Tg test method and influencing factors

PCBs made of high-Tg plates perform better than ordinary Tg and medium-Tg PCBs in terms of stability and reliability. 

(1) High heat resistance: Reduce the warpage due to temperature, which can reduce the warpage of the pad during hot melt welding and thermal shock of PCB. 

(2) Low coefficient of thermal expansion (low CTE), to reduce copper cracks in hole corners due to thermal expansion, especially in PCB layers of eight layers and above, the reliability of plated through holes is better than that of ordinary Tg PCB boards. 

(3) It has excellent chemical resistance, and its performance is still better under the immersion of many chemical liquids in the wet process.

2.1. Effect of Tg value on PCB

The Tg value obtained in the DSC and DMA tests reflects the degree of curing of the sheet resin. The larger the Tg value, the lower the degree of crosslinking reaction between the polymer molecules and the more polar groups present in the sheet Therefore, the sheet material is very easy to absorb water. The potential defects in this pressure plate increase with time. The more the PCB board absorbs water, the hot plate test often occurs when the customer does a thermal shock test, which leads to serious reliability problems. The larger the △Tg value, the larger the hole thickness, copper throwing, and the quality of the plated through hole in the drilling process. The insufficient thermal expansion of the cured resin changes and the hole corner breakage is easy to occur.