each other but maintains a heightif one could call it thatof only 1.4mm. There isn't any immediate demand for packages with that many stacked chips, but Samsung researchers believe that the methodology may be applied to slim down today's conventional multichip packages (MCPs) a bit.

Samsung, the top NAND flash producer, stacked 16 flash chips to attain a single-package density of 16Gbytes. In the future, the stacked chips could be ideal for memory-hungry consumer electronics systems, such as multimedia cellphones or MP3 players. It's possible to mix and match the types of chips in the package, but because it's harder to stack chips similar in size, Samsung stuck with NAND to prove out the concept, said Pyoung-Wan Kim, an engineer with the interconnect product engineering team at Samsung Electronics' semiconductor business.

Currently, five-chip stacked packages are the limit in commercial applications. Most of those are used in cellphones, but they are generating interest in smaller gadgets, such as MP3 players.

Samsung's accomplishment builds on work it did in 2005, when the company revealed a 10-chip MCP that was 1.6mm thick. One of the challenges at that time was thinning the adhesive between the chips from 60?m to 20?m and ensuring stress reliability.

This time around, Samsung researchers also moved to a single-wire contact rather than two. Instead of running wires from both sides of the chip, only one side is used for contacts, with the die stacked off-center, in a zigzag pattern, to save space and shorten the wire connections. To allow for single contacts, engineers changed the design of the redistribution layer that had been added to the wafer so that there was only one pad contact and not two.

Although adding more chips to the package won't substantially increase the height, Samsung engineers are still looking at ways to refine the technology. "Our future challenges will be in researching new ways to bring thinner adhesives or moldings to the package," Kim said.

Thin gets thinner as Samsung stacks 16 chips within a 1.4mm profile.

In the end, Samsung thinned its wafers to 30?m to achieve its goal, or about 65 percent of the thickness of wafers used in its 10-die MCP. In total, about 95 percent of the original wafer was thinned away. Samsung engineers then used lasers to slice up the delicate wafers, which were too thin for the traditional wafer saws used to cut wafers around 80?m thick.

- Mike Clendenin
EE Times

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