Drill Registration and Its Effect on Pads What Registration Means Registration is the positional agreement between the drilled hole and the copper pattern it has to connect to, measured on each layer. It is not a single number. The hole has to align with the inner-layer pad, with the outer-layer…

Plating Adhesion and Resist Adhesion Problems Two Interfaces Most adhesion problems on a circuit board occur at one of two interfaces: between the copper and the laminate, and between a coating and the copper. The first is created during lamination, when the resin flows against a treated foil and then…

Rework and Repair: Limits and Documentation What Rework Covers Rework is the correction of a defect to bring an assembly into conformance, and repair is the restoration of a functional assembly that has failed. In practice the two are treated together, because they use the same tools and carry the…

Insertion Loss Budgets for PCB Channels What Insertion Loss Includes Insertion loss is the reduction in signal power between the transmitter and the receiver, expressed in decibels as a function of frequency. In a board channel it is the sum of several contributions: the dielectric absorption of the laminate, the…

AOI Programming and Escape Prevention What AOI Does An automated optical inspection system photographs the board after reflow and compares what it sees with a reference, using a mixture of image processing and measurements to decide whether each component and joint is acceptable. It finds missing parts, reversed parts, shifted…

Laser-Cut Versus Electroformed Stencils How a Stencil Is Made A stencil is a thin metal sheet with apertures through which paste is printed onto the pads. Two processes dominate: laser cutting, in which each aperture is cut from a rolled stainless sheet, and electroforming, in which the sheet is grown…

Clock Trace Routing: Length and Termination Why a Clock Is Different A clock is a periodic signal that runs at a single frequency, and that changes how it behaves compared with a data line. Its energy is concentrated at the fundamental and its harmonics rather than spread over a band,…

Decoupling Capacitor Placement and Loop Area What Decoupling Does A decoupling capacitor is a local reservoir of charge that supplies a switching device while the power distribution network is still responding. When a logic gate switches, it draws a current pulse in a few hundred picoseconds, and the inductance of…

Burn-In and Aging Tests for Assemblies What an Aging Test Screens Every population of manufactured assemblies contains a small number of units with a latent defect that will fail early. The distribution of failures over time follows a curve with three regions: a decreasing failure rate at the start, caused…

Incoming Inspection of Bare Boards Why Inspect on Receipt An incoming inspection is the last opportunity to reject a board before value is added to it. Once components are placed and reflowed, a fault that came from the bare board is indistinguishable from an assembly fault until a considerable amount…