Reflow Profile Design Guide A reflow profile is the temperature history that a board experiences as it passes through the soldering oven. The profile has to melt the solder at every joint, activate the flux without burning it, and complete the alloy without cooking the components. It is a curve…

Laminate Selection for High Temperature Boards Laminate selection is usually settled by price and availability until a product fails a thermal test, and then it becomes the most discussed decision on the board. The properties that matter are the ones that describe how the material behaves when it is hot,…

No Clean Flux Residue Risk on Assemblies A no clean flux is not a flux that leaves nothing behind; it is a flux whose residue has been qualified as safe for the product it is used on. That qualification depends on the environment, the voltage and the humidity, so a…

Print Stroke Speed and Stencil Separation Control in SMT Solder paste printing is a filling and releasing operation, and both halves of it are governed by speed. The squeegee has to push paste into the apertures quickly enough to be productive but slowly enough for the paste to fill them,…

Impedance Test Coupon Design And Verification A controlled impedance requirement is a promise about a transmission line, and the only way to know whether the promise was kept is to measure a line that was built with the same process as the product. That is what an impedance test coupon…

Copper Pour Design Guide A copper pour is the metal that fills the space between the traces on a layer. It is usually connected to a supply or to ground, and on most boards it covers a large fraction of the surface. The pour is often drawn automatically at the…

Thermal Via Design Guide A thermal via is a hole that moves heat rather than a signal. It is placed under a power device, in a ground pad or beneath a component that has to be cooled, and it carries heat from the top surface into the copper planes below.…

Board Support Tooling in SMT Printing and Placement A stencil is pressed onto a board with several kilograms of force, and the board has to behave like a solid plate while that happens. Thin panels, large boards and boards with cut-outs or heavy components flex under the load, and any…

Trace Width and Current Capacity in PCB Design A trace is a resistor, a heat sink and a fuse at the same time, and the current it can carry depends on how much heat it can lose. That is why the same trace width is safe on an outer layer…

BGA Inspection and Rework Practice A ball grid array hides its joints by design, which makes inspection a matter of indirect evidence and rework a matter of thermal control. Both activities are more demanding than their equivalents on a leaded package, and both depend on the same thing: knowing what…