Differential Pair Routing: Rules That Actually Matter Differential pairs are surrounded by more folklore than almost any other part of high speed layout. Some of the advice is essential, some of it is a convention that no longer applies, and the difference shows up when a design fails its eye…

PCB Fiducials: Placement Rules for Machine Alignment A fiducial is a small copper mark on the board that exists only for a machine to look at. It carries no signal, it is not part of the circuit, and if it is missing, covered or badly placed, the entire assembly line…

PCB Drilling: Hole Types, Tolerances and Limits Drilling is the step where a circuit board stops being a flat sheet and starts being a three dimensional structure, and it is the operation with the most potential to damage a design. A hole that is slightly the wrong size, slightly the…

IC Substrate: How Package Substrates Differ From PCBs An IC substrate is the small board inside a chip package, and it is made with the same family of processes as a PCB while being a different product in almost every respect. It exists because a silicon die and a printed…

From Prototype to Production: What Changes on the PCB The gap between a working prototype and a stable production board is wider than most teams expect. The prototype proves that the design functions. Production has to prove that the same design can be built thousands of times, by a different…

PCB Minimum Order Quantity: Why It Exists and How to Work With It A minimum order quantity is one of the most common points of friction between a buyer and a circuit board supplier, and it is usually presented as an arbitrary rule. In practice it is an economic limit…

Small Batch PCB Assembly: Cost, Process and Trade-offs Small batch assembly is a different business from volume assembly, and the difference is not just the quantity. At a few hundred boards the price is dominated by setup, the components are the hardest part of the job, and the process that…

In-Circuit Test: Test Points, Fixtures and Limits In-circuit test is the workhorse of assembled board testing. It checks the board as a collection of components and connections rather than as a working product, which means it can find a wrong value or a missing part before anyone powers the design…

X-Ray Inspection of PCB Assemblies: What It Finds Once a ball grid array is reflowed, nobody can see the joints underneath it. X-ray inspection is the standard answer, and it is also one of the most misunderstood processes in electronics manufacturing, because the image shows density rather than geometry and…

Solder Mask Clearance: Rules, Dams and Vias Solder mask clearance is the gap between a pad and the edge of the mask opening around it, and it is one of the few layout parameters that is decided by the assembly process rather than by the circuit. Get it right and…