Why material selection is a buying decision
Material selection is usually presented as an engineering topic. In 2026 it is equally a commercial one, because laminate is 20 to 50 percent of a bare-board price depending on construction, and its availability now varies by grade in a way that it did not three years ago.
That changes the shape of the decision. In a stable market, the question is which material meets the requirement at the lowest cost. In the current market the question is which material meets the requirement, is available in the quarter the build is scheduled, and has a second source. A grade that is technically ideal but has a sixteen-week lead time is not a solution to a twelve-week schedule.
The pages in this section are grouped by that reality: first the properties that genuinely decide the grade, then the specific families, then the finish and copper decisions, which are cheaper to change and more often over-specified. If the vocabulary is new, the working definition of a PCB is the shorter starting point.
The properties that decide the grade
Four properties do most of the work.
The glass transition temperature, or Tg, describes the point at which the resin softens and the material's dimensional behaviour changes. It matters for boards that see multiple assembly reflows or high operating temperatures. It is also the single most over-specified property in ordinary industrial designs: high-Tg material is frequently specified by habit where thermal analysis would not require it, and in 2026 it carries both a price and an availability premium.
The decomposition temperature, or Td, describes thermal robustness at the upper end and matters for lead-free assembly and for heavy copper constructions where heat is slower to escape.
The dielectric constant and loss tangent, Dk and Df, describe how the material behaves at high frequency. These drive the choice for RF and high-speed digital work, and they are the reason a family of specialised laminates exists alongside FR-4. Below roughly a few hundred megahertz, ordinary FR-4 is usually adequate; above that, the loss rises and the choice becomes consequential.
Comparative tracking index, or CTI, describes resistance to surface tracking under contamination and voltage. It matters for power and industrial boards with high voltage spacing, and it is often the property that actually requires a different material when a design fails a safety test.
Everything else, including flexural strength, water absorption and coefficient of thermal expansion, matters in specific applications rather than generally.
The families
FR-4 is a family of glass-reinforced epoxy laminates meeting a flammability specification, not a single product. Two quotations for FR-4 can differ in Tg, in Dk, in thickness tolerance and in price, and both can be correct. The FR-4 guide covers the grades and how to specify them without ambiguity.
High-Tg laminates are the next step and are appropriate where assembly thermal load or operating temperature justifies them. The high-Tg guide sets out when the extra cost buys something and when it does not.
Polyimide is the standard choice for flexible and rigid-flex constructions, where the requirement is not only temperature but flex endurance and dimensional stability through bending. The polyimide guide covers the material behaviour that matters for flex design.
High-frequency systems, including PTFE-based and ceramic-filled laminates, are a different cost category. The RF materials guide explains the stackup implications, because a high-frequency board is a system of material, copper profile and construction rather than a laminate substitution.
Metal-core and heavy-copper constructions sit outside the laminate question and are covered under board technologies. Their material decision is about thermal path and current, not dielectric performance.
Copper, which is cheaper to get wrong
Copper weight is specified as finished weight per unit area, and it is the most commonly confused number on a fabrication drawing. Starting foil weight and finished weight are different because plating adds copper, and a specification that names one while the supplier measures the other will disagree at inspection.
Two practical rules. Specify the weight the current requires, on the layer that carries it, rather than applying a blanket figure; inner layers at one ounce frequently carry what a design has specified at two. And remember that heavy copper changes the process, not only the material: etching, plating and minimum feature size all behave differently above a few ounces, and a design that assumes fine features on heavy copper will be quoted with a caveat.
Surface finish, the most over-specified decision
Surface finish protects exposed copper and makes it solderable. Four options cover most work.
Hot air solder levelling is inexpensive, forgiving and adequate for through-hole and coarse-pitch assembly. Its weakness is planarity, which matters for fine-pitch components. Lead-free HASL is the standard variant and does not carry gold or nickel exposure.
Electroless nickel immersion gold gives a flat surface and good shelf life, and is the default for fine-pitch assembly and for boards that will be stored or handled before assembly. It carries gold and nickel cost, and it introduces the black-pad failure mode if the process is not controlled.
Immersion tin and immersion silver are cheaper alternatives with their own storage and handling constraints, and OSP is the lowest-cost option where the board will be assembled quickly and stored carefully.
The buying rule is straightforward: specify the finish the assembly process requires, not the finish that sounds most robust. Moving from ENIG to lead-free HASL where the application permits it removes a volatile cost line, and in 2026 that matters more than it did.
How the material question connects to price
Material increases have been selective rather than uniform during 2026. Thin-glass high-end product rose sharply while some thick-glass commodity product was discounted, and prepreg rose more than laminate in the most recent round. The dated record is in the CCL price timeline.
For a buyer, the consequence is that a grade decision is now also a supply decision. Our materials and stackup page describes the information a fabricator needs to quote a construction rather than a guess, and the quotation route will tell you which grades we can confirm for a given delivery window.
If you are at the start of a design, the more valuable exercise is to write down the four deciding properties with the requirement each has to meet. A specification built that way usually lands one grade lower than the default, and is easier to defend when someone asks why.