Thermomechanical Reliability of Low-Temperature Sintered Attachments on Direct Bonded Aluminum (DBA) Substrate for High-Temperature Electronics Packaging

This study focused on the development and evaluation of die-attach material and substrate technology for high-temperature applications. For the die-attach material, a low-temperature sintering technique enabled by a nanoscale silver paste was developed for attaching large-area (>100 mm2) semiconductor chips. The nanoscale silver paste can be sintered at a much lower temperature (<300 oC) than in the conventional sintering process (>800 oC), and at the same time reached about 80 vol% bulk density. Analyses of the sintered joints by scanning acoustic imaging and electron microscopy showed that the attachment layer had a uniform microstructure with micron-sized porosity with the potential for high reliability under high temperature applications. We also investigated the effects of a large temperature cycling range on the reliability of direct bonded aluminum (DBA) substrate. DBA substrates with different metallization were thermally cycled between -55 oC and 250 oC. Unlike with the DBC substrate, no delamination of aluminum from the aluminum nitride ceramic base-plate was observed for the DBA substrates. However, aluminum surface became roughened during the thermal cycling test. It was believed that in the high-temperature regime, the significant amount of thermomechanical stress and grain-scale deformation would cause recrystallization and grain-boundary sliding in the aluminum layer, which would further lead to the observed increase in surface roughness. The influence of metallization over the aluminum surface on the extent of surface roughness was also characterized. In addition to evaluating the reliability of nanoscale silver paste and DBA substrate individually, this work also conducted experiments that characterize the compatibility of nanoscale silver paste on DBA substrate in terms of reliability in a high-temperature environment. In the large-area attachment, the sintered silver was found to be very compliant with the deformed aluminum. The device-to-silver and silver-to-substrate interfaces remain intact after up to 800 cycles. No large scale delamination and horizontal cracks were observed. However, some vertical crack lines began to show after certain number of cycles. It was believed that these vertical cracks were caused by the thermomechanical stresses in the sintered silver layer. In addition, with regard to the thermal performance, since most of the heat was generated from the semiconductor devices and were transferred vertically through the die-attach material to substrate, these vertical cracks were also considered more advantageous than horizontal cracks.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Materials Science and Engineering

Department dc:contributor.department

Materials Science and Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2010

Author dc:creator

• Lei, Guangyin

Chair dc:contributor.committeechair

• Lu, Guo-Quan

Committee members dc:contributor.committeemember

• Aning, Alexander O.
• Ngo, Khai D. T.
• Suchicital, Carlos T. A.
• Guido, Louis J.

• Nanoscale silver paste
• low-temperature sintering
• direct bonded aluminum (DBA)
• thermomechanical reliability
• high-temperature electronics
• temperature cycling reliability

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-05132010-174237

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/37803