Easy and flexible PCB panel testing
Anyone who works with panel testing will be familiar with the long list of associated challenges: difficult and time-consuming panel definition, increasing complexity in fixture construction, including complicated fixture wiring, and complex test program debugging. In addition, mixed panels and associated testing can usually only be generated manually and with a great deal of effort. In production, the panel test often turns into a bottleneck, which limits the overall production speed.
Obviously defective individual circuits are difficult or even impossible to exclude from the test. In addition, there is a high level of rejects, since faults can often only be assigned to the entire panel, but not to the individual board. Testing individual circuits – for example in the case of field returns- is another difficulty, as well as lacking traceability possibilities. However, now different software tools are bringing about useful solutions:
Panel definition made easy
Before you can test hardware on the panel, you face the challenge of defining a panel. What PCB should be positioned where and how? Previously, this was tedious manual work. With the C-LINK DTM software solution from Digitaltest classic CAD formats can now be imported into a panel generator. Individual circuits can then simply be assigned on the panel with a mouse click. Rotations of 0.1-degree increments, mirroring, as well as a combination of mirroring and rotation are just as possible as the generation of mixed panels, i.e. a panel with different circuits (Fig. 1). The software also handles the numbering of the individual boards.
In order to ensure traceability, it is important that the numbering of the individual circuits on the panel is the same for all process steps of the PCB production. In addition, it is possible to merge the panel via a merge function into an entire PCB board.
Simple and secure test fixture design
The more boards to be tested there are on one panel, the more complex the design of the respective test fixture. Until now, even that was manual work or it was left up to the fixture-house, but by this the user lost influence, e.g. on the allocation of channel numbers (i.e. the numbering of the test pins). Test fixtures cost a lot of money, so their conception and manufacturing must be fault free. C-LINK significantly facilitates reliable planning of a test fixture (Fig. 2). This can be created fully automatically or partially manually, as desired.
In addition, for example, if a pin of the test fixture is manually placed on a PCB, then the position can be transferred to all boards of the panel. The label positions for the pins or the pin properties themselves can also be created only once on a circuit instance and then transferred to all other PCBs. That way no redundancies arise that could lead to annoying faults with subsequent changes. The allocation of the channel numbers is also flexible and “readably” possible with the software with optimal utilization of the available tester hardware. Finally, fixture documentation with all the individual channel numbers of the entire panel is generated. In the end, this facilitates the test documentation and traceability. Fixtures with the possibility to test also individual circuits, for example field returns, are also easy to plan (Fig. 3).
Simple and flexible test definition
Elaborate test program debugging is also often a challenge in a panel test. This is supported by the Digitaltest Computer Integrated Test Environment (CITE). Here, all test parameters are created only once and then automatically transferred to all PCBs of the panel (Fig. 4). However, what is important here is the openness and flexibility for exceptions and irregularities, for example if a more expensive test resource is to be used successively by all boards, e.g. a power supply. It can also be flexibly selected whether tests for the entire panel or for each individual board should be documented separately.
For this purpose, a bar code on the panel is scanned and assigned a unique identifier (depending on the specifications of the respective application) via the position of each board on the panel. The entire concept also works with mixed panels. In addition to the test software, the user interface of the test program in CITE can be easily adapted to individual needs. For traceability, the software also stores all test data in a database. The software can be used to significantly reduce the overhead of creating panel tests compared to a single test.
Parallelization eliminates panel test bottleneck
However, not only the planning of tests and test equipment is challenging, but the practical implementation of the tests is as well. If all boards on the panel are sequentially tested in a conventional manner, this can slow down the entire production line. When using a test system with several test heads (Lambda edition), two or more boards can be tested simultaneously in parallel. This reduces the cycle time and the throughput on the tester increases accordingly. One PC can control several test heads, which are connected to the panel via an adjusted adaptation (Fig. 5).
The Lambda edition software provides all the functions needed to control such a parallel test. This includes both the communication with the operator or handling system as well as the control and possibly synchronization of the test processes. Maximum performance is achieved when all test steps are executed in parallel. In addition, the Lambda edition is designed to be very flexible, for example, one expensive hardware resource can only be installed once and the software coordinates or synchronizes the respective use sequentially. This can cost-effectively achieve optimum throughput. The software of the Lambda edition is divided into the actual test programs and a coordinator, which controls the parallel running tests. Thus, with one PC and two test heads, the cycle time of the test station can be halved or reduced with a four-head system to one quarter of the sequential test time.
Very complex or computationally intensive test processes can be sped up by using a second PC. The test programs are automatically transferred from the coordinator PC to the other computers and thus kept up-to-date. The coordinator and test program are based on a modular system that can be flexibly adapted to individual requirements.
Finding and resolving faults
If faults are discovered during the panel test, it is important that they can be assigned to the correct individual PCBs. Here, the failure import module of the QMAN repair software uses intelligent procedures to clearly assign failures to the respective board. This ensures that faults detected in the panel test can be quickly found on the individual circuit and can therefore be repaired at low cost.
It becomes clear: The test professionals have seen the challenges in the market and developed consistent solutions for them. It was important to them that they could be used with just the push of a button for standard test tasks. At the same time, however, a solution was created that can be flexibly adapted to individual needs. Whether for simple or complex test applications, the system supports the user perfectly throughout the entire process from panel creation, through test debugging, to tests and final documentation.
As a leading partner in the electronics industry, Digitaltest GmbH (Stutensee, Germany) has been developing and producing automated test systems (ATE) for electronic circuit boards, software for automating production, and quality management systems for nearly 40 years. Digitaltest is known for innovative solutions for optimizing the entire manufacturing process – as an interface between CAD, the testing process, and production itself. We also offer comprehensive service and support, including complete outsourcing of PCB testing at Digitaltest locations around the world. Digitaltest’s software and hardware products are used in many key industries, including aerospace, automotive, telecommunications, medical, and industrial and consumer electronics. With more than 2,500 installations worldwide, the company is a proven industry partner. Contact: firstname.lastname@example.org
About the authors:
Martin Bader is Director Sales/Customer support at Digitaltest.
Jürgen Holzinger is CITE Product Manager at Digitaltest.
Olaf Rohrbacher is C-LINK/QMAN Product Manager at Digitaltest.
All images © Digitaltest GmbH