PCB Manufacturing

Circuit Card Assembly Testing: Tips and Best Practice

When the printed circuit board assembly is done, the testing is the essential step to determine whether the final PCB can be put into use. So mastering circuit card assembly needs to be in hand for every PCB manufacturer.

What is Circuit Card Assembly Testing?

Testing of circuit card assembly (CCA), otherwise known as printed circuit board assembly (PCBA), is an integral part of quality control in manufacturing. With the heightened complexity of circuit cards, increasing density and number of components, the electronic tests must improve on effectiveness as well. Defects are potentially induced during assembly and need to be screened out through testing to prevent getting shipped to customers. Circuit card assembly testing is an effective quality verification step in circuit card assembly which we will further expound on in the following sections.

Benefits of Circuit Card Assembly Testing

Even with advanced assembly machines and intelligent Automated Optical Inspection (AOI), circuit card assembly testing cannot be skipped as circuit card assembly testing is a very vital process in verifying the quality of the boards. Below is the comprehensive list of benefits of circuit card assembly testing:

  • Cost Impact of Circuit Card Assembly Testing

Circuit card assembly testing equipment requires huge capital investment due to sophisticated tooling, built-in software, and automation. Despite this, circuit card assembly testing is still a prerequisite before shipment due to the cost itself. With circuit card assembly testing, boards are ensured to be working as intended preventing expensive costs, repairs, and customer dissatisfaction. Early feedback on assembly issues immediately stops the problem from affecting larger volumes that could lead to significant resource wastage.

  • Quality Control of Circuit Card Assembly Testing

Process variation cannot be 100% avoided. Circuit card assembly testing is a method to detect upfront assembly issues brought about by process variations. As earlier mentioned, visual inspections cannot guarantee a ‘good’ printed circuit board. Circuit card assembly testing ensures that the PCBs to be shipped will be able to electrically function as designed. Circuit card assembly testing is also important to ensure that the test program will be able to capture the defects. There are unwanted cases wherein rejects escape testing due to loopholes in the development of test programs and procedures. Rigorous test validation is required before deployment to mass production. Lack of test verification due to urgency to release in mass production may entail design flaws and gross failures.

  • Tool for Continuous Improvement

With circuit card assembly testing, device performance is more understood. The detected electrical faults can be analyzed for potential causes and improved by means of implementing preventive actions. Immediately, failed PCBs can go through failure analysis to spot the defect, determine the affected component and report to the assembly team or design engineers for solutions.

Types of Circuit Card Assembly Testing

There are two types of circuit card assembly testing which have different advantages and disadvantages: Flying Probe Testing and In-Circuit Testing (ICT). For both types, electrical signals are applied using test pins and determining the corresponding output signals.

  • Flying Probe Testing

Flying Probe Testing in Circuit Card Assembly Testing

Flying Probe Testing is a type of circuit card assembly testing that uses probes that can quickly move to test the different contact points of the circuit card. In this method, a fixture is not required but the test time is longer due to the limited number of moveable probes. Flying probe testing is generally used for small-scale and low-volume production but there are also efforts to optimize and speed up flying probe testing by increasing the number of probes, reducing the number of required tests and minimizing the movement of the probes.

  • In-circuit Testing

In-circuit Testing in Circuit Card Assembly Testing

In-circuit Testing is another type of circuit card assembly testing which consists of a fixture with probes to contact circuit nodes and track electrical performance. The probe count is equivalent to the number of test points in the PCB. In-circuit testing has fast testing and diagnostic time. ICT provides prompt detection of manufacturing faults like wrong components, wrong orientation of chips, and open and short circuits. The programming sequence can easily be derived from the Gerber files of the circuit card tool. Some drawback of using ICT is the high cost of the needed probe tooling and automated mechanism. Design modifications for ICT are also more difficult due to the required automation and the entire tooling must be changed which entails cost.

Functional Testing is being done by detecting faults during operating environment simulations. The functional tester inputs a signal and measures the response of the printed circuit board. The functional tester has a fast-go or no-go test capability and a slow diagnostic time. Functional testing often provides general rejection messages which are subject to test engineering interpretation.

Circuit Card Tester Set-up

Below are the minimum relevant check items of the circuit card tester prior to production use:

  • Functionality Check

Functionality check means knowing if the tester will be able to detect the reject and good units correctly. It involves testing master samples (good and reject parts) to know if the tester will provide correct readings.

  • Pogo Pin Life Cycles

Pogo pins are consumable parts that have defined tool life. Due to frequent touchpoints with the circuit card contact pads, pogo pin life that is counted based on touchpoints must be tracked every use to determine if it has already exceeded the specified limits. The pogo pins must also be checked for foreign materials or contamination as they may interfere with the testing of the parts.

  • Machine Maintenance

The test operator or technician must check if the tester is calibrated and maintained according to the established frequency. The tester should have a PM (Preventive Maintenance) and calibration sticker which contains the date of the last calibration or Maintenance. This information will be used as a reference by the technician or operator if the tester is qualified to be used.

Potential Causes of Circuit Card Assembly Testing Failures

Potential Causes of Circuit Card Assembly Testing Failures

The failures that circuit card assembly testing can come from various sources. Below are the three broad categories by which circuit card test failures can be grouped:

  • Material-related Failures

PCB test failures can also be caused by material-related issues such as component faults, and defective materials. These material issues are the reason why it is essential to put incoming quality controls before circuit card assembly and on top of the material outgoing inspection of the vendor.

  • Board Design Failures

The second category of potential cause of test failures is board design issues. Common design-related issues include excessive noise, signal distortion and component incompatibility.  This is why efforts must be exhausted during prototyping to ensure that the design is working properly.

  • Process Variation

Some defects can occur during assembly and lead to electrical failures. A very low first-pass yield of less than 85% may be indicative of assembly problems. Test failures like shorting can be caused by process defects such as solder bridging, contamination by conductive materials, and component misalignment while open circuits can be a result of lack of solder, broken traces, or misaligned components. The potential causes of these defect types greatly vary from machine set-up.

Some circuit cards can have marginal electrical results at the boundaries of test specifications, which may be caused by physical or chemical changes in the components through heat and mechanical stresses. A dangerous thing that could happen is latent failures that neither Automated Optical Inspection (AOI), X-ray inspection nor circuit card assembly testing could detect. These are usually caused by cracks or unnoticeable delamination that could have passed electrical testing but get aggravated during field applications.

Additional Resources:

    Request for Quote

    Related Posts