Silkscreen: Design Rules and Process Limits The legend on a board is not decoration. It is the only reliable way for an operator, a test technician, or a repair engineer to know which component goes where, how it is oriented, and which pin is the first one. A board without…

ENEPIG And Wire Bondable Pad Finishes Some boards have to do two jobs at once. A board that carries a module, a bare die, or a hybrid circuit has pads that are soldered and pads that are wire bonded, and the same surface finish has to serve both. The solder…

Board Level Drop Test and Its Limitations A drop test is used to qualify a product for the handling it will see, and it is often required before a design is released. It also produces results that are easy to misread. What the Test Applies The test applies a large…

Underfill For BGA And CSP Drop Reliability An area array joint is a small ball of solder between a package and a pad, and it is much stronger in shear than in tension. A drop, a bend, or a shock puts the joint into tension, and the failure occurs at…

Thermocouple Cold Junction Compensation Design A thermocouple produces a voltage proportional to the temperature difference between its two junctions, not to the temperature of the hot one. Everything the circuit does afterwards is about establishing what the cold junction temperature is, and that is where most of the error comes…

Selecting a Potting Compound for Rugged Electronic Products An assembly that must survive water, vibration, salt and impact is often protected by surrounding it with a solid material. Potting and encapsulation replace the air around a board with a potting compound that supports the components, excludes moisture and spreads mechanical…

Test Coverage Analysis by Fault Class Test coverage is usually reported as a percentage, and the percentage on its own says very little. What it measures and what it excludes decide whether the figure describes the risk. What Coverage Measures The common measure is the proportion of nets or of…

Solder Paste Printing for Mixed Pitch Boards A board that carries both a fine pitch part and a large connector cannot be printed with one set of parameters, and the compromise is usually made in favour of whichever part is inspected more. Where the Conflict Comes From The fine pitch…

Thermal Relief Design and Its Effect on Soldering A thermal relief is a connection to a plane that is narrower than the pad it serves. It exists to limit how quickly heat leaves the pad during soldering, and it is the reason some joints form easily and some do not.…

Thermal Relief: Practical Checks for Production A pad that connects to a ground plane is connected to a great deal of copper, and that copper carries heat away from the joint during soldering. The result is a pad that does not reach the soldering temperature while its neighbours do, and…