Layer to Layer Registration in Multilayer PCB Every layer in a multilayer board has to line up with every other layer, and the alignment is built up from a series of steps that each contribute error. The total is what decides whether an inner layer pad still covers the hole…

Test Strategy: Combining AOI, X-ray, ICT and Functional Test No single test finds every defect, and every test adds cost. The engineering question is not which method is best but which combination covers the failure modes of this product at an acceptable cost. Answering it requires knowing what each method…

Component Lead Coplanarity and Placement Control Coplanarity is the distance between the lowest and the highest lead of a component when it rests on a flat surface. A lead that is out of plane does not touch its pad, and no amount of paste will bridge the gap. How It…

Test Coverage and Yield Balance Test coverage and yield balance describe the same tension from two directions. Coverage is what the test programme can detect; balance is whether the effort spent detecting it matches the risk of missing it. A line with heavy inspection and light process control will report…

Control Plan Development for PCB Assembly A control plan is the document that says which parameters matter, how they are monitored and what happens when they drift. It is required by automotive and medical customers, and it is useful everywhere else, because it forces a production line to decide in…

ESD Control Audit and Measurement Practice An electrostatic discharge control programme is a set of measurements, and a programme that is not measured is a set of objects that were purchased. The audit is what keeps the wrist straps, the benches and the flooring in the condition the programme assumes.…

Static Damage Prevention in Bare Board Handling Guide A bare board looks like a passive object, and it is often handled with less care than an assembled one. In fact a static discharge can damage a thin dielectric, a fine trace or a plated hole, and the damage may be…

Castellated Hole: Preparation, Placement and Process Control A castellated hole is a plated hole that has been cut in half so that the plating is exposed on the board edge. It lets a small module be soldered onto a carrier board like a component, with connections on the side rather…

Conformal Coating Thickness Measurement Methods Conformal coating is applied to a defined thickness, and the thickness is the parameter that decides how long the coating protects. Measuring it on a curved assembly is harder than it sounds, and the method chosen decides what figure is being reported. Why the Thickness…

Nitrogen Reflow Compared With Air Reflow Reflowing in nitrogen is one of those process choices that is either essential or pointless depending on the product. Nitrogen suppresses the oxidation that competes with wetting, which helps when the surfaces are marginally solderable, when the pitch is fine or when the alloy…