07/02/2009, Irvine, California

 

Epoxy Flux Stealing Tacky Flux’s Limelight?

Technology advance has continued to force the development of newer, better performing underfill systems to enhance the reliability of increasingly smaller devices. Manufacturers not only want materials that perform well, but that are also cost-efficient and easily processed. There have been many attempts to satisfy all of these requirements – some successful for certain applications and some not really on the mark.

To date, the four most commonly used types of underfills are capillary flow materials, fluxing (no-flow) underfills, cornerbond and edgebond systems. Each has particular relevance for specific applications, but some new and older-generation devices may benefit from a ground-breaking underfill material technology called epoxy flux. Part of
the class of reflow cured encapsulant materials, epoxy flux is effectively enabling applications for both semiconductor packaging and printed circuit board (PCB) assembly
processes.

In another materials development milestone, Henkel has formulated Hysol FF6000 – a reflow curable epoxy flux formulation that offers both flux and underfill in a single product. The flux component of the material enables solder joint formation and the epoxy system offers underfill-like. Originally designed for underfilling large format CSP and BGA devices where flow rates and cure times of traditional capillary underfills can limit throughput, Hysol FF6000 has also proven to be an effective material for emerging package on package (PoP) configurations as well as for ball attach processes, just to name a few. In addition to its application versatility, Henkel’s new epoxy flux also offers deposition flexibility, as it can be applied via screen printing, dipping, dispensing or jetting.

For PoP assembly, Hysol FF6000 is a promising solution to one of the biggest challenges with these devices. While the level one package assembly follows fairly routine surface-mount procedures, the assembly and subsequent long-term reliability of the level two package is not as simple. Currently, the most common method used is to dip the bottom side spheres of the top package into a tacky flux, place the package and then reflow it. This allows for solder joint formation but, unfortunately, the joints then remain unprotected and are subject to stresses from shock, drop and vibration. Alternatively, when Hysol FF6000 is used, the second level package is assembled using the same procedure but receives some additional support from the adhesive. The second level package is dipped into epoxy flux prior to component placement. Once the component is placed, the assembly moves through reflow where the fluxing action of Hysol FF6000 enables robust solder joint formation and the epoxy component encapsulates each sphere and then cures. In addition to the added protection afforded by this new material, the in-line processing benefits and cost savings are substantial. Units per hour (UPH) is improved dramatically as subsequent dispense and cure steps are not necessary and costs are reduced through yield improvements and the elimination of dedicated dispensing equipment. In recent testing against other tacky fluxes, Hysol FF6000 offered the best drop test performance, as it was able to withstand the most number of drops before the first failure. This suggests that epoxy flux offers more protection than flux alone.

Similar results were revealed when Hysol FF6000 was evaluated as a ball attach flux. Again, the reliability and strength of the material proved to be more robust than that of water-wash or no-clean tacky flux alternatives. When the shear strength of three solder sphere alloys was tested against four different fluxes (two water washable fluxes, one no-clean flux and Hysol FF6000), the Henkel epoxy flux emerged as the clear winner. With each solder alloy, Hysol FF6000 provided the strongest solder joint. These results clearly indicate that higher reliability can be achieved with Hysol FF6000 as compared to traditional flux formulations.

As mentioned previously, the versatility of Hysol FF6000 is unparalleled. From new package configurations such as PoPs to package-level ball attach and, of course, boardlevel assembly of large format BGAs and CSPs, Hysol FF6000 offers manufacturers the ability to source a single material for a variety of applications and deposition methods. This latest material innovation from Henkel also reduces costs, improves throughput and simplifies manufacturing processes while enhancing reliability.

For more information on Hysol FF6000 epoxy flux or any of Henkel’s advanced electronics material solutions, call the company’s headquarters at 949-789-2500 or log onto www.henkel.com/electronics.