Placement Nozzle Selection, Wear and Management The nozzle is the last item in the placement chain before the component lands. It decides how the part is picked, how firmly it is held, and how it is released, and a worn nozzle produces placement defects that are usually blamed on the…

Through-Hole Lead Forming, Seating and Trimming Through-hole parts are still used where the mechanical strength, the current or the connector family requires them. Their leads have to be formed to fit the hole spacing and then trimmed, and the way those two steps are done decides whether the part sits…

Fiducial Design and Placement for Pick and Place Alignment A pick and place machine has to know where the board actually is before it can put a component in the right place. Fiducials are the marks that give it that reference, and their design and placement decide how accurately the…

Solder Joint Voiding Causes And Acceptance Limits A void is a bubble of gas trapped inside a solder joint, and it is present in a large fraction of the joints on a production board. In most positions it is harmless, because the joint is still electrically continuous and mechanically adequate.…

Selective Soldering For Through Hole Components A board that is mostly surface mount often still carries a connector, a transformer or a large capacitor that has to be through hole. Those parts cannot be reflowed with the rest of the assembly, and passing the whole board through a wave exposes…

Bare Board Shelf Life and Storage Control A bare board is not inert while it waits to be assembled. The copper oxidises, the finish changes, the laminate absorbs moisture and the mask cures further. The shelf life of a board is the time over which those changes stay inside the…

Selective Soldering for Mixed Technology Assemblies Most modern boards are a mixture. A densely packed surface mount area sits on one side, and a handful of connectors, transformers or power devices are still pushed through holes on the other. Sending that board across a wave solder machine would reflow the…

Component Derating for Temperature and Voltage Margin Derating is the deliberate use of a component below its rated limit so that it has margin. It costs money and board area, and it is the cheapest reliability measure available when it is applied to the parts that actually limit the life…

Moisture Sensitivity Level And Popcorning In Assembly A plastic packaged component absorbs water from the air, and the amount it absorbs depends on the material, the thickness of the body and the humidity it has been exposed to. When the part is heated rapidly in a reflow oven, that water…

Tin Whisker Risk In Lead Free Assembly A tin whisker is a single crystal of tin that grows out of a plated surface over a period of months or years. It can be a few micrometres in diameter and long enough to bridge a gap between two conductors that were…