Solder Preform: Design Rules and Process Limits A solder preform is a piece of solder manufactured to a specific shape and volume: a washer, a disc, a rectangle or a small formed pellet. It is placed in the joint before heating, and it melts to provide exactly the amount of…

Solder Mask Blistering After Reflow and Assembly A blister in a solder mask is a bubble that has lifted the coating away from the copper or the laminate beneath it. It may appear after reflow, after wave soldering or after the board has been in service for months, and once…

Hot Air Rework Profiles For SMT Assemblies Rework is the removal and replacement of a single component on an assembled board, and a hot air rework station is the tool used for most surface mount parts. The station applies heated air to the component and its joints, melts the solder…

Stencil Cleaning Frequency and Methods on SMT Lines A stencil is the tool that defines every solder joint on a board, and it is also the part of the process that is cleaned least often in proportion to its importance. Paste left in an aperture changes the volume of the…

Production Reporting Metrics for a PCB Shop Production reporting is the practice of putting a small number of numbers in front of the people who can change them, often enough that the numbers influence what they do next. Most shops report too much and review too rarely, which produces a…

Connector Plating Selection For PCB Headers The plating on a board mounted connector is a separable contact surface rather than a soldered joint. It has to conduct a signal or a current through a mechanical interface that may be mated once or thousands of times, and it has to keep…

Power Plane Copper Thickness and Current Capacity on PCBs A power plane is a sheet of copper that distributes current across a board, and its thickness is the parameter that decides how much current it can carry before it becomes too hot or drops too much voltage. Designers often choose…

Board Coplanarity For Connector Mounting Coplanarity is the property of a set of features lying in the same plane. For a fine pitch connector it describes how closely the solder tails or the pads of the connector lie in one plane relative to the board surface, and it decides whether…

SPI and AOI Data Correlation for Process Control on SMT SPI measures the paste before placement and AOI inspects the joints after reflow, and the two systems together describe the process from end to end. Used separately they answer single questions; used together they allow a defect to be traced…

Thermal Relief Spoke Design For Soldering A thermal relief is a pattern of narrow spokes that connects a pad to a surrounding copper plane. It exists because a pad that is connected to a plane by solid copper conducts heat away so effectively that the joint cannot be soldered: the…