Solder Joint Grain Structure and Reliability Guide A solder joint is a metal casting on a very small scale, and like any casting it has a grain structure that depends on how it solidified. The grain structure in turn decides how the joint behaves under thermal cycling, how it cracks…

Solder Mask Registration on Fine Pitch Pads Solder mask registration is the alignment of the mask openings to the pads, and on a fine pitch design it is the item that decides whether a printable dam exists between two pads. The dam is what holds the paste in place during…

Copper Oxide Treatment for Inner Layer Bonding Inner layer copper is bonded to the resin through a treatment that grows a controlled oxide on the surface. Without it the copper and the resin do not adhere, and with the wrong one the bond is either weak or the oxide is…

Stencil Cleaning and Solder Paste Residue Control Guide A stencil that is not clean will not print consistently, and the reason is simple: the paste left in the apertures from the previous print changes the volume that the next print can deliver. Stencil cleaning is therefore a process control rather…

Approved Component Substitution Process A component shortage forces a decision: wait, or use a part that is not the one on the drawing. The second option is legitimate and it has to be managed, because an unmanaged substitution is a design change made by whoever was at the desk when…

Acceptance Class Selection for Electronics Manufacturing Every board is inspected against something. If the criteria are not written down, the inspector applies personal judgement, and the result varies between shifts, sites and customers. An acceptance class is a way to state in advance how much deviation is tolerable, so that…

Solder Paste Viscosity and Printing Window Control Guide Solder paste is a suspension of solder powder in a flux vehicle, and its viscosity is the property that decides how well it prints, how long it stays on the stencil and how much it slumps before reflow. Because the paste is…

Through Hole Soldering Method Comparison for Mixed Assemblies A board that carries both surface mount and through hole parts has to be soldered twice, and the second operation determines the quality of the through hole joints. Three methods are in common use: wave soldering with a masking pallet, selective soldering…

Pin in Paste Reflow for Through-Hole Components Pin in paste places the solder for a through hole joint as paste in the stencil, so that the joint is formed in the reflow oven rather than by a wave or by hand. It removes a process step and it puts a…

DFM Review Items Before PCB Release A design for manufacture review asks a short set of questions about a design before it is built, and the questions are the same for every board. They are asked at the point where the answers are cheap, which is before the artwork is…