One of the greatest causes of anxiety is being tested. Regardless of whether it is an academic exam, medical evaluation, or a job interview, having to undergo an assessment can cause even normally steady individuals to become nervous and apprehensive. Nevertheless, testing, if done objectively, can provide very useful information about a student’s understanding of the course material, a patient’s health, or a candidate’s match for a position.
Testing is also a very useful and important tool for evaluating whether a PCB will be able to meet its performance and reliability objectives. Performance testing, in fact, is one of the three major stages of the PCB prototype iteration cycle that define the quality of your board’s development. Once the desired quality level is reached, it is recommended to evaluate the board’s ability to maintain its form factor for its intended application and over the operational lifecycle. Let’s define PCB structure types and then discuss how a circuit board can be tested for structural integrity.
Types of Circuit Board Structures
The construction of a PCB is a well-defined process divided into two stages: fabrication and assembly. During fabrication, the physical architecture of the board is realized, which includes the stackup of layers, drilling of holes, etching of copper traces, and application of solder masking. The assembly stage is where your component selections are attached to the board and most inspections are performed. This process consists of essentially the same steps for all circuit board structures. However, boards can vary widely in form factor.
Circuit Board Structures
Although circuit boards may be designed for almost endless sizes and shapes, all of them can be classified as rigid, flex, or rigid-flex PCB structures.
Rigid PCBs are by far the most utilized in electronics devices and systems. These boards are meant to retain their shape or form factor through the operational lifecycle and within whatever environment they are deployed.
Flex boards have distinct advantages over rigid boards. Primarily, they are bendable which allows for installation or mounting in areas where rigid boards can be placed.These include lighter weight material fabrication, the ability to withstand vibration and mechanical shocks, three-dimensional packaging geometries, and superior heat dissipation capability. However, flex boards are typically more expensive than rigid PCBs.
Rigid-flex boards seek to leverage the bendability of flex PCBs while also leveraging the advantages of a rigid structure. Combining these attributes in a single board provides design flexibility. For example, it is common for boards to be rigid for planar component placement and flexible for trace routing.
All circuit boards are categorized under IPC-6011, Generic Performance Specification for Printed Boards, as either class I, class II, or class III based upon their performance expectations and end use. Additionally, circuit board flexibility is defined by type under IPC-6013D Qualification and Performance Specification for Flexible/Rigid-Flexible Printed Boards. As stipulated in the standard, these are:
- Type 1 – Single-sided flexible printed boards containing one conductive layer, with or without stiffeners.
- Type 2 – Double-sided flexible printed boards containing two conductive layers with PTHs, with or without stiffeners.
- Type 3 – Multilayer flexible printed boards containing three or more conductive layers with PTHs, with or without stiffeners.
- Type 4 – Multilayer rigid and flexible material combinations containing three or more conductive layers with printed through holes (PTHs).
- Type 5 – Flexible or rigid-flex printed boards containing two or more conductive layers without PTHs.
Now, let’s take a look at structural testing for rigid, flex or rigid-flex boards.
How to Test a Circuit Board for Structural Integrity
Reliability demands that your board is able to operate as intended within the environment that it is employed, consistent with its performance classification requirements. Therefore, you need to institute a testing regimen to verify your PCB’s ability to maintain its form factor without cracking, permanent deformation or breaking prior to delivery to your client(s). This regimen should be based on the requirements and suggestions put forth in IPC-6013D.
For all boards, there are additional circuit board tests that can be performed to verify your board’s structural integrity. These include manual and automatic inspections, such as X-ray and automated optical inspection (AOI) that provide a view of the board’s structure, and invasive tests, such as the peel test that defines the force required to separate the laminate from a substrate and the solder float test where the ability of a drill hole to withstand thermal stress is measured. Following the procedure below should result in an effective structural testing regimen for your rigid, flex or rigid-flex board.
- Determine your board’s general classification using IPC-6011.
- Determine your board type using IPC-6013D.
- Follow the testing requirements given in IPC-6013D.
- If possible, duplicate your board’s deployment environment and test board.
- If the yield rate is unacceptable, then review the design for the target area of failure. For this review, it is advisable to utilize IPC-2223 Sectional Design Standard for Flexible/Rigid-Flexible Printed Boards to ensure that your design specifications and decisions adhere to the standard.
- For flex type boards, ensure that the bend test requirements for installation, as shown below.
Bend Test Requirements for Flex and Rigid-Flex PCBs
In order for your boards to meet the quality and reliability expectations for their application, the PCBs must be able to withstand the structural challenges to which they will be confronted. To ensure this, effective testing must be done prior to deployment.
|Tempo‘s Custom PCB Manufacturing Service|
Many of the testing methods that will provide the best feedback on your boards' structural integrity can be performed by your contract manufacturer (CM). At Tempo Automation, the industry leader in fast, high-quality PCB manufacturing, we utilize standard manual and automatic inspections to assess your boards during manufacturing. Additionally, we are capable of performing additional ICT testing to verify the quality of your boards.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.
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 how to test a circuit board or the structural integrity of PCBs, contact us.