Wire Harness Routing and Strain Relief at the Board A connector on a board carries the electrical interface, but the mechanical interface belongs to whatever holds the cable. If that is the solder joint itself, the joint will eventually crack, because a harness transmits every pull, every vibration and every…

Underfill and Corner Bonding for BGA Board Level Reliability A ball grid array joint has to survive thousands of thermal cycles while the package and the board expand at different rates. Underfill is the material that spreads that strain across the whole array instead of concentrating it in the corner…

Bow and Twist Measurement in PCB Fabrication A board that is not flat is difficult to print, difficult to place components on, and difficult to fit into an enclosure. Bow and twist are the two numbers that describe how far the board departs from a plane, and they are measured…

Annular Ring Requirements and Design Rules The annular ring is the copper that remains around a drilled hole after the drill has taken its share of the pad. It carries the connection between the hole and the trace, and if it is too small the result is a breakout, a…

Moisture Sensitivity Level Handling and Baking A plastic package that has absorbed moisture will crack during reflow. The water flashes to steam, the internal pressure rises, and the package delaminates or bursts in a failure mode called popcorning. Manufacturers classify every component with a moisture sensitivity level that says how…

What HDI Inspection Standards Actually Check A high density interconnect board cannot be judged by the same inspection criteria as a conventional multilayer board. The features are smaller, the layers are thinner, and the critical defects are hidden inside the build-up structure where a visual check cannot reach them. An…

RF Design: Interconnect Rules That Cut Return Loss Data rates that once belonged to radio equipment now appear on ordinary digital boards, and at those rates the interconnect stops behaving like a wire and starts behaving like a transmission line. Reflections, crosstalk and radiation appear wherever the geometry changes. This…

Junction Temperature: Thermal Design Practice for Electronic Assemblies An active electronic device is a source of heat that has to be removed, and the practice of thermal design is mostly about identifying which of the series resistances dominates and addressing that one rather than the others. The exercise is short…

Bill Of Materials: Design Rules and Process Limits The bill of materials is the document that turns a design into a product. It tells the buyer what to order, the store what to hold, the line what to place and the test engineer what to expect. When the bill of…

Solder Mask Design: Openings, Dams and Tenting Soldermask is often treated as a cosmetic layer, and it is anything but. It defines where solder may go, protects the conductors from the environment and from handling, and its openings constrain the stencil and the component footprint. What the Mask Has to…