Freescale Hones, Demonstrates RCP Technology

One of the most promising developments to emerge in advanced packaging during the past year is Freescale Semiconductor's (Austin, Texas) redistributed chip packaging (RCP) technology — a solution that eliminates wire bonds, package substrates and flip-chip bump interconnects.

The technology quickly garnered industry attention, in part, because it integrates the package as a functional part of the die and system solution, resulting in as much as a 30% reduction in die area and a 30% reduction in thickness, compared with standard molded-array plastic ball grid array (MAPBGA) solutions.

Freescale introduced RCP in July 2006, and has now spent a year honing the technology and demonstrating it in applications ranging from single-die to multiple-chip solutions. “We've further confirmed our reliability and quality studies,” explained Karl Johnson, vice president/senior fellow of Freescale's Wireless & Packaging Systems Laboratory. “We've demonstrated commercial and industrial reliability, and actually pushed some of the technology to moisture sensitivity level [MSL] 1, because we'd ultimately like to qualify the technology for automotive types of applications. We're also continuing to improve the overall process flow, simplifying it to make it more cost-effective.”

The reliability and durability specifications RCP has recently passed include MSL level 3 with 260°C reflow testing, 1500 cycles of air-to-air thermal cycling after preconditioning, and 96 hours of unbiased, highly accelerated stress test (HAST) after preconditioning.

Another area of consideration for RCP development is that as semiconductor technology continues to advance — silicon, in particular — the interaction between the assembly technology of the package and the semiconductor technology is becoming much greater, and the overall performance and reliability is very sensitive to this interaction. “To solve some of these problems, particularly as you shift from 90 to 65 nm and below, the industry is moving to low-k and ultralow-k dielectrics in multilevel stacks, and these materials are not as strong as standard materials and can become brittle,” Johnson said. “Then you run into issues associated with delamination.”

The industry is also currently trying to solve problems related to lead-free solutions and the stresses associated with bonding to these materials. Freescale decided to move RCP in a direction in which they could find a compatible material set that would solve many of the problems with current and future generations. RCP meets RoHS requirements — it is a lead- and halogen-free technology — and is extendable across more than one platform or application.

Since RCP is a chip-first technology that eliminates the substrates that die are mounted to in a standard wire bond of flip-chip BGA, the package is built or integrated around the assembly or die. “The material sets are very compatible with the back end of the silicon process, so they're well matched and the stresses tend to be low. This eliminates some of the issues associated with lead-free bumps in the flip-chip configuration,” Johnson pointed out. “And you can do much higher-density interconnects, because RCP technology uses semiconductor processing rather than a standard substrate type of processing that is generally associated with substrates for wire bond or flip-chip. In general, this has allowed us to shrink the overall package profile size [planar as well as thickness].”

Freescale has also demonstrated embedded components within RCP packages. “It allows us to shrink the overall solution,” Johnson said. “In one of the early radios we built using RCP and package-on-package technology [Figure], we discovered that because of the configuration of the package, the overall parasitics usually associated with assembly were greatly reduced. And there's a lot of flexibility, so this radio we built actually performs better than standard radios using those components on standard PCs and PCBs because of the reduction in parasitics.”

This 25 × 25 mm 3G radio was created using redistributed chip packaging and package-on-package technology. (Source: Freescale Semiconductor)

Right now, the schedule for RCP is that sampling from the pilot line will begin late in the third quarter of 2007. “We'll be doing prototype manufacturing and exercising of the technology through 2008,” Johnson said. “The plan is to have our high-volume manufacturing begin to ramp in 2009.”

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