Better fixturing solutions

To reduce the pressures exerted on a PCB, the first and simplest solution is to reduce the probes' forces whenever possible. Secondly, the positioning of the fingers/stoppers must be optimized to control the probe forces, but this is often very difficult to achieve. Mechanically, the stoppers must be located exactly under the pressure fingers to avoid the creation of shear points (Image 5).

The density of the components on both sides of the PCBs often makes it impossible to obey this rule. It is then necessary to eliminate the fingers/stoppers by using contact surfaces that will maximize the support points.

In  addition  to  supporting  the  PCB  perfectly  by  eliminating  a  large  part  of  the deformations, the Push Plate method (Image 6) has the advantage of significantly improving the precision of the assembly. The probes are guided to their contact point with no possibility of deviation. However, it is necessary to clear all the components to avoid any possibility of contact between the pressure plate and the components. Since component positioning tolerances vary from one manufacturer to another, some conflicts can still arise between components and the pressure plate, even though free space was cleared in the cavities. To minimize this possibility, we therefore use a combination of the two methods.

This Pressure Islands method (Image 7) represents the perfect compromise between the standard method and pressure plates. The PCB is perfectly supported thanks to pressure islands in the high-deformation zones identified with our FDS tool and supported with fingers/stoppers where there is enough space. This method has shown excellent results.