VOIDLESS at line speed: Minimizing Voids with Piezo technology

The trend in reducing the size of power components is unstoppable. As a result of this, and in order to achieve reproducible soldering results at the highest quality level, the loss-free heat conductivity of the solder joints in the SMT process takes on ever more importance.

Ersa HOTFLOW 3/20 VOIDLESS — With the Ersa Hotflow 3/20 VOIDLESS, Ersa presents a process efficient solution to minimize the occurrence of voids, which is characterized by its high throughput in inline operation, short process times and low operating costs. The VOIDLESS module, for which no additional maintenance is required and which can be activated /deactivated at any time, reduces the occurrence of voids, when compared to other soldering processes, by up to 98%

After the reflow process, voids may be present in the joints which will hinder the effective thermal transfer, thus possibly causing thermal damages to the power components – right up to the complete failure of an assembly. To counter this issue, Ersa has developed, with its VOIDLESS feature, a new method which will reduce the formation of voids during the soldering process down to a bare minimum. The VOIDLESS module is installed as an addition in the peak zone of an Ersa Hotflow 3/20 reflow system, ensuring that sufficient thermal energy is available for the solder to reach the temperatures required to form solder joints at high mass components.

X-ray images show the differences: The right QFN component, soldered with the VOIDLESS feature activated, shows almost no voids. On the image on the left – processed without the VOIDLESS feature – a large number of voids are clearly visible

Universal method to reduce voids

How did VOIDLESS come about? Already during the year 2012, Ersa was looking for alternative processes to reduce the occurrence of voids in solder joints. In cooperation with the Fraunhofer Institute for Silicate Research (ISC), an organization highly competent and with many years of experience in the field of adaptronic, a feasibility study was undertaken to validate some of Ersa’s preliminary theoretical considerations with the view on their practical implementation. The development centers around a universal method to minimize voids in the liquid solder between the PCB and the components by a sinusoidal actuation of the PCB substrate, whereby primarily a longitudinal wave with an amplitude of a few µm is actuated on the level of the printed circuit board – independent of the PCB geometry. The low starting frequency of the sweep stimulation ensures a gentle, homogeneous propagation of the vibrations in the PCB, without damaging the molecule chains (e.g. in FR 4).

The intensification of the frequency causes a stiffening of the PCB substrate, an increase in the elastic modulus and, because of the reduced damping factor, an improved energy transmission of the liquid solder. Thus, areas with low density, so called “voids”, are literarily “vibrated” out of the solder joint. As such, the liquid solder is stimulated repeatedly by the vibration propagation in a relative shearing motion leading to the observed reduction of voids in the solder joints. Numerous tests performed at the Fraunhofer ISC have proven the high-degree damping effect of molten solder, which prevents damage to the components.

With VOIDLESS: a void rate of less than 2%

The Hotflow 3/20 VOIDLESS combines the established and well trusted Ersa reflow technology with the innovative and patented VOIDLESS optional feature, which can be simply turned off and on if so required, and which offers our customers the highest degree of flexibility in their production process. Compared to the standard reflow soldering processes, a few seconds only are required to reduce the void rate by up to 98%.

Additional positive side effects of the sweep stimulation are the centering of the components on the pad and the optimized spreading of the solder. Delamination of the substrate or the popcorn effect of component bodies do not occur during the Ersa VOIDLESS process. And no additional specifications concerning components or MSL are needed, as they are for alternative processes.