Traditional FR4 is no longer enough for today's high-performance circuit boards. Therefore, various resins are mixed with the original epoxy resin to improve the various properties of the substrate. A. Novolac was first introduced as phenolic resin. One of them is called Novolac. The ester formed by Novolac and epichlorohydrin is called Epoxy Novolacs. Mixing this polymer with FR4 resin can greatly improve its water resistance, chemical resistance and dimensional stability. The Tg also increases. The disadvantage is that the hardness and brittleness of the phenolic resin itself are very high and it is easy to drill. In addition, the chemical resistance is enhanced, and the smear caused by drilling is not easy to remove, which causes the multi-layer PTH. Difficulties in the manufacturing process. B. Tetrafunctional Epoxy Another type that is often added to FR4 is the so-called Tetrafunctional Epoxy Resin. It differs from the traditional “bifunctional” epoxy resin in that it has three-dimensional space bridging. High Tg can withstand poor thermal environment, and solvent resistance, chemical resistance, moisture resistance and dimensional stability are much better, and there will be no shortcomings like Novolac. It was first introduced by a substrate factory called Polyclad in the United States. Four functions compared with Novolac, there is another advantage that it has better uniform mixing. In order to keep the multi-layer board easy to remove the scum, this four-function substrate is best baked in an oven at 160 ℃ for 2-4 hours after drilling, so that the resin exposed on the hole wall will oxidize, and the oxidized resin It is easier to be eroded away, and it also increases the resin for further bridging polymerization, which is also helpful to the subsequent manufacturing process. Because of the brittleness, special attention should be paid to drilling. Neither of the above-mentioned added resins can be brominated, so adding general FR4 will reduce its flame retardancy.