The Assembly Drawing and What It Must Carry An assembly drawing is the document that tells the production floor what to build, and it is usually the least maintained document in the package. Where it is wrong, the board is built wrongly and the mistake is invisible until test. What…

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…

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…

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…

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…

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…

PCB Laminate Storage, Shelf Life and Moisture Control Laminate is a chemically active material that keeps changing after it leaves the supplier. Prepreg continues to advance its cure, cores absorb moisture from the air, and a roll left in the wrong corner of the store can turn a proven lamination…

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…

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…