Generally speaking, there are two kinds of resins purchased by the board manufacturer, one is ordinary PC resin, and the other is PC resin with anti-ultraviolet additives. The selected anti-ultraviolet additives are as large as the following categories:
(1) Salicylic acid esters, such as p-tert-butylphenyl salicylate (TBS).
(2) Benzophenones, such as 2-hydroxy-4-methoxybenzophenone (UV-9); 2-hydroxy-4-methoxy-2'-carboxybenzophenone (UV- 207); 2-hydroxy-4-n-octyloxybenzophenone (UV-531).
(3) Benzotriazoles such as 2-(2'-hydroxy)-3,7,5'-di-tert-butylphenylbenzotriazole (UV-320); 2-(2'-hydroxy-5 '-Tert-octylphenyl)benzotriazole (uV-5411) and so on. PC board is very easy to produce internal stress. Whether the board has internal stress can be tested by carbon tetrachloride soaking and polarized light. The internal stress of the sheet can be eliminated by annealing.
