Hardware Design Review Checkpoints That Catch Errors Most of the errors that reach a prototype are not logic errors. The schematic is usually correct in the sense that it implements the intended function, and the layout passes its design rule check. The failures that appear at bring up are usually…

Managing Component Obsolescence and Last Time Buy Decisions Every product eventually runs into a part that is no longer available. A semiconductor vendor discontinues a package, a connector series is replaced, or a passive component is moved to a different factory with a different end of life date. Handling that…

Infrared Remote Receiver Circuit Design An infrared remote link is cheap, simple and remarkably robust, provided the receiver is treated as the analogue device it really is. The module on the board contains a photodiode, an amplifier and a demodulator, and it outputs a clean logic signal only when the…

Choosing A Flex Substrate Or A Rigid Board The material at the bottom of a board is usually decided by the layout engineer on the basis of what the previous design used. That habit is reasonable for a product that has not changed, and it is a source of avoidable…

Military Grade Chip Resistor Screening And Reliability A chip resistor bought on price and a chip resistor bought against a military specification look the same and measure the same on the bench. The difference appears in the qualification data behind them, in the screening that each unit has passed, and…

Load Switch and eFuse Circuit Design Almost every board has at least one rail that has to be turned on and off under software control, or protected against a fault on a downstream module. A load switch does the first, an eFuse does the second, and the two are often…

Stencil Cleaning, Storage and Inspection A stencil is a consumable that behaves like a precision tool, and it is treated as neither. Most paste volume problems that are blamed on the printer or the profile begin with a stencil that was not cleaned, not stored or not inspected. Why Cleanliness…

Solder Paste Storage, Working Life and Handling Solder paste is a chemical product with a shelf life, a working window and a sensitivity to how it is handled. Most of the variation that appears in a print between the start and the end of a shift comes from the paste…

Instant Water Heater: Design Rules and Process Limits An instantaneous water heater switches several kilowatts of resistive load under the control of a small electronic board, and it does so in a wet environment with a person standing next to it. Almost every design decision follows from that sentence. What…

Spirometer Circuit Design: Pressure to Flow A spirometer turns a pressure difference into a flow, and a flow into a volume. The electronics are simple in principle, and the accuracy of the instrument depends almost entirely on the sensor, the conditioning around it and the calibration of the whole path.…