Solder Paste Inspection Data and Process Feedback Guide A paste inspection system measures the deposit that the printer has just produced, and its real value is not the pass or fail decision on a single board. It is the data that the system generates across a run, which shows when…

Water Soluble Flux Process Control and Cleaning Guide A water soluble flux is formulated so that its residue can be removed in water, which allows a more active chemistry to be used than a no clean product would permit. The trade is explicit: the flux solders more reliably on a…

Underfill: Preparation, Placement and Process Control Underfill is the material that is drawn beneath an area array package to distribute the strain between the solder joints and the board. It is applied as a bead along the edge of the package and then flows by capillary action until the gap…

Assembly Pallet and Fixture Design for SMT Production A pallet is the carrier that holds a board through the assembly line, and a well designed one is invisible: the board sits flat, the fiducials are visible, the conveyor grips it and nothing moves. A badly designed one produces placement errors,…

Board Cleaning After Reflow in Mixed Assembly Lines Board cleaning after reflow is a line integration problem as much as a chemistry problem. The cleaner has to sit between the reflow oven and the next operation, accept the same panel size and throughput, and deliver a dry board at the…

Photoresist Selection for Inner Layer Imaging Guide On an inner layer the photoresist is the stencil for the etch, and its properties decide the finest line the shop can hold and the defect rate it can live with. Choosing a resist is therefore a matter of matching its resolution, its…

Solder Mask Bleed and Pad Clearance Control in Design Solder mask bleed is the encroachment of the cured mask onto a pad opening, and it is a design and process interaction rather than a defect in the ink. A small amount is normal and allowed for in every design, but…

Laser Direct Imaging: Key Checks Before Release Laser direct imaging exposes the photoresist by scanning the artwork with a modulated beam instead of projecting it through a film. The technique removes the film, the contact frame and the vacuum drawdown from the imaging step, and in doing so it removes…

Operator Certification and Training Operator certification is the mechanism that connects a written procedure to a person who can actually perform it. Where certification is meaningful, it is based on observed work rather than on attendance, it is specific to the process and the product class, and it is renewed.…

End of Line Packing and Protection Packing is the last process before the product leaves the building, and it is the one that determines whether everything done before it arrives intact. A board that has been assembled, tested and coated can still be damaged by the wrong carton, a bag…