Novel Low Temperature and Low Pressure Sintering of ADAS Radar Sensor Antenna Stack

A low temperature and low pressure sintering of antenna stacks with the promising prospect of achieving a single step bonding process of multi-layer wave guide antennas for automotive radar sensors is demonstrated. Silver nanoparticles (Ag-NP) paste with the ability to sinter at 200°C in air allows for easy integration into standard surface mount device reflow process. The paste drying and sintering process of the Ag-NP paste is first optimized using dummy test chips to reduce the typical voiding and channeling in the interconnect when sintered without pressure. In especially, a slow ramp rate with an integrated pre-drying step is applied after placement of the test chips into the wet paste. Afterwards, the process is transferred to the antenna. However, pre-existing bending in the large antenna layers challenges the sintering process without pressure, e.g. larger amounts of paste need to be applied for compensation of the bending. Therefore, the use of a low bonding force in observed to improve the quality of the sintered interfaces. Near bulk like Ag sintered interconnects were realized.