Application Test engineering for incircuit test.


Reliably high test precision even with fine-pitch and bi-level applications.

You know from experience how demanding the requirements in the fine-pitch and bi-level fields are. However, did you know how fast and efficiently our fine-pitch-fixtures provide you with high-precision solutions? The following customer scenario relating to an ICT fixture solution for double-sided fine-pitch bi-level testing wil act as a demonstration.

The customer's requirements were as follows:

An assembly group with approx. 3,500 test points, a test point diameter of less than 0.5 mm and grid dimensions of below 1 mm was to be contacted from both sides. In addition, the fixture was to be designed for large volume production operations.

A functional test was to be implemented as an additional special feature. This made it necessary to switch off all those probes in the assembly group which were not relevant to this text.

In addition the assembly group was highly sensitive to bending because of the many ball grid arrays which were soldered on.

And finally it had to be necessary to test individual ICs with capacitive sensors (framescan sensors).

And this application is our solution:

In order to achieve long operating life a fine-pitch fixture (rigid needle fixture) was required because with a conventional fixture very small probes would have been used. These would not have provided the necessary robustness and probe strength. In addition the fine-pitch fixture increases the accuracy of the probes because the probes are positioned very densely in the board and also very closely to the PCB. This is necessary on account of the small test pad with a diameter of only 0.5 mm. As the test points and grid dimensions were equally small at both top and bottom, a rigid probe cassette had to be applied on both sides.

It had to be possible to switch off the probes for the functional test. This is why in this case, too, we integrated a bi-level mechanism on both sides (top and bottom).

This enables a two-stage lift of the probes, enabling the functional test to be implemented with longer and shorter probes separately from the in-circuit test and without being influenced by it. In a further stage it was necessary to reduce the bending of the board to an absolute minimum. For this purpose we carried out a simulation of the forces to be applied before implementing the design and used this as a basis for determining the optimum distribution of the areas to be held down.

To achieve this we used simulation software developed especially for us which enables the individual probes and push fingers to be applied as supports in order to calculate the bending and tensions exerted on the board.

Any bending was also to be counteracted mechanically and for this purpose complete push-finger boards in which the components are individually positioned were used instead of individual push fingers.

The special feature of this fixture lay in its comprehensive combination of technologies. We had already constructed double-sided fixtures as well as rigid probe and bi-level fixtures. On the other hand, a combination of double-sided application in the bi-level and rigid probe mode was an absolute first - even for the specialists at ATX.

We integrated the framescan sensors in the rigid probe package so that they can easily be exchanged, and there was plenty of room in the housing for extensive additional hardware.