Test Point Design For In Circuit Test Fixtures In circuit test works by pressing a bed of nails against the underside of the board and measuring each net. The nails are spring loaded probes, and each one has to land on a surface that is flat, clean, of a known…

Microvia Reliability Design Guide A microvia is a small hole, usually below 0.15 mm in diameter, that connects two adjacent layers in a high density board. It is drilled with a laser rather than with a mechanical bit, and it is the feature that allows a fine pitch device to…

Fiducial: Key Checks Before Release Every automated machine on an assembly line finds the board before it does anything else. The fiducial is the mark it finds, and the accuracy of the whole operation depends on how well that mark is made. A printer, a placer, an optical inspection system…

Silkscreen Legibility Rules Guide Silkscreen legibility is the difference between a board that can be assembled and repaired by anyone and one that requires the layout file to be opened. The markings carry reference designators, polarity marks, pin one indicators and version numbers, and every one of them is printed…

PCB Silkscreen Legend And Clearance Rules The silkscreen, or legend, is the printed information on a board that a human reads: the reference designators, the polarity marks, the connector pin numbers, the part outlines and the warnings. It is the cheapest layer of the board and the one most often…

Component Clearance: Preparation, Placement and Process Control Component clearance is the space that two parts need between them, and it is always larger than the space they occupy. The extra distance is for the placement nozzle, the soldering process, the inspection camera and the rework tool. A board that is…

Length Matching and Timing Skew Control in PCB Routing Two signals that leave a driver at the same instant must arrive at the receiver within a defined window of each other, or the interface will read the wrong data. Length matching is the practice of adjusting trace lengths so that…

Differential Pair: Preparation, Placement and Process Control A differential pair carries a signal on two conductors and reads the difference between them. That arrangement rejects common mode noise, halves the effective switching current and gives a predictable impedance, but only if the two traces stay coupled and matched along the…

Conformal Coating Masking And Keepout Design Conformal coating is applied after assembly to protect the board from moisture, contamination and electrochemical migration, and the coating has to be kept away from the features that must remain accessible or that cannot tolerate it. That is the masking requirement, and it is…

BGA Escape Routing Design Guide BGA escape routing is the work that a ball grid array forces on the designer before any functional trace can be drawn. The package hides its connections underneath, so every signal has to be routed out from the inside of the array to the rest…