Solder Stencil Printing On Deep Cavity

In the past when flip chip assembly on a metal substrate was implemented, these presented a challenge in solder paste printing using stencil on a cavity-formed space. The main restrictor is the cavity depth on a limited area (less than 2.0 mm). Hence, an approach was to solder dispensing using a multi-hole dispense nozzle. This created challenges on the nozzle hole clogging resulting in inconsistencies and unacceptable volume deposited. Several iterations in the nozzle hole design and solder powder size consistency improved the performance but not to the expected level. Stencil printing technologies have been in use in the industry for many years. However, the conventional 2D stencil technology is primarily applicable and mostly used in flat surfaces. Recently, stencil manufacturers developed new stencil technology capable of printing on a 100 microns depth or less. The most recent development of printing solder paste is by using a 3D stencil paired with a specially designed squeegee to achieve a good and consistent print deposit in constrained and limited spaces. This study is on solder paste printing using 3D stencil on a 300-micrometer cavity and less than 2.0-millimeter area. It is feasible to form an array of solder deposits on the limited-spaced cavity. Another study is printing on a 150-micrometer cavity spaced at 400 micrometers apart. The 3D stencil allows for a more controlled solder deposit on cavity-formed spaces. Several factors affect the quality of print deposits - solder type, stencil layout, type of squeegee, cavity layout and depth, as well the printing parameters used. The interactions of these elements make possible solder paste printing on a deep cavity spaced in array.