接觸熱阻對高功率固態雷射系統散熱之影響

Abstract

在固態雷射系統中，雷射晶體與散熱冷板貼合間必須有一緩衝層(Buffer)存在，而此緩衝層有共有兩種功用，第一點為吸收雷射晶體與散熱冷板因熱而膨脹的體積，第二點為降低貼面間的接觸熱阻，隨著固態雷射的功率越來越大，有效降低接觸熱阻變得相當重要，使得熱能夠被導出。 本論文為量測使用於雷射系統的熱介面材料之接觸熱阻，並且要能有效的降低接觸熱阻，此量測實驗為符合ASTM D5470-12規範，而本研究中共量測兩種形式之接觸熱阻，第一種為量測單一緩衝層之接觸熱阻，緩衝層材料共有四種，分別為銅、鉛、錫和銦之軟金屬，此四種材料的接觸熱阻皆會因壓力上升而下降，而銦的接觸熱阻為四種材料中最低者，在最大壓力時其接觸熱阻為0.076 (℃∙cm^2/W)，第二種則為緩衝層上下貼合面皆加上新設計低熔點合金(Low melting temperature alloy, LMTA)的改良設計，此新設計LMTA可解決低熔點合金溢出之問題，且在這樣的搭配之下，接觸熱阻已不受壓力所影響，且能有效的將接觸熱阻降低40-95%，效果非常的顯著，而在此實驗中的接觸界面溫度需高於80℃，以符合雷射系統運作時之界面溫度。

In the solid-state laser systems, high power laser slab must be cooled to avoid failure. Normally a buffer layer is incorporated amid laser slab and the cooling cold plate. This buffer layer has two functions, i.e. to absorb the thermal expansion by laser slab and to reduce thermal contact resistance. Since the laser power is quite enormous, hence effective reducing the contact resistance becomes very important. In this thesis, the measurement of thermal contact resistance of thermal interface materials applicable for a solid-state laser system is made available. This experiment complies with ASTM D5470-12 test specifications. In this study, ways to reduce thermal contact resistance are conducted in two different approach. Firstly, the study examines the performance of soft metal buffer layer like copper, lead, tin and indium. Test results indicate that the thermal contact resistance of the tested four soft metal decrease with the rise of contact pressure. It is found that the indium shows the lowest interface contact resistance, and the lowest thermal contact resistance is 0.076 (℃∙cm^2/W) at the highest supplied contact pressure. Secondly, by utilizing a low melting temperature alloy (LMTA) with the upper and lower surface being accompanied with the buffer layer, the contact resistance can be significantly reduced. However, the LMTA may cause additional problem of overflow after melting. To resolve this problem, a new design with indium encircling LMTA is proposed. This design features two outstanding characteristics. The overflow is eliminated and it is quite effective at a very low supplied pressure. In fact, the thermal contact resistance is reduced more than 95%.