LEAD-FREE SOLDER PASTE DEVELOPMENT FOR ULTRA FINE-PITCH PRINTING AND REFLOW OF 03015 AND 0201 METRIC CHIP COMPONENTS

摘要

Due to the widespread popularity in mobile devices such as wearable devices and smartphones, demand for miniaturized or micro surface mount components, such as 0201 metric chip, flip chip packages, and fine-pitch surface mount land patterns to accommodate them are increasing. Consequently, solder paste is required to be compatible with this high-density surface mount technology. When printing paste for 0402 metric chip components, stencil apertures of approximately 0.2mm diameter are used whereas for 0201 metric chip components, stencil apertures of the dimension 0.1mm diameter are needed. This presents challenges for both good printability and solderability. Conventional solder paste technology seems to be lacking in coping up with these stringent requirements. Precise printability' and optimum solder reflow parameters were evaluated on ultra-fine pitch surface mount board pads using conventional solder paste and a newly developed solder paste to understand compatibility with 0201 and 03015 metric chip components. A test vehicle was used with 0402, 03015 and 0201 metric chip components. Type 5~(1)) (10-25um) and Type 6 (5-20um) no-clean lead-free Sn3Ag0.5Cu solder pastes were evaluated with two different stencil thicknesses,50um and 80um. The area apertures ratios varied from 0.28 to 0.94. The measurements of paste volume after printing were recorded using production solder paste inspection equipment. After printing reflow studies were conducted on assembled 03015R and 0201C metric chip components to understand reflow behavior. The solder paste development included flux improvement to increase stencil release rate of the solder paste through the stencil apertures for the challenging stencil area aperture ratios used. The newly engineered heat resistant flux chemistry in the solder paste helped to reduce solder graping during reflow even with the small paste deposits on the board. Continual solder paste print studies as well as print to pause studies were conducted with the developed solder paste on 0201 metric and 0.3mm pitch QFP board land pads to understand the use of the solder paste in production. The results of the work will be discussed in detail.