Application of Solder Paste In PCB Cavities

Abstract

ABSTRACT Two major drivers in the electronics industry are electrical and mechanical miniaturization. Whereas lines and spaces have been getting smaller over the years (current HDI standard is 50/50μm), mechanical miniaturization has thus far been mostly limited to decreasing layer-count and material thickness. One further solution is local height reduction through the introduction of recessed cavities on the PCB. These cavities can be used assembling components and/or device elements to reduce overall PCBA z-axis dimension. The cavity forming method referred to in this paper allows for unlimited flexibility in shape and depth of these cavities, thereby enabling greater freedom in material selection and PCB design rules. Solderable surfaces and soldermask patterns can also be applied on the cavity layer. As much as this provides a solution for z-axis miniaturization, the challenge of assembling components with standard and even advanced surface mount technologies remains a critical aspect of successful implementation of these technologies. This paper aims to demonstrate initial trials to address the challenge of component assembly within recessed cavities on the PCB using various stencil configurations. Two major proponents of the trials presented here are AT&S with its 2.5D® Technology and Christian Koenen GmbH, astencil manufacturer. The ultimate target of these trials and this paper is not a final and universal solution, but rather attempts to clarify the initial challenge scope and explore existing or further possible solutions.