NCP Technology Paves the Way for Integrated, Advanced Packages
Underfills have been part of the electronics landscape for decades, offering protection for numerous devices inside a variety of electronic products.
Different types of applications – everything from automotive to smart phones to computers – use various package designs such as PoPs, BGAs and stacked packages, whereby all of the electronic interconnects are protected by some sort of underfill material.
In the late ‘90’s and early in the 21st Century, the majority of high performance logic devices like FPGAs, QFPs, SiPs and QFNs used and still use architectures which rely on wirebonding to form the device interconnections. As greater functionality and miniaturization drivers persist, however, the trend is quickly moving toward higher I/O counts, package integration, and greater performance and flexibility. For these reasons, many new package designs are using flip chip as the preferred and more high-density interconnect method. What’s more, as logic and memory begin to converge, 3D integrated packages using through-silicon vias (TSVs) will become more prevalent.
Flip chip designs are also numerous, with some incorporating gold stud bumps, some using stacked bumps, gold plated studs or copper pillars with solder caps. As devices become smaller, thinner and stacked, we will see the emergence of micro-bumps with TSV. Unlike wirebonded packages, flip chip packages use underfill for protection of the interconnected bumps. Traditional capillary underfills (CUF), however, can present some challenges with narrow gap and fine pitch flip chip devices, which is why many packaging specialists are turning to non-conductive pastes (NCPs) as a viable and more streamlined alternative. The chart below shows a comparison between the NCP process and the standard CUF technique. As is evident from the diagram below, using NCP eliminates several steps as compared to CUF, effectively shortening the underfill process by as many as three process stages and also reducing materials costs due to the elimination of fluxing and cleaning. In addition, NCP is pre-applied onto the substrate, thus interconnection and bump protection are achieved in a single step. This is the key advantage of NCP since CUF is applied after bump formation. That’s not to say CUF doesn’t have its advantages; it does. It is a higher UPH process than NCP method, but that is its primary benefit as compared to NCP.
Using copper (Cu) pillar technology as a means of evaluation, we can compare NCP versus CUF processes. For gap filling with fine-pitches of less than 50 µm and gaps less than 25µm, NCP completely fills the spaces. With CUF, it is likely that a vacuum or pressure-assisted process may be required to pull the underfill and fill the gaps without any voids. Form factors also benefit from NCP use, as the material fillet can be controlled. When using CUF, the fillet is generally wider so limits the potential to place two chips side by side. There are multiple other advantages, all which are outlined in the table below.
Understanding the market dynamics and the growth of flip chip packages, Henkel has developed a suite of NCP materials to address flip chip underfill requirements. These include HYSOL FP5000, HYSOL FP5001, HYSOL FP5200 and, the most recent material, HYSOL FP5201. Designed for compatibility with both gold bumps and copper pillar technology, HYSOL FP5201 enables production of modern, finer-pitched flip chip designs. Other benefits of HYSOL FP5201 include its fast cure in less than five seconds using wide bonding temperature range, with no voiding, excellent electrical performance and its outstanding reliability performance of MSL3, thermal cycling testing up to 1,000 hours, HAST testing up to 96 hours and proven performance when tested for 1,000 hours of temperature storage and temperature/humidity exposure.
NCP technology is most certainly enabling next-generation flip chip devices that are currently limited by wirebonding techniques and traditional capillary underfill materials. And, Henkel is advancing NCP technology with novel state-of-the-art technologies that are compatible with smaller form factors and ultra-fine pitches, again reconfirming the company’s innovation leadership position.
For more information on Henkel’s HYSOL FP5201 or any of its advanced NCP products, log onto www.henkel.com/electronics or call 714-368-8000.