Nano Coating: Design Rules and Process Limits A nano coating is a thin chemical film applied to the walls of a stencil to change how paste behaves at the aperture. The claim is simple: less paste sticks to the wall, so the deposit is more complete and the underside of…

Stencil Foil Tension: Frame Care and Paste Release A stainless stencil is a spring, and like any spring it only behaves predictably while it is stretched. Stencil foil tension, the force that keeps the mesh and the foil flat between the frame members, decides how the foil behaves when the…

Thermal Pad Voiding Control A thermal pad is a large area of paste that has to reflow into a thin, continuous layer between a component and the board. Because the area is large and the gap is small, the volatiles from the flux have very little room to escape, and…

Shear and Pull Testing of Solder Joints A solder joint can be pulled, sheared or bent, and each test measures a different property. The result is a number that describes the joint and the process that made it, and it is only comparable with another number taken the same way.…

Fabrication Audit Checklist and Records An audit is a walk through a shop comparing what is written with what is done, and the records are what make the comparison possible. A shop that runs a good process and keeps poor records fails an audit, and a shop that keeps good…

Line Balance and Buffer Size on an SMT Line Line balance is the gap between the rate a line can produce and the rate it actually produces once the stations have to wait for one another. On an SMT line the constraints are rarely the placement machines, which run at…

AOI Programming: Design Rules and Process Limits Automated optical inspection only earns its place if it finds the defects that matter without flooding the line with calls that are not defects. The difference between a useful program and an expensive one is almost entirely in the programming, and the work…

Placement Program Optimization and Cycle Time A placement program decides the order in which the parts are placed and the nozzles that are used, and two programs for the same board can differ in cycle time without any difference in the hardware. The optimization is a scheduling problem with constraints.…

Print Alignment Verification and Offset Control The paste has to land on the pad, and the printer aligns the stencil to the board using fiducials. A small offset reduces the solderable area and a larger one puts paste on the mask, and the two consequences are different. How the Printer…

Glass Transition Temperature and Its Use in PCB A laminate has a temperature at which its mechanical behaviour changes, and the change is what the glass transition temperature describes. Above it the material expands faster and becomes softer, which is the condition the assembly processes create. What the Transition Is…