I-substrate yebhodi lesifunda le-High Tg lizoshintsha lisuke ku- “state glass” liye ku- “state rubber” lapho izinga lokushisa likhuphukela endaweni ethile, futhi lokhu kushisa kubizwa ngokuthi yi-glass transition tempor (Tg) yebhodi. Ngamanye amagama, i-Tg yisilinganiso sokushisa esiphezulu (℃) lapho i-substrate ihlala iqinile khona. Lokho ukusho ukuthi, izinto ezijwayelekile ze-PCB substrate ezishisa kakhulu azivezi nje ukuthamba, ukusonteka, ukuncibilika nezinye izinto, kepha futhi nokusebenza kwezimpawu zomshini, zikagesi zokwehla okucijile (angicabangi ukuthi sifuna ukubona imikhiqizo yabo ivela lesi simo).

Ngokuvamile, ibhodi Tg ingaphezu 130 degrees, Tg okusezingeni eliphezulu ingaphezu 170 degrees, naphakathi Tg Izinga ezingaphezu kuka-150.
Ngokuvamile i-PCB engu-Tg≥170, ebizwa nge-PCB ephezulu ye-Tg.
Lapho i-Tg ye-substrate inyuka, ukumelana nokushisa kwebhodi lesifunda, ukumelana nomswakama, ukumelana namakhemikhali, ukumelana nokuqina nezinye izici kuzothuthukiswa. Ukuphakama kwenani le-TG, kungcono ukumelana nokushisa kwepuleti. Futhi i-TG ephezulu isetshenziswa kaningi kwinqubo engaholi,
I-High Tg isho ukumelana nokushisa okuphezulu. Ngokuthuthuka okusheshayo komkhakha we-elekthronikhi nemikhiqizo ye-elekthronikhi emelwe yikhompyutha, ukumelana okuphezulu kokushisa kwezinto ze-PCB substrate sekube yisiqinisekiso esibalulekile lapho ukuthuthukiswa kubhekisa ekusebenzeni okuphezulu nakuma-multilayer aphezulu. Ngaphezu kwalokho, ukuvela nokuthuthuka kobuchwepheshe bokufakwa kwabantu obukhulu obumelwe yi-SMT ne-CMT kwenza i-PCB ihlukane ngokwengeziwe ngokusekelwa kokumelana nokushisa okuphezulu kwe-substrate ekuvulekeni okuncane, isifunda esihle nefomu elincanyana.
Ngakho-ke, umehluko phakathi kwe-fr-4 ejwayelekile kanye ne-Tg fr-4 ephezulu ukuthi kusesimweni esishisayo, ikakhulukazi esimweni sokushisa ngemuva kokumunca umswakama. Futhi kukhona umehluko omkhulu emandleni womshini, ukuzinza okulinganayo, ukunamathela, ukumuncwa kwamanzi, ukubola okushisayo, ukwanda okushisayo nezinye izimo zezinto zokwakha. Imikhiqizo ene-Tg ephezulu ngokusobala ingcono kunezinto ezijwayelekile ze-PCB substrate. Eminyakeni yamuva, inani lamakhasimende adinga ukukhiqizwa kwebhodi lesifunda ephezulu le-Tg lenyuke unyaka nonyaka.