Electrical Test
In the production process of PCB boards, it is inevitable that electrical defects such as short circuits, open circuits, and leakage will be caused by external factors. Additionally, PCB boards are continuously evolving towards high density, fine pitch, and multi-level designs. Allowing defective boards to flow into the production process will result in increased cost wastage. Hence, alongside process control improvements, enhancing testing technologies can lead to reduced scrap rates and improved product yields for PCB manufacturers.
In the manufacturing of electronic products, the cost incurred due to defects varies at each stage of production. The earlier a defect is detected, the lower the cost of rectification. “The Rule of 10’s” is commonly used to evaluate the costs associated with addressing defects in PCB boards at different stages of production. For instance, if an open circuit is identified in a bare board in real-time, it generally only requires a line repair or at most, the loss of one bare board. However, if the open circuit goes undetected and the board progresses to downstream assembly where parts are added, furnace tin and IR remelting take place, resulting in additional costs for parts replacement and rework.
In a worst-case scenario, if a defective board remains undetected through assembly testing and is incorporated into a final product such as a computer, mobile phone, or automotive component, the cost of rectifying the defect at this stage is significantly higher than if it had been caught earlier. Thus, for the PCB board industry, electrical testing plays a crucial role in identifying boards with functional circuit defects promptly.
Downstream manufacturers often require PCB board manufacturers to perform 100% electrical testing to ensure quality. Prior to testing, both parties must agree on test conditions and methods. To do this, they must define the following:
1) Test data and format
2) Test conditions such as voltage, current, insulation, and continuity
3) Equipment production method and selection point
4) Testing procedures
5) Patch specifications
During the manufacturing process of PCB boards, testing is necessary at three key stages:
1) After etching the inner layer
2) After etching the outer layer circuit
3) Upon completion of the finished product
In each stage, there are typically 2-3 100% tests conducted to identify defective boards. These boards are then reworked. The test station serves as a data collection point for analyzing process issues. Statistical results help identify problems such as open circuits, short circuits, and insulation issues. After rework, further testing is done. By analyzing the data, quality control methods can pinpoint the root cause of any problems for resolution.
2. Methods and Equipment for Electrical Measurement
Various electrical testing methods exist, including Dedicated, Universal Grid, Flying Probe, Non-contact Electron Beam (E-Beam), Conductive Cloth (Glue), and Capacity and Brush Test (ATG-SCAN MAN). The most commonly used equipment includes special test machines, general test machines, and flying probe test machines. To better understand the capabilities of these devices, let’s compare the features of each:
1. Dedicated Test: This test is specific to a particular part number and cannot test different boards. It can test up to 10,240 points for single-sided boards and 8,192 points for double-sided boards with a limited test density.
2. Universal Grid Test: This test is designed based on the grid layout of the PCB circuit. It allows for testing multiple part numbers and offers a high number of test points. The test density can reach QFP.
3. Flying Probe Test: This test involves moving two probes x, y, and z to test each line endpoint. It does not require a costly fixture but has a slower measurement speed. It is suitable for high-density boards like MCM.
3. Technical Comparison
Flying probe tests typically yield between 1-20. The test area varies greatly depending on the density and spacing of the boards, with high-density boards requiring slower testing speeds. Flying probe testers can cover 3,000 to 5,000 square meters per year. While Bed-of-Nails test equipment is less commonly used for high-density boards, it can offer higher output in theory. In practice, special-purpose test equipment is used more in mass production, while general-purpose types are favored for smaller productions. Overall, the cost of testing makes up only about 2-4% of the total price, making general-purpose and special-purpose models popular choices for mass production. As electronic product designs evolve rapidly, the choice of testing equipment must adapt to shorten product life cycles.
In the production process of PCB boards, it is inevitable that electrical defects such as short circuits, open circuits, and leakage will be caused by external factors. Additionally, PCB boards are continuously evolving towards high density, fine pitch, and multi-level designs. Allowing defective boards to flow into the production process will result in increased cost wastage. Hence, alongside process control improvements, enhancing testing technologies can lead to reduced scrap rates and improved product yields for PCB manufacturers.
In the manufacturing of electronic products, the cost incurred due to defects varies at each stage of production. The earlier a defect is detected, the lower the cost of rectification. “The Rule of 10’s” is commonly used to evaluate the costs associated with addressing defects in PCB boards at different stages of production. For instance, if an open circuit is identified in a bare board in real-time, it generally only requires a line repair or at most, the loss of one bare board. However, if the open circuit goes undetected and the board progresses to downstream assembly where parts are added, furnace tin and IR remelting take place, resulting in additional costs for parts replacement and rework.
In a worst-case scenario, if a defective board remains undetected through assembly testing and is incorporated into a final product such as a computer, mobile phone, or automotive component, the cost of rectifying the defect at this stage is significantly higher than if it had been caught earlier. Thus, for the PCB board industry, electrical testing plays a crucial role in identifying boards with functional circuit defects promptly.
Downstream manufacturers often require PCB board manufacturers to perform 100% electrical testing to ensure quality. Prior to testing, both parties must agree on test conditions and methods. To do this, they must define the following:
1) Test data and format
2) Test conditions such as voltage, current, insulation, and continuity
3) Equipment production method and selection point
4) Testing procedures
5) Patch specifications
During the manufacturing process of PCB boards, testing is necessary at three key stages:
1) After etching the inner layer
2) After etching the outer layer circuit
3) Upon completion of the finished product
In each stage, there are typically 2-3 100% tests conducted to identify defective boards. These boards are then reworked. The test station serves as a data collection point for analyzing process issues. Statistical results help identify problems such as open circuits, short circuits, and insulation issues. After rework, further testing is done. By analyzing the data, quality control methods can pinpoint the root cause of any problems for resolution.
2. Methods and Equipment for Electrical Measurement
Various electrical testing methods exist, including Dedicated, Universal Grid, Flying Probe, Non-contact Electron Beam (E-Beam), Conductive Cloth (Glue), and Capacity and Brush Test (ATG-SCAN MAN). The most commonly used equipment includes special test machines, general test machines, and flying probe test machines. To better understand the capabilities of these devices, let’s compare the features of each:
1. Dedicated Test: This test is specific to a particular part number and cannot test different boards. It can test up to 10,240 points for single-sided boards and 8,192 points for double-sided boards with a limited test density.
2. Universal Grid Test: This test is designed based on the grid layout of the PCB circuit. It allows for testing multiple part numbers and offers a high number of test points. The test density can reach QFP.
3. Flying Probe Test: This test involves moving two probes x, y, and z to test each line endpoint. It does not require a costly fixture but has a slower measurement speed. It is suitable for high-density boards like MCM.
3. Technical Comparison
Flying probe tests typically yield between 1-20. The test area varies greatly depending on the density and spacing of the boards, with high-density boards requiring slower testing speeds. Flying probe testers can cover 3,000 to 5,000 square meters per year. While Bed-of-Nails test equipment is less commonly used for high-density boards, it can offer higher output in theory. In practice, special-purpose test equipment is used more in mass production, while general-purpose types are favored for smaller productions. Overall, the cost of testing makes up only about 2-4% of the total price, making general-purpose and special-purpose models popular choices for mass production. As electronic product designs evolve rapidly, the choice of testing equipment must adapt to shorten product life cycles.
