Moisture Sensitivity Level And Why Dry Storage Matters Plastic packaged components absorb water from the air. It is a slow process and an invisible one, and it matters only when the part is heated rapidly, which is exactly what a reflow oven does. The water turns to steam inside the…

Flip Chip Bumping and Copper Pillar Interconnects Flip chip assembly turns the die face down and connects it to the substrate through an array of bumps rather than through wire bonds around the perimeter. The change shortens the electrical path, improves thermal performance and allows far more connections on the…

Heat Sink Attachment and Thermal Interface Materials Fitting a heat sink looks like a mechanical task, but most of the thermal performance is decided by what happens at the interface. Two surfaces that appear flat touch only at microscopic high points, and the air between them is one of the…

Second Source: Second-Source Qualification: Proving a Replacement Is Equivalent A second source is introduced to reduce risk, and introducing one carelessly creates a different risk in its place. The work is in demonstrating that the replacement behaves like the original in the ways that matter, which is usually a smaller…

Thermoelectric Cooler Driver Design Guide A thermoelectric cooler moves heat rather than generating cold, and the amount it moves depends on the current through it in a way that is close to linear. That makes the drive circuit a precision current source rather than a power switch, and it makes…

Solder Alloy Selection: SAC305, Low Temperature and High Temperature The alloy in a solder joint is chosen once and then inherited by every product that follows. It determines the reflow temperature, the joint strength, the behaviour at high temperature and the cost, and the trade is different for each product.…

Conductive Foam That Survives Reflow: What To Specify Shielding a board used to mean a metal finger strip or a die cut gasket fitted by hand, with a conductive adhesive to bond it. As products have become smaller and production has become automated, that approach has run into two limits…

Black Pad in ENIG: Causes and Solder Joint Failure Black pad is the name given to a dark, brittle layer that forms on the nickel surface of an electroless nickel immersion gold finish, and it produces solder joints that look acceptable and fail without warning. The gold itself is not…

Reducing SI/PI Design Iterations On A Wearable Board A wearable device compresses a radio, a processor and a memory interface into a volume smaller than a matchbox, and the memory bus is usually the part that causes the trouble. The interface runs fast, the supply is shared with everything else,…

Hot Bar Soldering: Thermode Process Control for FPC Hot bar soldering joins a flex circuit to a rigid board with a heated metal bar pressed onto a row of pads. The process is fast, it can be reworked, and it produces joints that withstand flexing better than a hand soldered…