Ultra thermal stability of LED die-attach achieved by pressureless Ag stress-migration bonding at low temperature
Ultra thermal stability of LED die-attach achieved by pressureless Ag stress-migration bonding at low temperature
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DOI：
10.1016/j.actamat.2015.02.011
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发表时间：
2015-05-01
期刊：
影响因子：
9.4
通讯作者：
Suganuma, Katsuaki
中科院分区：
文献类型：
--
作者：
Kunimune, Teppei;Kuramoto, Masafumi;Suganuma, Katsuaki
利用最新开发的银应力迁移键合(SMB)技术，发光二极管(LED)管芯可以在200℃以上的空气中无压力地粘合在玻璃基板上，其中芯片和基板表面都覆盖了几微米厚的银层。我们研究了这种新兴的贴片方法，并揭示了详细的键合过程。银涂层中的热残余应力在两个表面上都形成了丘状，挤压出来的银颗粒填充了接触表面之间的缝隙。在不施加任何压力的情况下，可以在大的粘合区域上实现良好的接触。然而，LED管芯暴露在较高的工作温度下可能会增加键合界面结构中形成空洞的风险，从而由于键合强度下降而导致裂纹或界面失效。在这项研究中，我们在银键层下插入一层高熔点金属如铂或Ru的阻挡层，以防止从银层中的空穴扩散。因此，即使在440℃下保温2小时，Ag SMB也不会受到热暴露测试的影响，从而确保LED芯片贴片的使用寿命足够长。因此，除了银的理想反射率和电/热传导性外，我们的无压银SMB方法还实现了优异的热稳定性，非常适合LED应用，以及各种其他高温宽带隙功率半导体的功率器件，如GaN和碳化硅。(C)2015 Acta Materialia Inc.由爱思唯尔有限公司出版。版权所有。
Using recently-developed Ag stress-migration bonding (SMB), a light-emitting diode (LED) die can be bonded on a glass substrate above 200 degrees C in air without pressure, where both the die and substrate surfaces are coated with a few-microns-thick Ag layer. We investigate this emerging die-attach method and reveal the detailed bonding processes. The thermal residual stress in the Ag coating layer causes hillock formation on both the surfaces, and the extruded Ag grains grow to fill the gap between the contacted surfaces. A sound contact over the large bonded area can be achieved without applying any pressure. However, the LED dies exposed to a high working temperature may increase the risk of void formation in the bonding interface structure, leading to a crack or interface failure due to the bond strength degradation. In this study, we insert a barrier layer of a high melting-point metal like Pt or Ru under the Ag bond layer to prevent void diffusion from the Ag layer. The high bond strength achieved by Ag SMB is then unaffected by the heat exposure tests even at 440 degrees C for 2 h, assuring sufficiently long lifetime for the LED die-attach. Our pressureless Ag SMB method thus achieves excellent thermal stability, in addition to the ideal reflectivity and electric/heat conductivities of Ag, perfectly suitable for LED applications, as well as various other power devices of high-temperature wide-bandgap power semiconductors like GaN and SiC. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.