In today’s aspect of the electronics manufacturing industry, especially in the production of printed circuit boards or PCBs, it is vital to always guarantee that the boards are good before proceeding for assembly. One of the basic activities in this regard is the Bare Board Test, namely the PCB open short test.
Let’s understand the basic meaning of the Bare board test in simple words. This first inspection or checking of the PCB is carried out before the addition of different electronic components, and its purpose is to check for any flaws that may affect the efficiency, capability, and durability of the device. In this article, we have highlighted a detailed process of how to conduct the Bare Board Test and what are the vital different methodologies and crucial steps that need to be considered while performing an excellent inspection.
Importance of Bare Board Test
1. Early Detection of Defects
The facilitation of open circuits, shorts and wrong trace routing are better detected at an early stage of the manufacturing cycle hence it would cut down costs of corrections. In this way, flawed boards do not reach the assembly stage where the cost and difficulties of repairs are much higher.
2. Ensuring Design Integrity
This test confirms that the manufacturing of the boards corresponds to the design files created during the designing of the circuits by the PCB designer. It guarantees that the PCB will work as it was designed within the final tailored product or device.
3. Compliance with Standards
Policies and procedures aimed at the improvement of existing processes must also meet The requirements of the industry and the customers should be followed. Thus, this process helps in confirming that boards, that are developed meet these specifications and are reliable to perform in the field.
4. Cost Savings
It is easier, cheaper and more efficient to identify and handle the bare boards with defects rather than gripping with the assembled boards. This has a net effect of increasing profitability since production costs are decreased.
A Bare Board Test is a relatively simple process and the following words will provide you with a step-by-step guide to complete such a bare board test.
Preparing for the Bare Board Test
Before conducting the Bare Board Test, several preparatory steps are necessary which are as follows:
1. Review Design Files
Collect each Gerber file or other design documentation to assess such areas in the PCB layout as it gives information about defined trace routing and connectivity. This aids in the determination of test parameters and hence helps in the conduction of the right framework.
2. Set Up Test Equipment
An important aspect is the preparation of test equipment. Normally, a Flying Probe Tester or Bed of Nails Tester is used. for this process. Make sure that the equipment is set right and works according to the industry standards
3. Inspect the Bare Boards
Before protecting the bare boards, perform a preliminary inspection to look for any signs of manufacturing flaws or other irregularities, including inconsistencies in the layers’ alignment, signs of short circuits, or other deformities on the bare board.
Conducting the Electrical Bare Board Test
In the Bare Board Test, the main function is to electrically test the PCB to check whether the printed circuit board is good or bad. This process is conducted by performing a fly probe test. let’s learn about this bare board test.
Flying Probe Test
It is performed by using an instrument known as a fly probe tester. The Flying Probe Tester works in a way that has two or three probes that are located on an axis-mapped table. They will connect to the required test points on the PCB. The method is suitable for small to medium scale production and in the bare board test of prototypes because of its versatility and short cycle time.
Starting from the first test point, the tester proceeds by placing the probes successively to the next test points, and the absence of continuity means that there is a short or open. That is why it is called PCB open short test. The procedure is fully automated and managed by the software.
The results obtained are then checked with the initial design values.
Once the electrical tests are completed, the results must be analyzed to identify any defects or issues. let’s learn about a few testing parameters
- Continuity Testing: – it ensures pins out connectivity signs to all the traces, vias and the pads. Any orange and red colouration means that there are broken or missing traces and we will be able to observe them on the PCB.
- Isolation Testing: -It ensures that there is no development of short circuits of the traces. There may be safety problems that indicate why shorts are there. Hence, understanding and finding ways of addressing these problems is worthwhile.
- Impedance Testing: -Impedance test when done frequently helps in establishing that the fabricated PCB traces have the right impedance value. This is important to minimize signal interaction, particularly in designs that have very high-speed transitions.
All the results are recorded and the presence of any defects and their position is noted. All the information that is used in the course of diagnostic and analytical activity is useful for manufacturers.
Addressing Defects and Re-Testing
Identifying defects is only the first step, addressing them effectively is crucial for ensuring the quality of the final product
Knowing the defects means that a correct approach to them should be taken for the desired quality of the final product. Here are 2 processes involved in addressing and repairing the defects in the whole bare board test.
- Repairing Defects: Concerning the type of defect, the repair is wetting and re-working of the traces, It is necessary to have skilled technicians to conduct these repairs to avoid giving devices inconsistent results.
- Re-Testing: After repairing, the PCB has to be tested again to ensure all the problems are well solved. This helps one to be very confident that the repaired boards are as good as healthy boards with regard to all the design criteria and specifications. This step is crucial in the PCB open short test.
Final Inspection and Quality Control After PCB Test
The final step in the Bare Board Test process involves comprehensive quality assurance and inspection to ensure that the boards are ready for assembly. The last method for selecting the Bare Board Test is the quality assurance and inspection of the boards to verify that ensures that the boards are in a good state for assembly. The final step plays a vital role in the whole bare PCB testing.
1. Visual Inspection
proper eye inspection establishes that there are no more remaining defects or any form of abnormalities in that region. This includes ensuring that the film and any other layers used in the process undergo comprehensive checks that enable the determination of the visibility.
2. Automated Optical Inspection (AOI)
AOI systems should be used in the second scan to help search for defects on the surface of the PCBs. AOI is helpful when we want to portray other defects which cannot be easily pointed out and such can be fine cracks or other misaligned features.
3. Final Documentation
After all of the above-mentioned processes, we create the final test report that includes the results which were received, the performed repair actions, and the overall quality of the boards. This report can be employed for improvement and development and it is beneficial as a reference of variety quality assurance.
Important Tips Regarding Bare Board Test
Although most of the process of the bare board test has been completed we would like to address some important tips regarding the bare board test.
- Regular Calibration of Test Equipment should be done before every testing process. Ensures that all the test equipment used is in good working condition by being well-calibrated to give the right results.
- Make sure that the technicians and operators comprehend the test procedures, equipment, and methods used to trace the defects.
- Try to Opt for automated testing systems where possible because it makes testing independently precise, fast and accurate.
- Incorporate with the PCB designers to get a far better proofing of design files and as well as to comprehend any change carried out by designers.
- Record the test results as well as the visible defects together with the actual repairs in a fitting manner.
Conclusion
Bare PCB Testing is one of the Preliminary tests that is conducted on PCBs before going for manufacturing of the item. This way, PCB bare board testing ensures that any PCB that may be defective does not get to the assembly of the component stage. As a result, the yields can be high, costs can be cut and clients can be given better outputs during the manufacturing process because of proper planning and bare PCB testing along with the optimization.
