Don’t Forget Thermal Profiles for Adhesives

With the push to Pb-free soldering there is an increased focus on profiling for solder pastes. Many people in assembly realize the importance of using this critical measurement when defining and monitoring a process.

What is often not known is the importance of profiling for adhesive curing. Looking at a typical data sheet for an underfill, surface mount adhesive, potting material, etc. — there are recommended cure conditions. This is the recommended cure time and temp for the adhesive in order to obtain optimum properties (the ones listed on the datasheet). This means the adhesive itself needs to see this time and temperature.

For example, an underfill has a recommended cure of 5 minutes at 150°C. This underfill is placed under a metal-lidded BGA on a 0.092” thick board (that contains a power plane and a ground plane) and then placed in an oven with 20 to 30 other boards of the same configuration, set at 150°C for 5 minutes. To the surprise of the manufacturer the underfill did not appear to have cured.

Subsequent to this, a profile was taken of the area under the components found that the underfill was attaining only up to 130°C as a peak. Using a standard profiler, we found that once loaded the boards needed to remain in the oven for 15 minutes in order for the underfill to attain 150°C for 5 minutes.

Therefore, it is important to perform thermal profiling for adhesives as well as for solder pastes in order to produce reliable parts.

This entry was posted in Sticky Notes by Brian. Bookmark the permalink.

About Brian

Brian J. Toleno, Ph.D. is the Application Engineering Team Leader with Henkel in Irvine, California. He holds a Ph.D. in analytical chemistry from Penn State University and a B.S. in chemistry from Ursinus College. Prior to joining Henkel, Toleno managed the failure analysis laboratory at the Electronics Manufacturing Productivity Facility (EMPF). He is an active member of SMTA, served as the Program Chair for the 2005 IEMT and is active within the IPC, serving as the underfill handbook committee (J-STD-030) chairperson and co-chair of the Solder Paste Standards Committee (J-STD-005). Toleno has written a course on failure analysis for SMTA, has authored numerous publications for trade journals and peer reviewed publications, and written two chapters for electronic engineering handbooks on adhesives and materials.