Fine pitch and low area ratio stencil printing process

Fine pitch and low area ratio printing is a necessity for modern electronics assembly. The necessity arises due to reduction of the space on printed circuit boards. On the other hand, it represents new technology challenges in the printing of electronics materials, such as solder paste, and this type of printing is difficult to apply in practice. Fine pitch and low area ratio printing pose difficulties as it does not follow the traditional rules of solder paste stencil printing. Fine pitch and low area ratio stencils have area ratio value less than the traditionally designated value, which is 0.66. It is believed that if these processes are studied carefully then better print quality can be achieved with cost effective solutions. In the 1990s through 2000s, this type of study was conducted with small electronics components such as 0402s, 0201s, and 01005s. Even at that time, it was difficult to print solders with apertures designed for those components; with today's even smaller volume printing needs, the challenges are intensified. It is necessary to have that process be cost effective. Cost effectiveness implies that the current material sets and equipment like the stencil printer, the stencils, and the solder paste is not drastically altered from those currently used in practice for non-fine pitch printing. There are two major sub-processes of an electronics material screen printing process, namely, the fill process and the release process. While there has been a significant prior study on the release process, comparatively, the fill process has been neglected. This research studies the fill aspect of the fine pitch and low area ratio printing process and focuses on analyzing the transfer efficiency of small volume deposits for BGA components. Three different experiments are conducted to study a cost effective fill process. The most effective process by which transfer efficiency can be increased is by reducing the attack angle of the squeegee blades.