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APRIL 2019 I PCB007 MAGAZINE 87 In case of insufficient microetching, the cop- per surface will show a dark color when ex- posed to air (Figure 4). The discoloration is due to the formation of cupric oxide. This type of oxidation will diminish solderability and further impact solder joint reliability. When the OSP film is too thin or not properly formed over the copper surface, oxygen can more eas- ily reach the copper surface, which leads to discoloration. With increased exposure time and temperatures, the color of the copper layer changed from yellow to red-brown. The discoloration is particularly troublesome when complex assembly and advanced pack- aging applications are in use. With respect to the latter, the solder ball attachment equip- ment must visually detect the solder ball point; in turn, this is required for the machine to be properly aligned with the OSP-coated bonding pad. The discoloration will interfere with the machine vision system and lead to low yields. While a light discoloration shown in Figure 5 will most likely not adversely affect solderabil- ity, such a condition will interfere with proper solder ball alignment to the BGA feature. PCB007 Michael Carano is VP of technology and business development for RBP Chemical Technology. To read past columns or contact Carano, click here. Figure 4: Surface showing both discoloration and normal copper surface after processing in OSP. Figure 5: Slight discoloration of OSP-protected copper with arrows pointing to discoloration. Does inkjet solder resist have the potential for volume production? Mariana Van Dam, global sales manager of PCB imaging solutions, and Dr. Frank Louwet, business unit manager of advanced coatings and chemicals, speak with I-Connect007 Technical Editor Pete Starkey about Agfa's latest developments, plus some novel applications for inkjet etch and plating resists. The group discusses inkjet solder mask development at Agfa, and how they are validating the ink at a selective number of customer sites over the past year. "Optimiza- tion between ink, printer, and software requires a lot of capacity. Cooperating at a specific customer site builds a lot of know-how, and the ink and system are tuned to one another. Doing this effort in parallel for all printers would be tough to organize, but we are open to cooperate with any and all worldwide," said Louwet. To read this interview, click here. (Source: I-Connect007) Agfa on Revolutionary Inkjet Solder Mask Applications

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