Feature: Interconnections Figure 1: Flip-chip bonding
Quaphically patterned
By Daniel Schultze, Managing Director, Tresky
Microelectronics wins with optimised die bonding processes
W
hen it comes to microprocessors, microcontollers and system-on- chip ICs, everyone quickly learns of their advances and technological progress. However, their packaging, interconnections, bonding and
soldering also move on, despite the lack of wide interest. For example, with the die-to-die bonding process called “thermosonic bonding”, thermocompression bonding is combined with ultrasonic welding during the bonding process, for achieving the best of both worlds. Originally, thermosonic bonding (TSB) was mainly used in
wire bonding. But, now, by combining the bonding process with ultrasonic soldering, the process reduces both the bonding pressure and the required temperature, which is very beneficial in semiconductor manufacturing: the two processes can be used for flip-chip bonding, for example. The solderless die-to-die bonding technology for large-
area array connections allows an array of gold bumps on the bottom of an IC to be connected to gold-plated pads on a substrate. Thermocompression bonding is often used for this simple, clean and dry assembly process, but it usually requires interfacial temperatures above 300°C, which can damage
34 May 2023
www.electronicsworld.co.uk
packaging materials, foils and sensitive ICs. If, on the other hand, flip-chip bonding is combined with ultrasonic welding, it is possible to reduce the interfacial temperature between 100 and 160°C and the bonding force between 20 and 50g/bump.
The thermosonic bonding process The TSB process starts with a substrate placed on a heated pad and held in position by vacuum, with the pick-and-place tool holding the chip with a die collet designed for thermosonic bonding applications. Here at Tresky we have a pattern- recognition system that aligns the chip with the substrate, to precisely connect the gold stud bumps to it. Once the required adhesion force is achieved, the current
of ultrasonic soldering is applied for a defined period of time. The parameters relevant for ultrasonic soldering, such as power, time and delays, can be defined individually for each process using our software. The coplanarity and parallelism of the die collet in relation to the substrate are important parameters for achieving a good joint. Incorrect alignment can lead to uneven force distribution, which in turn creates an insufficient bond with the surface. Tresky’s vertical technology guarantees stable and accurate coplanarity and parallelism over the entire z-axis stroke,
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