Our own Jörg Kiesewetter, Ken Smith, and Eric Hill recently teamed up with imec’s Erik Jan Marinissen, Ferenc Fodor, and Bart De Wachter to co-author an article in Chip Scale Review titled Evaluation of Advanced Probe Cards for Large-Array Fine-Pitch Micro-Bumps. Vertical stacking multi-die assemblies are a cost-effective way to keep up with Moore’s Law but testing them requires wafer probing on fine-pitch micro-bumps, not an easy task and one considered impossible until recently.

With the arrival of advanced MEMS-type probe cards, their large fine-pitch probe arrays match the micro-bumps making wafer probing possible. The article dives into the process and results of the evaluation of these advanced probe cards at imec. To do this, the authors manufactured dedicated micro-bump test wafers and developed and installed inside imec’s 300mm Fab-2 clean room a new test system with dedicated hardware and software that included:

  • Test instrumentation including a digital multi-meter and a wide switch matrix
  • Hard docking test head with manipulator that connects through an interface with spring-loaded contacts to
  • An advanced MEMS-type probe card, which is placed in
  • A fully-automatic probe station with wafer loader; the system complemented with
  • In house developed software for automatic test generation and result data visualization and analysis

The testing yielded a lot of data, which can be seen in the article, but the authors summarized the results as follows:

Probe cards are consumables with a limited number of touchdowns. The advanced FormFactor Pyramid Probe® RBI probe cores are not inexpensive, so every touchdown adds cost. However, comparisons with the cost analysis tool 3D-COSTAR from TU Delft and imec revealed that using these expensive advanced probe cards to probe on microbumps is still significantly cheaper than its alternative: providing a limited number of large, easy-to-probe pre-bond probe pads, as this will increase the test time significantly and still leaves the micro-bumps untested.

To download the article and details of the evaluation, click here.