PCB Bare Board Test
In order to enable manufacturers to reduce production costs while fully guaranteeing the electrical performance of bare board interconnection, users will need to ensure 100% network data compatibility. This is currently one of the challenges faced in the industry. Industry professionals are anticipating the development of industry standards in the near future to address these issues. Historically, the processes in this area have not been perfect. For instance, the industry previously provided circuit board manufacturers with Gerber machine code, which was used to drive the light plotter and generate the mask tool that defines the light pattern of the production circuit board, whether it be single-sided, double-sided, or multi-sided lightmap. However, existing software tools were only able to extract netlist information from Gerber graphs, which did not include component information – it only defined the conductive connections that existed due to machine code commands. The early industry standard for data formats was IPC-D-356.
This data format extracted netlist information from the CAD system and replaced it with intelligent machine code. Many testers utilized this code to determine the netlist characteristics corresponding to the physical condition of the circuit board. Since the bare board testing is carried out after the wiring process is completed, the IPC-D-356 format provides information related to the pin information of a single component. Thus, manufacturers who test according to the IPC-D-356 standard can provide information such as “the 16 pins of the U14 component are shorted to the 9 pins of the U20”.
CAD netlist data is the most essential electronic data for bare board testing. Although many companies are hesitant to share this information with circuit board manufacturers, it remains the most concise data for determining whether the bare board performance aligns with the CAD system design requirements. It is expected that the electronic description of the three formats of the circuit board should be consistent with each other, but in most cases, this is not the situation. There are three reasons for this discrepancy in description: hasty changes, data conversion challenges between machine code data and netlist data, and issues in software implementation. Nonetheless, data compatibility is crucial.
Open circuit and short circuit tests using fixtures and needle beds are also facing challenges as circuit boards become more complex, making them unable to meet circuit test requirements due to reduced circuit size and increased component density. Most circuit board manufacturers use single-density, double-density, and four-density test beds. The double-density test bed is suitable for spacing of 400 mm and above, with other technologies needing to be considered when the board density exceeds 400 mm pitch. This type of test mainly encounters more array-shaped packages, such as BGA or column grid arrays, or fine-pitch BGA packages with closer pins.
The focus of this section is on bare board testing, but to ensure the correct installation of various parts during assembly, the circuit board manufacturer must ensure that the signal inlet and outlet of each wiring network on each array pad are connected correctly to the signal inlet and outlet of other related wiring networks while also eliminating short-circuit faults. The four-density test fixture can have 62 test pins per square centimeter, though there are concerns regarding potential damage to the circuit board from probe contact. Additionally, the cost of dual-density and four-density fixtures, as well as the overall test instrument, is relatively high, making it challenging to stay within the expected cost range. The cost is expected based on the current understanding of electrical performance testing and linear expectations of existing test concepts. Some circuit board manufacturers use flying probe test as an alternative, where each wiring network can be stimulated and compared with neighboring wiring networks to identify open-circuit and short-circuit characteristics.
Flying probe testing eliminates the need for a fixture and its cost depends on the number of circuit boards produced. It is a low-cost and effective alternative to bed of needle testing, although it has a relatively slower speed and a higher equipment price. Testing becomes more complicated when dealing with high-density circuits and other wiring networks.
In order to enable manufacturers to reduce production costs while fully guaranteeing the electrical performance of bare board interconnection, users will need to ensure 100% network data compatibility. This is currently one of the challenges faced in the industry. Industry professionals are anticipating the development of industry standards in the near future to address these issues. Historically, the processes in this area have not been perfect. For instance, the industry previously provided circuit board manufacturers with Gerber machine code, which was used to drive the light plotter and generate the mask tool that defines the light pattern of the production circuit board, whether it be single-sided, double-sided, or multi-sided lightmap. However, existing software tools were only able to extract netlist information from Gerber graphs, which did not include component information – it only defined the conductive connections that existed due to machine code commands. The early industry standard for data formats was IPC-D-356.
This data format extracted netlist information from the CAD system and replaced it with intelligent machine code. Many testers utilized this code to determine the netlist characteristics corresponding to the physical condition of the circuit board. Since the bare board testing is carried out after the wiring process is completed, the IPC-D-356 format provides information related to the pin information of a single component. Thus, manufacturers who test according to the IPC-D-356 standard can provide information such as “the 16 pins of the U14 component are shorted to the 9 pins of the U20”.
CAD netlist data is the most essential electronic data for bare board testing. Although many companies are hesitant to share this information with circuit board manufacturers, it remains the most concise data for determining whether the bare board performance aligns with the CAD system design requirements. It is expected that the electronic description of the three formats of the circuit board should be consistent with each other, but in most cases, this is not the situation. There are three reasons for this discrepancy in description: hasty changes, data conversion challenges between machine code data and netlist data, and issues in software implementation. Nonetheless, data compatibility is crucial.
Open circuit and short circuit tests using fixtures and needle beds are also facing challenges as circuit boards become more complex, making them unable to meet circuit test requirements due to reduced circuit size and increased component density. Most circuit board manufacturers use single-density, double-density, and four-density test beds. The double-density test bed is suitable for spacing of 400 mm and above, with other technologies needing to be considered when the board density exceeds 400 mm pitch. This type of test mainly encounters more array-shaped packages, such as BGA or column grid arrays, or fine-pitch BGA packages with closer pins.
The focus of this section is on bare board testing, but to ensure the correct installation of various parts during assembly, the circuit board manufacturer must ensure that the signal inlet and outlet of each wiring network on each array pad are connected correctly to the signal inlet and outlet of other related wiring networks while also eliminating short-circuit faults. The four-density test fixture can have 62 test pins per square centimeter, though there are concerns regarding potential damage to the circuit board from probe contact. Additionally, the cost of dual-density and four-density fixtures, as well as the overall test instrument, is relatively high, making it challenging to stay within the expected cost range. The cost is expected based on the current understanding of electrical performance testing and linear expectations of existing test concepts. Some circuit board manufacturers use flying probe test as an alternative, where each wiring network can be stimulated and compared with neighboring wiring networks to identify open-circuit and short-circuit characteristics.
Flying probe testing eliminates the need for a fixture and its cost depends on the number of circuit boards produced. It is a low-cost and effective alternative to bed of needle testing, although it has a relatively slower speed and a higher equipment price. Testing becomes more complicated when dealing with high-density circuits and other wiring networks.
