7/2/2008 9:00:00 AM – Semiconductor International

Flip-Chip Changes on the Horizon
Flip-chips haven’t changed much since being invented by IBM in the early ’60s, but some interesting trends are emerging and several potential changes are on the horizon.
Sally Cole Johnson, Contributing Editor — Semiconductor International, 7/2/2008 9:00:00 AM

Flip-chips haven’t changed much since being invented by IBM (Armonk, N.Y.) in the early ’60s. It’s simply a method of interfacing with an electronic chip. As George Riley, managing director of FlipChips Dot Com (Worcester, Mass.), aptly describes it: The basic flip-chip concept is to take a chip, place conductive bumps on its connection points, flip it over to put it facedown and directly attach it to the circuit. Flip-chips get rid of all excess packaging while also offering benefits, such as high-frequency operation, low parasitics and a high I/O density. They’re used in almost every hot consumer gadget imaginable, ranging from cell phones and pagers to MP3 players and digital cameras.

But some very interesting trends are emerging in the flip-chip arena, with several potential changes on the horizon.

To start with, demand for flip-chips is on the rise thanks, in part, to a spike in gold-bonding wire costs. “Significant trends are taking place because the cost of gold wire is increasing,” explained Raj Pendse, STATS ChipPAC’s (Singapore) vice president of flip-chip and emerging products. “Mobile products or platforms that traditionally used wire bonding, 3-D and stacked die are now an area in which we see future growth potential. A couple of performance reasons are also helping drive a shift to flip-chips: You can miniaturize better with flip-chip, and the silicon used in mobile applications is becoming more dense [higher I/O density]. Rising gold prices have pushed that crossover point to a lower pin count, though. Mobile and handheld applications are typically in the 200-700 pin count range. The crossover point for flip-chip used to be around 1000 I/O, where most of the computing and game consoles are. But now it’s come down to about 500 I/O. From a broad performance and cost perspective, I’m seeing a very big shift into the 200-700 pin count applications — starting with mobile products for cell phones, digital cameras and other handheld products. The way the industry is responding to rising gold costs is to move to copper wire or finer-diameter wire bonding. Or considering making a move from wire bonding to flip-chip instead.”

Demand for flip-chips, such as this flip-chip ball grid array (BGA) system-in-a-package (SiP), is on the rise. (Source: STATS ChipPAC)

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