Implementing PCB Test Point Guidelines With OrCAD X

Key Takeaways

• Test points should be placed based on what is being tested and how the test will be performed.

• Although test points may be of various shapes, they can be classified as being either for manual or automatic testing.  

• OrCAD X tools help you easily define specifications and place test points and other vias.

Circuit board ready for testing

Testing is the third leg of the circuit board design⇒build⇒test iterative development cycle, but it’s just as important as the other two. In fact, failing to test can result in deploying PCBs that fail to meet their operational and performance objectives. These costly contingencies–if redesigns and/or recalls are necessary–can be avoided by following good PCB test point guidelines. 

Important PCB Test Point Guidelines

The questions above should be asked for each test point. The answers provide the information to guide your location and dimension specifications.  

Typical Test Point Specifications

How a test point is specified during PCB layout design primarily depends on how the measurements will be taken. Important specifications to consider include:

When implementing these test point items, it is important to perform design rule checks for constraint compliance to avoid redesign and unnecessary board respins.  Another important determining factor for effective PCB test point guideline specification is the type of testing that will be performed.

Types of PCB Testing

There are two main types of test points used on a printed circuit board. The first is an easily accessible point that is accessible with manual testing equipment. To help with this, these points may have a post soldered into them for clipping on a test lead. These test points will be marked with a reference designator and usually the name of the net in silkscreen for easy identification, such as “GND.” 

The other type of test point is used primarily for automated test equipment. The automated test points on a circuit board are thru-hole pins, vias, or small landing pads of metal that are designed to accommodate the probes of automated test systems. There are three main test systems that will use these test points on the board:

• Bare board test: This is a test that is run after the circuit board has been fabricated to make sure that all of the nets in the board have electrical connectivity.

• In-circuit test: ICT is run after the board has been assembled. The board is positioned on the ICT fixture which is filled with probes for each individual net. These fixtures usually test the bottom of the board, but they can also test the top or both sides together if needed.

• Flying probe: Like ICT, this test is run after assembly on each net of the board by accessing the test points. Where it differs, however, is that the flying probe equipment uses two to six probes that move around to each test point instead of using stationary probes in a fixture like ICT does.

Circuit board measurements taken with a flying probe tester.

Efficient Test Point Design With OrCAD X

When used, test points are important elements of your PCB layout design. However, it is critical to consider and follow PCB test point guidelines that are based on particular use cases. Ensuring your test point specifications meet placement accuracy and spacing and clearance adherence rules is required for manufacturability. How well you satisfy these objectives and do so efficiently depends on the functionality and capabilities of development software. 

The OrCAD X PCB layout environment, shown below, is designed to help you optimize placement, routing, and adherence to critical DFM rules to ensure your board is buildable and satisfies industry standards for test points, as well as other PCB elements. 

OrCAD X PCB layout U

As shown above, the PCB layout environment in OrCAD X gives you autonomy to create your own workspace to facilitate efficient board creation. This includes easy modification of all visual enhancements, straightforward and customizable editing tools, and same-view access to important elements and board information. Creating the most ambient innovation environment for incorporating design criterion like PCB test point guidelines is simple with the new OrCAD X platform. Moreover, you can integrate with any Cadence advanced PCB Design and Analysis solutions.