Through-Hole Assembly Options for Mixed Technology Boards

摘要

Surface mount assembly has dominated its through-hole predecessor since the early 1990s. The higher density and lowerrnultimate cost of SMT makes it a preferred assembly technology. However, the mechanical strength of through-holernconnections continues to make through-hole the technology of choice in assembling connectors. This presentation willrndescribe the primary methods currently used for through-hole connector assembly: 1) selective wave solder, 2) pin-in-pastern(PIP), reflow, 3) hand soldering and 4) solder preforms. We will show how solder preforms are an excellent alternative whenrnPIP provides insufficient solder.rnThe wave solder method requires specialized equipment and processes to solder connectors. Pin-in-paste reflow evolved as arnway to accomplish through-hole assembly without additional equipment or process steps. In the PIP method, the additionalrnsolder required to fill the though-hole barrel is deposited by overprinting the pad in the area of each connector pin, usingrnstandard SMT equipment. During reflow, the solder wicks to each pin forming the solder fillet.rnThis paper explains why pin-through-paste reflow methods based on overprinting solder paste have become more challengingrndue to an increasing use of Organic Solderability Preservative (OSP), fine-feature devices (e.g. fine pitch connectors) andrndensely populated PCB layout designs that conflict with requirements for successful use of step-stencils. This paper alsornshows an example where solder preforms were used to provide extra solder volume for each pin. This work demonstratesrnhow solder preforms provide a viable manufacturing solution to ensure complete through-hole solder joints.