SUMMER 2021

50 THE DISTRIBUTOR’S

50 THE DISTRIBUTOR’S LINK PENN ENGINEERING 5190 Old Easton Road, Danboro, PA 18916 TEL 1-800-237-4736 FAX 215-766-0143 EMAIL info@pemnet.com WEB www.pemnet.com UTILIZING SURFACE MOUNT TECHNOLOGY FOR MECHANICAL FASTENING TO PCBS by Michael J. Rossi, Marketing Services Supervisor Historically, electronics manufacturers faced a difficult choice when assembling printed circuit boards. They could deal with the inconvenience and poor productivity of loose fastening hardware, or they could use broaching fasteners that hold circuit boards securely but can easily damage fully populated boards when not installed properly. However, fasteners designed with Surface Mount Technology (SMT) provide a technically superior alternative for PCB assembly. The surface-mount installation method uses a system in which various types of fasteners are adhered directly onto a solder pad on the surface of the PCB, using the same soldering processes as the board’s other electronic components. Before discussing the advantages of SMT fasteners, let’s examine some traditional fastening options and the potential drawbacks of their use. Traditional Methods Of Fastening Hardware To PCBs Loose Spacers The most common method for fastening hardware to PCBs is the use of loose spacers. They are often in the form of plastic or metal columns used to offset two boards. The spacers must be placed secondarily, sometimes snapping onto the board, sometimes screwing together with another component. This secondary process is typically performed manually, which is quite time consuming and labor-intensive. Loose Nuts and Screws Loose nuts and screws are handled much the same. Used during assembly, handling can be an issue because of the detailed work that is necessary to align all of the parts typically on both sides of the PC board. Care must be taken so that any dropped hardware is identified and removed so as to not cause rattle, or worse, shorts and product failure. Broaching Spacers or Nuts To avoid the use of loose hardware and help simplify the assembly process, some manufacturers utilize broaching spacers or nuts. The hardware permanently fastens to the PCB so that handling becomes simpler by eliminating one of the loose components. The broaching, however, is achieved by pressing a knurled component into a slightly smaller hole in the board, forcing the knurls to cut into the board. If done wrong, this method can cause issues with board integrity. Problems can also occur during the installation process if the parts are misaligned while being pressed into the mounting hole. Other attachment methods such as adhesives do exist, and all have both advantages and disadvantages. But one common factor is they all must be placed on the board or assembled – which represents a cost, typically in manual labor, which can be very high. And with each additional touch to the board, the chances for damage and quality issues increase. TECHNICAL ARTICLE CONTINUED ON PAGE 126