Solder Paste Printer Setup and Squeegee Selection The printer is the first process on the line and the one that determines the quality of everything after it. A deposit that is short of volume cannot be corrected by placement, and a deposit that has slumped cannot be rescued by the…

NTC Thermistor Inrush Limiter Design An NTC thermistor used as an inrush limiter is a resistor whose value falls as it heats. It is one of the simplest ways to limit the current into a bulk capacitor, and it is also one of the most frequently misapplied components in a…

Solder Pot Contamination: Impurity Effects and Corrective Analysis A wave soldering pot is a reservoir of molten metal that is used, replenished, and contaminated over months of production. The alloy that enters the pot is not the alloy that leaves it, because copper dissolves from the boards, iron and other…

DAC Output Filter Circuit Design A digital to analog converter produces a staircase rather than a smooth waveform, and the steps carry energy at the update rate and its harmonics. The output filter removes those images and smooths the steps, and its design follows from the update rate and the…

ADC Input Buffer Circuit Design A successive approximation converter samples the input onto a small capacitor at the start of every conversion. The buffer in front of it exists to supply the charge that the sampling takes, and to present a defined impedance to the source. Why a Buffer Is…

Designing Assemblies for Wave Soldering A wave soldered assembly is designed with the process in mind or it is not designed at all. The board travels through a curtain of molten solder in one direction, and everything that the solder has to reach, and everything it must avoid, is determined…

SMT Rework And Repair Acceptance Rework is a normal part of electronics assembly, and a board that has been reworked correctly is functionally indistinguishable from one that has not. A board that has been reworked badly is worse than the board that carried the original defect, because the damage is…

Solder Joint Workmanship Standards and Acceptance Criteria A solder joint is acceptable or it is not, and the decision has to be the same whoever makes it. A written workmanship standard is what makes that possible: it defines the appearance of a good joint, describes the defects that are not…

Feeder: Key Checks Before Release A placement machine can only place what its feeders deliver, and a feeder that misfeeds, that lifts a component out of its pocket at the wrong angle, or that runs out at the wrong moment stops the line. Most of the delay in a surface…

Android Core Board Design for Compact Embedded Products An Android core board bundles the application processor, DRAM, eMMC storage and the main power tree into a compact module, so most of the product design effort moves to the carrier board underneath it. Treating that module as a plain connector-based part…