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FEBRUARY 2021 I PCB007 MAGAZINE 55 Selecting the Right Solder Mask In the world of electronics there are multiple in- dustries each with their own requirements when it comes to solder mask. For the automotive sec- tor, solder masks are required to withstand harsh environments. In the aerospace industry, sol- der masks must meet out-gassing requirements. Over the years, white solder masks have been de- veloped that provide a high degree of reflectivity for the LED market. Solder Mask Applications Evolve Solder mask and the methods by which they were applied have evolved over the years. When non-photoimageable solder resists were intro- duced to the printed circuit board (PCB) indus- try, silk screen printing was the common method of application. As the demand for real estate on PCB designs increased, photoimageable solder masks were developed. e popularity of photo- imageable solder masks introduced new applica- tion systems such as double-sided screen print- ing, curtain coating and spray systems. ese methods of application have been around for many years and are still being used today. In the past five years, several other application process- es have been reintroduced to the market includ- ing ink jet and photoimageable dry film. Advances in Solder Mask Imaging As technologies advance and offer more func- tions, PCBs have become more populated with the miniaturization of key components. e advancements have pushed the boundaries on image registration using conventional expos- ing units. Over the years, direct imaging (DI) systems were introduced to the PCB indus- try to help alleviate the challenge. e DI sys- tems provide different wavelengths in com- parison to conventional exposing units. Solder mask manufacturers, working side-by-side with equipment manufacturers, developed DI solder masks that are better suited for these types of imaging systems. To Flex or Not to Flex Solder masks have some degree of pliability. inner PCBs that are not categorized as a flex build can sometimes encounter a degree of bending due to handling or manufactur- ing processes. Depending on the amount the substrates are bent, they can exhibit a degree of fracturing. Fracturing of the solder mask is not the same as corner cracking caused by ex- posure to harsh environments. In cases such as this, PCB manufacturers and contract elec- tronics manufacturers (CEM) should consider the use of a flexible solder mask. Solder Masks Are Not Only Green Solder masks have evolved from green to sev- eral other colors over the years. e most com- mon colors besides green are black, blue, red, white, and yellow—all of which fall in the fam- ily of primary colors. Colors were developed and brought to market at the request of origi- nal equipment manufacturers (OEMs). Col- ored solder mask can be used for identifying prototypes, revision changes, manufacturing facilities, or for cosmetic reasons. Colored sol- der masks can also be combined in measured amounts to create a vast number of other col- ors such as orange, purple and brown. Sol- der masks can also have various surface finish- es such as matte, glossy, or somewhere in be- tween, depending on customers' requirements. 1 2 4 5 3 Established 30 years ago, Taiyo America Inc. is a subsidiary of Taiyo Holdings Co. Ltd., the world's leading manufacturer of specialty inks and solder masks for printed circuit boards. Taiyo offers conductive inks for manufacturing printed electronics. Visit us online at: Taiyo-america.com.