07/23/2012, Irvine, CA

 

Underfill gets Tight New Formula Ideal for TMV PoPs

When package-on-package (PoP) devices emerged on the scene a few short years ago, they presented many challenges to assembly specialists. Not the least of these hurdles was how to ensure reliable protection of the top level package interconnects, as underfilling the space between the two packages presented some obstacles.

The narrow gap between the packages can sometimes slow the flow of underfill so much that air can be trapped in this space as the underfill flows around the outer bumps. These challenges have been largely overcome and PoPs are arguably the preferred technique for 3D memory integration. And, like most useful devices, PoP architectures have continued to evolve, again presenting some device protection challenges.

There’s a new PoP design on the scene:  through mold via (TMV) PoPs. Similar to traditional PoPs, TMV PoPs have been widely adopted by manufacturers of handheld devices, as they deliver the ability to pack more functionality into a tighter space. With these packages, however, the gap between the bottom package mold cap and the underside of the top package is extremely narrow and, therefore, much more difficult to effectively underfill. In fact, with some TMV PoP designs, the gap height can be as small as 10µm. Clearly, this narrow a space requires an underfill with excellent flow characteristics to ensure complete coverage in a relatively short amount of time while maintaining good reliability.

To ensure reliability and address the underfill flow requirements needed for robust TMV PoP assembly, the materials experts at Henkel used its market-leading ECCOBOND 1216 underfill material as the foundation for a novel formulation specifically for tight gap TMV PoPs, as well as for fine-pitch BGAs, CSPs and WLCSPs. The new material, LOCTITE ECCOBOND E1216M, is a non-reworkable underfill with outstanding flow performance and reliability equal or better to its predecessor. In fact, this underfill flows twice as fast as the previous version so, for devices with very narrow pitch and gaps, the faster flow characteristics speed up processing time and ensure more complete coverage. 

In terms of reliability, LOCTITE ECCOBOND E1216M offers superior performance. In over 1,000 hours of -40°C to 85°C thermal cycling testing on a 0.4mm CSP test vehicle, the material had zero failures. Drop testing was equally as impressive with 100 drops before the first failure and no underfill failures. The material is snap-curable, provides fast and void-free underfilling of area array devices, has excellent adhesion and strength and is a non-anhydride curing chemistry. Added to all of these advantages is the long, three-day work life of LOCTITE ECCOBOND E1216M, which reduces material waste and provides excellent manufacturing flexibility. 

There’s no doubt that package architecture will continue to undergo dynamic changes as the industry strives to add function and reduce product size. And, as our indispensable handheld devices become increasingly value-packed, protecting the internal components is more critical than ever before. Underfill technology such as LOCTITE ECCOBOND E1216M is making modern convenience and connectivity possible.

For more information on LOCTITE ECCOBOND E1216M or any of Henkel’s innovative underfill materials, log onto www.henkel.com/electronics, e-mail electronics@henkel.com  or call 1-888-943-6535 in the Americas, +44 1442 278 000 in Europe and +86 21 3898 4800 in Asia.