Stencil Printing Techniques for Challenging Heterogeneous Assembly Applications: Parts 1 & 2
Authors: Mark Whitmore, Jeff Schake Company: ASM Assembly Systems Date Published: 9/17/2017
Abstract: The challenges associated with stencil printing of miniaturized components in heterogeneous assembly are well documented with proven printing solutions . Now with the reality that the ultra-small Metric 0201 passive component is being introduced to market, printing capability is once again not assured. In Part 1 of this study, a series of focused Metric 0201 experiments investigating printing process sensitivity to circuit board properties, including pad dimensional accuracy and landscape topography, identified stencil gasket as significantly important on achieving print process control. The effects of pad size influencing print quality were found to be less using a nano-coated stencil. The print quality produced on undersized Cu pads was significantly degraded with an un-coated stencil, whereas full Cu pads printed better. A stencil with an applied nanocoating improved print volume uniformity on all Cu pad sizes more significantly than improving overall paste transfer efficiency. Based on testing, the recommended print process used an 80?m thick nano-coated foil, which outperformed a 50?m thick stepped stencil of equivalent aperture size. Subsequently, in Part 2 of the study full assembly trials were conducted with optimized print process parameters. Heterogeneous assembly was successfully observed but concerns over excessive solder joint volumes have been raised.
Heterogeneous, 0201, 008004, passive, fine pitch, stencil printing, nano-coating, miniaturization.