BÜRKLE: Constant volume flow in PCB production

"At first we were skeptical. And in the end, we probably outdid ourselves," says Markus Haist, Technical Manager of Wolfgang Bott GmbH & Co. KG. When such tones come from a company that is otherwise a master of modesty in the spirit of traditional Swabian hidden champions, there must be something extraordinary behind them.

The reason for the enthusiasm: The hydraulic experts from Mössingen have developed a micro control valve for Bürkle presses, which are used in the production of printed circuit boards. Its task: It regulates the flow of smallest oil quantities drop by drop in a fine and well dosed way to keep the volume flow in the presses constant. The special feature: Not only are the parameters to be controlled tiny, but the dimensions in which the control technology is housed are also very small at 50 mm x 55.5 mm x 90 mm.

The cooperation between the two companies had come about when Bürkle was looking for another supplier for the control technology in its presses within the scope of its Second Source Strategy - and came across the family company Wolfgang Bott. Bott has specialised in the development, production and sale of hydraulic power units, cylinders, control blocks and valve technology as well as systems.

Printed circuit boards require a great deal of sensitivity in terms of pressure and temperature during production. As highest quality is required, Bürkle presses are used worldwide: They convince by accuracy and constancy regarding pressure and temperature, whereby tiny units play a major role.

Printed circuit boards in every product

Bürkle builds presses for the production of multilayers with four tiers up to 24 tiers. The force the presses can generate ranges from 400 kN to 20,000 kN. However, due to the heat input into the plastic circuit boards, the material expands over the pressing period, which can range from 15 minutes to 6 hours depending on the product. If the press would not yield and compensate now, the complete press filling of printed circuit boards would be destroyed. "Our micro flow control valve ensures that this does not happen," assures Haist.

The 2-way micro flow control valve developed by Bott as early as 2016 keeps the set flow rate constant, regardless of the pressure difference across the valve. The orifice plate and pressure compensator are connected in series, with the orifice plate downstream of the pressure compensator. For proper operation, a certain minimum pressure difference must be present at the measuring orifice. The construction with orifice and pressure compensator functions quasi as a throttle. The oil droplets flowing through the valve to compensate for the pressure difference must always have the same quantity of liquid - regardless of whether 100 bar or 300 bar are present in the system. This is set by means of a rotary knob with which the orifice plate can be finely adjusted and which controls the volume flow between 0 l/min and 5 l/min. The setting angle is 270°.

Christoph Müller did not compromise on the compact dimensions. "We did not want to have to change the entire hydraulic block for our systems because of the new flow control valve. This would not have made sense simply because of the spare parts supply alone". The introduction of the valve would also have been enormously delayed. Since the beginning of 2017 the new micro flow control valve from Bott has been installed in the Bürkle presses. And the secret hidden champion did not want to tell that it also fulfils the function of three conventional valves.