锗-硼硅玻璃局部加热低温封接温度场研究

在光学读出非制冷红外热像仪焦平面阵列(FPA,Focal Plane Array)真空封装结构中,硼硅玻璃和双面镀增透膜的锗片分别作为透可见光和透红外光的窗口材料.由于锗窗上增透膜不能承受高温(<250℃),同时FPA也不能承受高温(<100℃),因此封装过程须在低温下进行,并对锗窗上的增透膜及FPA进行保护.本文提出了一种用于锗-硼硅玻璃低温扩散焊接的局部加热方法.该方法从导热系数较大的锗窗外表面加热(200℃),而导热系数较小的硼硅玻璃窗口外表面维持低温(60℃).有限元模拟计算结果表明,该加热过程稳态情况下待焊接区域温度约200℃,满足低温焊接的温度要求.锗窗上温度(200℃)低于250℃,且FPA区域的温升在75℃以下.用实验方法对模拟结果进行了验证,实验结果同模拟结果一致,证明该方法能够有效地保护FPA及锗窗上的增透膜.

On the Temperature Distribution in Localized Heating for Low Temperature Sealing of Germanium-Borosilicate Glass

In FPA (Focal Plane Array)vacuum packaging of the optical readout uncooled infrared imaging system, Germanium glass with antireflection coatings on both sides and Borosilicate glass are used as the windows for transmitting infrared light and visible light, respectively. Due to the temperature limitation of the antireflection coatings on Germanium glass (<250℃) and FPA (<100℃), the packaging process has to be conducted at low temperature, and thermal protection for FPA and antireflection coatings on Germanium glass must be designed correspondingly. This paper proposes a localized heating method for Germanium-Borosilicate Glass low temperature diffusion bonding. In the present method, Germanium window which has higher thermal conductivity is heated up from its outer surface (200℃), while the temperature at the outer surface of Borosilicate Glass with lower thermal conductivity is kept lower (60℃). Finite element simulation results indicate that temperature increase is relatively high in bonding region (200℃), satisfying the requirement of low temperature bonding, while the temperature of Germanium keeps below 250℃; moreover, the temperature increase in FPA region is relatively low (below 75℃). Meanwhile, simulation results are consistent with experimental measurement. Therefore, FPA and the antireflection coatings on Germanium can be protected effectively by proposed heating method.