When submitting a PCB design, proper discussions with an electronic contract manufacturer should entail your preferred PCB testing methods. It should become a foundational factor under consideration when approaching an EMS. But it is impossible to have a fruitful discussion without understanding the diverse types of testing methods involved in PCB fabrication and mass production. This section will canvass the primary testing method in depth and their importance in the PCB production process.
In-Circuit Testing
It represents a robust PCB testing approach. In-circuit testing often proves costly, though this also depends on the fixture and board size, among other aspects. The ICT test, alternatively inferred as a bed-of-nails test, actuates and powers the specific circuitry on the circuit board. It often entails 100% coverage by design, though it covers about 85-90% coverage in most instances. However, the coverage, albeit not 100%, often comes devoid of any human error.
In-circuit testing deploys fixed probes that get laid out a particular way and which matches the PCB design. It is the probes that check for the solder connection integrity. The ICT tester pushes the circuit board to the bed containing the probes to initiate the test. Predesigned access points exist on the board, allowing the testing probes to connect with the circuit. Consequently, the pressure applied to the connection ensures it all stays intact.
In-circuit testing often gets performed on BGAs (ball grid arrays) or bigger connections. It applies to “mature” products with very little revisions anticipated. However, a lack of DFM (design-for-manufacturing as an objective in your PCB production may make in-circuit testing impossible to carry out. Unfortunately, it is impossible to switch mid-way into an in-circuit approach.
Benefits
- It has an incredible consistency where you get a similar test every time in a similar fashion.
- ICT also tests every component individually using the automated equipment. Since it checks for the logic functionality aspect, it also powers the components.
- The thorough test coverage reduces the repair and maintenance costs by making other tests pointless.
Flying Probe Test/Fixtureless In-Circuit Test
The PCB flying probe test is a valuable and less expensive testing option compared to in-circuit testing. It is not powered responsible for checking for shorts, opens, capacitance, diode issues, and resistance. It uses needles attached to the PCB probe on the x-y grid from the basic CAD. However, the ECM program must coordinate and matches the circuit board before running the program.
The flying probe test PCB process is essential in printed circuit board assembly for production and prototype volume testing. It arises from the increasing need for innovative PCB features such as increased board access, test speeds, repeatability, and reliability.
Since it uses PCB test probes that fly, it requires no custom fixtures. However, it is important to note that originally, the design permitted the testing of bare boards. It has since evolved into a go-to, all-encompassing test, ideal for PCB assembly.
Benefits
- The flying probe test approach proves more affordable for small-volume production-like testing prototypes.
- FPT fails to pose many accessibility issues compared to in-circuit testers.
- The probe movement gets controlled through a software program and thus proves easy to change and implement
- It requires no built test points as the flying probes have direct access to the component pins via automated probing.
AOI – Automated Optical Inspection
It is a unique testing approach that uses a 2D or 3D camera in taking pictures of the printed circuit board. The images get relayed into a specific program that compares the board images with a comprehensive schematic. Any board that fails to match the reference schematic at a certain cut-off point gets flagged for inspection.
Automated optical inspection becomes useful in detecting issues promptly and preventing any immediate shut down of the production process. However, the testing approach cannot power up the board and may fail to cover 100% of every part type. Additionally, it is advisable to always rely on other testing approaches besides the AOI. Some of the ideal combinations include the following.
- AOI and ICT
- The flying probe and AOI
- AOI, besides functional testing
Benefits
- It identifies faults in real-time and quicker compared to manual inspection.
- AOI gives applicable empirical data for process control and documentation to avoid them in the future
- It uses different strategies to test diverse PCB solder joints, components, etc.
- Data generated can become useful in establishing trends for process enhancements in the future.
Burn-In Testing
It comes with an extra intense testing type for printed circuit boards. By design, it detects any early failures and develops a load capacity. The intensity by which it works can destroy the parts getting tested.
Burn-in testing works by pushing power at its maximum and within the specified capacity through the electronic device. It happens for about 48-168 hours where power gets run through continuous. Whenever a board fails this test, it gets referred to as infant mortality. On this basis, the quota fails to determine the suitability of the PCB’s quality for deployment, especially medical and military applications.
However, burn-in testing is not ideal for every PCB project, as it makes sense for some projects. It can help prevent embarrassing product launches or dangerous products from reaching customers. Burn-in testing has the capability of shortening the lifespan of a product, especially when it subjects your board to undue stress than it can handle. Therefore, you can reduce the test limit to shorter periods to avert overstressing the PCB whenever you cannot identify defects.
Benefits
- It accelerates the lifespan of the component by eliminating premature failures by ridding it off of defective parts.
- It ensures quality for PCBs intended for tough application areas
X-Ray Inspection
Popularly inferred to an AXI, the testing approach proves more of an inspection instrument for many electronic contract manufacturers. It entails a testing method where the X-ray technician identifies defects by looking at solder connections, barrels, and internal traces.
X-ray inspection can come either as a 2D or 3D AXI test. The 3D testing provides a quicker testing timeline. The testing process proves capable of checking elements that are not apparent to the naked eye. It can include BGA (ball grid array) packages complete with solder joints and connections. While a useful test, it requires an experienced and trained operator to carry out.
It is also prudent to remember that your electronic contract manufacturer will not necessarily inspect each board layer using the x-ray machine. Yes, you can see through to pinpoint internal defects. However, it is a tedious, expensive, and time-consuming process for ECMs and the client.
Benefits
- It allows for viewing hidden aspects of the BGAs and chip packaging besides their solder connections.
- Identifies underlying problems that are not possible to see optically
Functional Testing
Most electronic contract manufacturers perform a functional test for verification purposes that the electronic product will power up. It arises since most customers love this old-fashioned testing approach. The test requires external equipment pieces, fixtures, and requirements like MSHA, UL, and other quality standards.
A functional test’s parameters often get specified by the PCB consumer. However, some electronic contract manufacturers can assist with the development and designing of such tests. It also takes time and may not prove ideal if you need to quickly get your PCB product to the market. However, it can come in handy in saving face and money from a longevity and quality standpoint.
Benefits
- It saves a lot of money by eliminating the need for testing equipment
- Functional testing works effectively alongside in-circuit testing, flying probe tests, etc.
- It applies to a wide variety of printed circuit board types
Extra Functional Tests
Other functional test types can apply when checking a printed circuit board project based on the prevailing circumstances. The functional test can vary since a functional test aims to test and verify the PCB’s behavior when deployed. Aspects such as the PCB’s development besides procedures vary from one type to the other.
Other functional tests that apply based on the PCB variations include the following,
- Solderability tests. it ensures the sturdiness of the surface and enhances options for developing reliable solder joints
- Printed circuit board contamination testing
- It detects the bulk ionic that always contaminate your circuit board, leading to corrosion, among other issues.
- Peel test. It finds or determines the strength (as a measure) needed to peel off the laminate from the circuit board.
- Micro-sectioning analysis. It investigates the opens, shorts, defects, and other circuit failures.
- Solder float testing. It determines the thermal stress level the circuit board’s holes can repel.
Benefits
- It simulates the OE or operating environment and thus minimizes the cost
- It eliminates any requirement for costly tests
- The test can check the functionality of the product from 50% upwards of the product getting shipped.
- It pairs well in combination with other tests like flying probes and in-circuit testing.
- It detects false component values, parametric failures, and functional failures.