The Improvement on Thermal Resistance of Liquid Photosenstive Solder Mask

• Main Authors: Sen-Chin Yang, 楊森智
• Other Authors: Tsung-Han Ho
• Format: Others
• Language: zh-TW
• Published: 101
• Online Access: http://ndltd.ncl.edu.tw/handle/21745330380608756811

碩士 === 國立高雄應用科技大學 === 化學工程與材料工程系 === 100 === Based on the Restriction of Hazardous Substances Directive implemented by the European Union in 2006, the lead solder must be prohibited in a process for manufacture of PCBs and replaced by lead-free solder. However, some characteristics of components and printed circuit boards such as heat resistance and moisture resistance also need to be improved correspondingly due to higher melting points of soldering materials applied in the lead-free solder process. As one common material in the existing process of manufacturing PCBs, the liquid solder mask first introduced in this study is negative photoresist composed of materials such as photoinitiator, reactive monomer, thermocured resin, photosensitive oligomer, additive and solvent, wherein the thermocured resin is critical to improvement in heat resistance of solder mask in this study. Secondarily, we introduce the equipment, techniques and steps available in a general PCB factory for the process with solder masks by which the readers will be further familiar with solder mask and current status. To improve heat resistance of solder mask, we have a strategy of adjusting one ingredient in the solder mask, i.e., thermocured resin which is directly correlated with heat resistance, by choosing three types of epoxy resins, e.g., O-Cresol Novalac, Phenol, and DGEBA, mostly available in the market for manufacture and tests of solder mask. In view of three epoxy resins’ different characteristics in heat resistance required to be identified first, the number of epoxy and the content of each ingredient in the designed formula must be constantly controlled without the raw materials’ distinct numbers of epoxy affecting reactivity. Next, the prepared solder mask as the material used in the PCB process is applied on one PCB substrate. During the manufacturing process, there is no significant difference observed in the performance of light curing among three types of solder mask exposed and developed that demonstrates the factors critical to reactivity such as acid value and number of epoxy are stably controlled with an identical mater agent mixed with each of three epoxy resins, respectively. Furthermore, it can be seen from performance of master ink stripped that O-Cresol Novalac with a better operating width is advantageous to fast dryness of heated ink, which can be demonstrated according to ink’s reactivity in FTIR and status of solder adhered to PCBs, and indicates the best heat resistance in experiments. However, DGEBA epoxy manifests the best heat resistance because of the step of coating with ink plugged into holes during our tests for solder mask adhered to and plugging holes. In contrast to heat resistance, ink’s flexibility is crucial and solder mask with insignificant hardening contraction inclines to be an uncracked condition which causes peeling of solder masks with tin fluid having infiltrated.