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Content archived on 2024-04-19



The improved microcontact technology forms a small cap intermetallic bonding layer in a metallurgical system, consisting of a high melting metal contact metallization and a low melting metal introduced as thin film deposit or preform foil.

The newly developed joining technique uses process parameters of temperature and time in the range of the conventional reflow soldering. Additionally pressure is applied, bringing the surfaces in tight contact so that diffusion can start. The high melting metal diffuses in the liquid intermediate layer forming a well defined intermetallic phase under solidification. The high melting temperatures of the intermetallic phases are leading to a heat-resistant bond with a low homologous working temperature T/Tm.

For the first time a technology based on the low-temperature solidification of intermetallic phases has been applied to industrial demonstrators, such as die-attach, signal contact, power electronics contact and sensor mounting using different materials such as Si, GaAs, ceramics, FR4, polyimide and Cu. The achieved bond strength is 26.5 Mpa at room temperature and still 17 Mpa at 250 C. The die-attach demonstrators fulfill the requirements of MIL-STD 883D, method 2019.5. Thus the mechanical properties of the IMMICO bond are comparable to standard Au/Su soldering but with a much higher working temperature. Therefore a new test, the hot die shear strength test, was introduced working at a temperature of 250 C. An attached area of 95% could be achieved with small GaAs-dice, determined by Scanning Acoustic Microscopy. The reliability investigations show no significant microstructure degradation, only the layer thickness of the high melting metal should be sufficient because the total consumption of this layer during thermal load may cause a weak interface. FEM simulations show that the mismatch in the thermal expansion of materials in the assembly is limiting the maximum size of the bond area.
Electrical contacts and thermal or mechanical interconnects are frequently the weak links in electronic components and assemblies. Conventional contact technologies such as soft-soldering and adhesive bonding present difficulties in manufacturing and limit the applicability of the systems. The main objective of this Project is to improve electronic components and assemblies by introducing a new and more effective microcontact technology, based on the low-temperature solidification of intermetallic phases which form heat-resistant die-attach as well as signal and power electric contacts. Based on the liquid / solid transition in a thin film metallization, a small gap contact will be formed in the same ranges of temperature and time as used in conventional reflow solder processes. The contacts can withstand a much higher temperature than conventional ones.

The new microcontact technology will be optimised by investigating microscopic defects arising out of contact formation and failures due to mechanical, chemical and thermal loading of the new constructions.

Finally, a test line will be established for industrial verification and dissemination of the new technology.

The increased technical specification of this new technology will result in extensive use of microelectronic systems in many industrial sectors.

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Alcatel Espace SA
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26 avenue J F Champollion
31037 Toulouse

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