Solder Mask Adhesion Testing and Failure Diagnosis Solder mask is expected to stay in place for the life of a product, yet it is only a thin polymer film bonded to copper and laminate. When that bond is weak, the mask lifts, blisters or undercuts during reflow, wave soldering or…

Panel Plating Versus Pattern Plating In Fabrication Two plating sequences are used to build the copper on a printed circuit board, and the difference between them is the order in which the plating and the imaging happen. In one, the copper is plated over the whole panel and then etched…

Resistor Network Matching Design A resistor network is several resistive elements on one substrate in one package. It is bought not for its absolute accuracy but for the match between its elements, and understanding that distinction is what makes the part worth its price. Absolute Tolerance and Ratio Tolerance absolute…

Flex Circuit Bend Radius And Bend Life A flexible circuit is designed to bend, and the amount it can bend without damage is a design property rather than a property of the material alone. The bend radius, the number of bends the product will see, the direction of the bend…

Component Polarity And Orientation Verification A component that is placed in the right position but rotated by a hundred and eighty degrees passes every positional check in the machine. It sits flat, its terminals land on the pads, and the paste wets on both ends, so the placement system reports…

Voltage Divider Accuracy Design A voltage divider is two resistors and a ratio, and it appears in almost every analog circuit. Its accuracy is usually worse than the designer expects, because the errors that matter are the ratio errors and the loading, not the absolute values. The Ratio and Its…

SMT Line Balance and Throughput Planning An SMT line balance is achieved when no station waits for another and no station is the reason the line stops. In practice the balance point moves with every product change, so the exercise is less about a single calculation and more about knowing…

Solder Mask Plug and Via in Pad on Dense Boards A via that is left open in the solder mask is a small hole with a large appetite. Paste, flux and wash liquid all find their way into it, and the consequences show up on the assembly line rather than…

Analog Comparator Circuit Design A comparator answers a question: is the input above the reference or below it. It is often implemented with an operational amplifier, and that is the first mistake, because an amplifier and a comparator are optimised for different things. Why Not an Operational Amplifier An operational…

Thermal Simulation And CFD For PCB Designs A thermal simulation predicts how hot a circuit will run before the board exists. It answers two questions that a calculation on a datasheet cannot: how much of the heat leaves through the copper rather than through the package, and how much the…