FR4 vs Rogers for RF Modules Why the Laminate Decides RF Performance At low frequency the copper does the work and the dielectric is a mechanical support. At radio frequency the dielectric becomes part of the circuit. Its permittivity sets the impedance of every trace and the physical length of…

Any-Layer HDI PCB: Design and Manufacture What Any-Layer Means In an ordinary multilayer board a via passes through the whole stack, and in an HDI board with a single build-up layer the microvias reach only the next layer. Any-layer HDI, sometimes called every-layer interconnection, goes further: a microvia can be…

Solder Beading and Solder Ball Defects Two Different Defects Solder balls and solder beading are usually lumped together and should not be. A solder ball is a small sphere of alloy sitting on the surface, often on or beside a solder mask feature, and it is a contamination and short-circuit…

Conductive Anodic Filament: CAF Failure Explained What CAF Is Conductive anodic filament is a copper-containing path that grows inside the laminate along the resin and glass interface, from an anode toward a cathode, while the board is under bias in a humid environment. It is not a surface phenomenon and…

Selective Soldering: Process and Design Rules Why Selective Soldering Exists Modern boards are mostly surface mount, but they almost always carry a few through-hole parts: connectors that must survive insertion force, transformers, relays, power terminals and parts that are simply cheaper in a leaded package. Those joints still have to…

Reflow Profile Design for Mixed Assemblies What the Profile Actually Controls A reflow profile is the temperature the assembly experiences against time, and it does three jobs at once. It has to bring every joint to a temperature above the melting point of the alloy for long enough that the…

Solder Mask Slivers: Causes and Design Fixes What a Sliver Is A sliver is a narrow strip of solder mask that is not fully supported by the board surface, either because it is thinner than intended or because it sits between two openings that leave it barely attached. In its…

Inner Layer Registration: Control and Measurement <h2 Why Registration Is the Hardest Tolerance Every layer of a multilayer board is imaged separately and then bonded together in a press, and the alignment between them is the result of a chain of errors that starts with the artwork and ends with…

Nailheading in PCB Drilling: Causes and Limits What Nailheading Is When the drill passes through an inner layer pad, the copper there is thin and ductile and the laminate around it is comparatively soft. If the drill pushes rather than cuts, the copper is deformed outwards and downwards into the…

PCB Breakaway Tab Design for Depanelling What a Tab Has to Do A breakaway tab is the small bridge of material left between a board and its neighbour or the panel rail when the rest of the outline has been routed away. It holds the board in place through assembly…