While harsh environment testing requirements have continued to increase, there have also been broader trends of advancing electronics density, voltage, and miniaturization. Ensuring end product reliability necessitates taking all of these changes into account throughout processing. As a solder manufacturer, Indium Corporation has seen how the automotive electronics’ trend toward harsher test conditions has required a few relatively major changes to the solder paste material itself.
The conditions outlined by the International Electronics Manufacturing Initiative (iNEMI) as “Elevated harsh” or the even greater “Severe harsh” have caused a shift away from standard SAC alloys towards those that are generally considered “high-reliability alloys” for specific applications. Thermal cycling tests from -40 to +150 °C replicate extreme operating conditions and ensure good performance therein. Despite efforts to make high-reliability alloys “drop-in” solutions, it is important to remember that these alloys are metallurgically complex. They enable enhanced thermal cycling performance, although the alloy is not the only variable in the equation. Thermal cycling can also be impacted by other factors, including the flux vehicle, component type, surface finish, and processing conditions among others.
Miniaturization of high impact
A fact that can occasionally be lost in the excitement of drastic innovation is that there are changes that do not necessarily increase performance requirements, but steadily increase the challenges of reaching existing quality and reliability standards. Miniaturization is a trend that revitalizes “old” necessities related to printing and processing. The impact of miniaturization is relevant across many applications due to a shared increase in expectations for electronics. The expanded everyday use of electronics and its integration into lives, homes, and vehicles operation and, in turn, are driven by miniaturization. Familiar metrics can continue to be used– such as area ratio, print transfer efficiency, and standard deviation– for these soldering processes, as long as their new context in relation to miniaturization is understood.
As components shrink, so do their respective stencil aperture sizes. Reduced aperture areas give rise to more challenging solder printing conditions. Traditionally, the recommended area ratio (area of the stencil opening / area of the stencil walls) is greater than 0.66; however, as component sizes have decreased, that recommendation has become relaxed.
The current smallest commercial chip (the Murata Manufacturing Co., Ltd. 008004) is 0.25 mm in length and 0.125 mm in width. The 008004 is cutting-edge technology and its diminutive size is arguably not an immediate concern to most manufacturers, however, even the larger 0.4 mm by 0.2 mm 01005 chip requires pushing past previously definitive boundaries in electronics manufacturing. 01005 chips may have aperture area ratios of approximately 0.5.
