Who makes Low-Dk glass cloth for AI data centers

Laminate is resin reinforced with woven glass cloth. The cloth gives the board its stiffness and dimensional stability, and it also sets a large part of the board's electrical behaviour, because glass and resin have different dielectric constants and a signal crossing the weave sees an alternating pattern. Low-Dk glass grades exist to narrow that mismatch, along with flattened and spread weaves that make the pattern less pronounced. The effect this fixes is real and hard to design around. On a high-speed differential pair, one trace can run over glass bundles while its partner runs over resin, and the resulting skew shows up as closed eyes at the receiver. At lower rates it is a nuisance; at the rates an AI switch or accelerator board runs, it is a design constraint that decides which laminate is qualified. Demand here follows layer count and lane rate rather than board area, and it concentrates on a small number of specialty glass grades made by a short list of Japanese producers, several of whom sell into the same laminate makers. What to look for is which glass grade a laminate is built on rather than the laminate brand, and whether a supplier has capacity in the specialty grades specifically — general glass-cloth capacity does not substitute, and adding a furnace for these is a long project.