Assembly Cost Drivers: What Actually Moves the Price Quotations for an assembly are often compared line by line, which is the least informative way to compare them. The number that moves the price is usually the one that is not broken out: the yield, the test time and the panel…

Hot Swap Controller and Inrush Limiting Plugging a board into a live backplane is an electrical event, not just a mechanical one. The bulk capacitance on the new board charges from the backplane in a few microseconds, and the current that flows is limited only by the impedance of the…

From Prototype to Production: What Changes and What Breaks A design that passes its prototype build has demonstrated that it can work. Getting it to work the same way a thousand times is a different problem, and the differences are usually not in the circuit. What Changes With Volume The…

Drop Test for Board Level Assemblies: Setup and Failure Modes A drop test reproduces the mechanical shock a product sees when it is dropped, and at board level it is used to compare designs, materials and processes rather than to certify a finished product. The test is short, the equipment…

Line Changeover: Design Rules and Process Limits A line changeover is the interval between the last good board of one product and the first good board of the next, and in a high mix environment it is often the largest single component of lost capacity. The changeover is also where…

Solder Paste Rheology and Viscosity Control in SMT Solder paste is not a simple liquid, and the number printed on its datasheet is only part of the story. Paste is a suspension of metal particles in a flux vehicle, and its flow behaviour changes with the rate at which it…

Rigid-Flex Assembly: Process Sequence and Handling A rigid flex board is assembled while flat and folded into shape afterwards. The process sequence is longer than for a rigid board, the materials are less tolerant, and the opportunities for damage are concentrated in a few steps. What a Rigid Flex Contains…

Dynamic Flex Design: Bend Radius, Grain and Copper A flexible circuit that bends once during assembly and a flexible circuit that bends a million times in service are different designs. The difference is not the material alone but the geometry of the copper and the direction in which it is…

Conformal Coating for Medical Device PCBs A medical device that runs a large current through a small board produces heat, and the surfaces it presents have to survive repeated cleaning and disinfection. Conformal coating is the usual answer, but the material only works when the board underneath it is clean…

Solder Mask Dam Width and Sliver Control on Fine Pitch Between two adjacent pads on a fine pitch board sits a thin strip of solder mask whose only job is to keep molten solder in place. That strip is the solder mask dam, and when it is too narrow the…