chapter 8 of our comprehensive guide to stencils looks at considerations for glue and pin-in-hole reflow
Epoxy glue is used as a surface mount adhesive (SMA) to attach and maintain surface mount devices (SMD) to the PCB surface throughout placement and wave soldering. As such, thicker stencils which enable increased adhesive deposits are required.
Since the development of single component epoxy technology for use as a SMA, the methods of application themselves have evolved, driven by the requirements for increased assembly speed and improved process repeatability.
Adhesive stencil printing utilises existing production technology and techniques to optimise the efficiency required from a surface mount line, particularly relevant when densely populated assemblies are processed. Total print times of less than 15 seconds are achievable.
Pin-in-hole reflow (PIHR)
This assembly technique is used extensively as an alternative for subsequent hand or wave soldering operations of leaded components – from crystal oscillators and headers to multi-row connectors.
As with all surface mount technology, successful end product quality relies on the accuracy and adequacy of the printed solder paste deposits. Optimised stencil design is an essential requirement to ensure the printing solution delivers successful PIHR results.
In its simplest form, the technique involves printing solder paste onto the printed circuit board for both surface mount devices and leaded components. With PIHR it is essential that sufficient paste volume is available to ensure the required solder fillets are formed on the top and bottom sides of the PCB and in the component holes.
Following insertion of leaded components and placement of surface mount devices the assembly is reflowed. Shorter product cycle-times, reductions in manufacturing costs and elimination of contamination by second operation flux deposits are the main benefits.
There are basic guidelines and considerations, which need to be followed to ensure success using this process.