Copper Foil Types for PCB Laminates The copper on a board is supplied as a foil that is laminated to the dielectric, and there are two families of foil with different manufacturing routes and different properties. One is rolled from a cast ingot and the other is electrodeposited onto a…

Resin Content Control in Laminates Resin content is the fraction of a laminate that is not glass fabric, expressed as a percentage by weight or by volume. It sounds like a manufacturing detail, but it is the variable that sets the effective dielectric constant, the flow during lamination, the finished…

Stencil Aperture Home Plate Design for Fine Pitch Printing A stencil aperture is a hole through which paste is pushed, and its shape decides how much paste is deposited and how cleanly the deposit releases from the walls. For most components the aperture is a straightforward rectangle slightly smaller than…

Glass Fabric Effect on PCB Properties A glass reinforced laminate is a composite of glass fabric and resin, and the fabric is not a passive filler. The style of the weave, the thickness of the yarn and the proportion of resin determine the dielectric constant, the mechanical stiffness, the drilling…

Low Loss Laminate Selection A low loss laminate is chosen when the insertion loss of a channel has become the limit on the design. The loss comes from the dielectric and from the copper, and the two contributions have different frequency behaviour and different remedies. Selecting a material without separating…

Rogers Material Guide for High Frequency Boards Rogers is a brand name that has become a shorthand for the family of laminates used in high frequency and microwave work. The family covers several chemistries, from a soft polytetrafluoroethylene to a ceramic filled composite and a thermoset material, and they are…

Halogen Free Laminate Guide A halogen free laminate avoids the brominated flame retardant that has been the standard in glass reinforced epoxy for decades. The change was made for environmental and regulatory reasons, and it is not a cosmetic substitution: a different chemistry is used to achieve the same flame…

Via Stub Effects and Back Drilling at High Frequency A via that connects two layers also connects to every layer below, whether those layers need the connection or not. The unused portion is a stub, and at high frequency it behaves like a small antenna attached to the signal path.…

High Tg Material Selection Guide A high tg laminate is one whose glass transition temperature is well above the ordinary range. Above that temperature the resin stops behaving as a glass and becomes more compliant, so its expansion rises sharply and its mechanical stiffness falls. A material with a higher…

Annular Ring Requirements For Plated Holes The annular ring is the width of copper that surrounds a drilled hole on the pad. It is the material that connects the plated barrel to the conductor on that layer, and it is the part of the pad that has to survive drilling,…