As an electronic circuit designer, one of the greatest thrills is finally nailing down a design that meets client objectives and performance demands. Sometimes, the design process begins with a vague description of the expected end result and the designer is responsible for filling in the blanks regarding specific components, component layout, the number of layers, the size of traces and even the type of board. Finding a solution that adheres to client demands and technical requirements seems daunting at times but constitutes what being a designer is all about: finding answers. But regardless of the specific variables involved in a given project, the factor that remains constant is that the designer’s job is not complete until PCB testing has been completed.
Although applying circuit board testing methods to your PCB is a constant requirement for all designs, the specific testing methods used by your contract manufacturer (CM) may vary a great deal. The types of tests conducted your board during manufacturing are among the quality control (QC) options that differentiate CMs. Some CMs perform virtually no testing as part of their standard manufacturing services, while others provide extensive board compliance verification. If your PCBs are utilized in governmental, medical or space systems, then high-end testing, including adherence to standards such as IPC 2 or 3, is probably required. Even if your PCBs are not intended for the most sensitive applications, you still need to be confident in the quality of your boards. Therefore, you should be aware of the circuit board testing methods employed by your CM, as they are an important aspect of the PCB manufacturing process and directly impact the time and cost of your PCB development.
Circuit Board Testing Methods for Manufacturing
The application of circuit board testing during PCB manufacturing not only provides a pillar of confidence, but has practical implications as well. Verifying your board’s quality allows you to focus strictly on functional testing during prototyping, enabling you to easily transition to production with the assurance that your PCB will perform as desired in the field. The application of your PCB has a significant impact on the circuit board testing methods that your CM should use. However, this should not be the sole consideration of your QC regimen because board type also plays a significant role. Let’s examine circuit board testing methods that your CM may employ for rigid PCBs and explore specialized methods you may consider if your design calls for flex or rigid-flex boards.
Circuit Board Testing Methods for Rigid PCBs
The most common method to check PCB construction quality is visual inspection, which is typically performed throughout the PCB manufacturing process. This type of inspection is critical as it supports some automatic fabrication and assembly steps. However, detailed testing and sophisticated equipment are required to provide high-level QA. Below is a list of QA tests and the information they yield about your board:
- Peel Test - used to determine the amount of strength required to peel laminate from board.
- Solder Pot Test - determines the solderability of plated through hole (PTHs).
- Solder Float Test - measures the degree of thermal stress that a PCB hole can withstand.
- X-ray Inspection – used to view the PCB’s internal construction; including layers and vias. Can also be used to view inside of component packages to verify device types and authenticity.
- Automated Optical Inspection AOI – performed to check solder quality and verify pad and trace connections.
- Time Domain Reflectometry (TDR) – typically done to measure characteristic impedances. Can determine if differential traces are matched for good signal integrity.
- Resistivity of Solvent Extract (ROSE) Testing – highly reliable test used to ensure that your board does not contain significant surface debris remaining from manufacturing processes or excess conductive material.
Circuit Board Testing Methods for Flex and Rigid-Flex PCBs
Full or partly flexible PCBs present special issues for manufacturing, as boards have to meet the same quality requirements as rigids boards, while being bendable. To guide CMs in producing flex boards, IPC has published a number of guidelines and standards, the most important of which is IPC-6013C, Qualification and Performance Specification for Flexible Printed Boards. IPC-6013C defines materials, performance requirements and tests that should be performed to ensure the quality of flex PCBs. These tests include QA tests performed on rigid boards, as well as a bend test.
The bend test should be based on whether the board will be installed in a flex position, to flex dynamically or to only bend once. The specific usage category the board falls into determines the degree or bend radius the board must be able to attain.
Bend Test Requirements for Flex and Rigid-Flex PCBs
Circuit Board Testing Methods Summary
Regardless of whether your PCB design involves a rigid, flex or rigid-flex board, you need to ensure your CM performs adequate testing to ensure top quality. The circuit board testing methods that your CM typically employs will primarily depend on your board application; it is up to you to ensure that the testing performed meets your desired requirements. To assist you in determining what tests to request, the following table summarizes some common testing methods and the information the results will give you regarding your board quality.
As shown, the QA tests above provide definitive results, such that the quality of your PCBs can be easily determined and if design or manufacturing changes are required. Industry manufacturers institute additional tests as well; however, the above table provides common testing methods that cover the most important board attributes to ascertain your board’s quality. Once your PCB has successfully met the requirements for the circuit board testing methods employed by your CM, then your design is complete in terms of QA testing.
The PCB Design Development Checklist
At Tempo Automation, we specialize in developing high-quality PCBs and serve the military, aerospace, medical and automotive industries, which have the topmost standards for quality. Our fast turnkey PCB manufacturing process is built upon advanced technology and software-driven automated processes that include X-ray inspection and AOI as part of our standard circuit board testing.
We will collaborate with you to optimize your design from day 1 and provide transparent DFM specifications along with access to DRC files, which can be downloaded and incorporated into your software if you’re an Altium user.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on circuit board testing methods and how to prepare your PCB to be tested during manufacturing, contact us.
|Tempo‘s Custom PCB Manufacturing Service