PCB Test Point | Everything You Need To Know in 2024

Introduction

Without thorough testing, you can not expect your PCB to work well. The PCB testing will determine the quality of the PCBs.

You can establish an accessible zone for your PCB test probe by using a PCB test point. To have your PCB tested and certified by your supplier, you must define the correct test points on the circuit board layout throughout the design phase.

Testing the solderability and integrity of the elements on the PCB is a primary goal of establishing test points.  Many manufacturers overlook the importance of PCB test points. In this article, we will talk about PCB test points and how essential they are in the success of your circuit board.

PCB Test Point

Our circuit boards must also pass other tests before they are suitable for usage. The board is not only checked for functionality but also accurate assembly and readiness for use. PCBs include test points, which are small metal connections that allow for testing.

On a PCB with surface-mount components, a PCB test point is a tiny wire loop where test probes can be connected. Test signals are injected into the board’s circuit and monitored throughout manufacturing. Materials, shapes and sizes, and colors of test points are available in several combinations.

Test points allow you to choose a location where your test probe will have easy access. Several probes feature J-hooks on the end probes to support earlier PCB designs.

A PCB test point accommodates the J-hook. It is a sharp pointed tip that contacts a board conductor. Phosphor bronze alloy is the most common alloy used in surface-mount (SMT) test points. However, silver plate coatings can also be used, and they are also more affordable.

There are two primary purposes for test points, as follows:

  • The initial usage is in manufacturing. After the device is built, test points are used to assess its functionality. Defective items are discarded or sent to the relevant department to repair the PCB.
  • Even after a device has been sold to a client, it can fail at any moment in the future. The PCB test points are used to fix the device. These test points may also be used to re-calibrate your device if fixing is not possible.

The PCB test points are generally identified on the PCB and feature connectors or pins for attaching test clips.

PCB Test Point

PCB Test Point

PCB Test Point Types

On a PCB, two major types of PCB test points are employed. The first one is a net-connected tiny metal contact. The first is a place that a technician can readily reach using portable testing equipment.

These locations often include a soldered-in post for attaching a test lead to them to make testing easier. GND is a standard reference designator for such test points on silkscreen to make them easier to track.

To produce data sets for test automation systems, PCB CAD will employ their XY coordinates and net assignments to produce data sets for test automation systems. These methods can perform both continuity and solder connection and functional testing during PCB manufacture and assembly.

The other PCB test point is typically utilized for automation testing equipment. Through-holes, vias, or metal landing pads are examples of automated test locations on a PCB.

The PCB will be used by three primary testing equipment, each of which will make use of one or more of the test points:

In-circuit testing (ICT)

In-Circuit Test is a sophisticated PCB test tool. Using a bed of nails, ICT equipment connects directly to the test point and measures component performance independent of other components.

The use of ICT on the PCB test point enables the manufacturer to identify and fix any PCB issues immediately. ICT typically needs a PCB-specific test fixture.

In-circuit test (ICT) measures each component individually to ensure it is in the proper place. This kind of testing detects most issues on a PCB test point since most manufacturing flaws are short circuits or faulty components.

ICT simplifies flaw diagnosis, coding, and test result interpretation. Yet, it has downsides such as expensive equipment, difficulty updating mechanical test systems, and the inability to reach specific nodes in complicated circuits.

In Circuit Testing

In-Circuit Testing

Flying probe testing

In PCB testing, flying probes are the most often used approach. An XY grid is used by the probe machine, which was generated from the CAD files. The circuit board’s coordinate values are encoded into the device.

The needles are angled at a 45 ° angle as they descend. Connecting the probe to the test point requires two access points.

The value is determined by the system programmer, who then sets it. The machine then verifies this value.

Furthermore, flying probes are very precise. Using it, you may be certain that your final work will be error-free.  Double-sided boards can be tested as well. The probe has no problems testing one side of the board at a time.

Flying probe testing, like the majority of others, does not energize the circuit. As a result, you miss out on seeing your product in action in the real world that an ICT test provides.

A flying probe cannot examine the ball grid arrays. To connect to components, the prober needs access points.

If your order is big enough to warrant this approach, the cost is a concern. In the long run, the ICT test is a superior investment.

Flying Probe Testing

Flying Probe Testing

Bare board test

The test points on a bare PCB are tested for continuity and isolation. The continuity tests guarantee that no open spots exist in the circuits. It is a required step in the PCB manufacturing process.

In most cases, you can make improvements to the PCB test point design process using this type of testing. Bare PCB testing is precious during the early stages of development and has the greatest potential to save both money and time.

The bare board layout is used in PCB creation to decide where through holes and electrical components will be placed on the board. This circuit board substrate also defines the connections made by a completed board.

Bare Board PCB Test Point

Bare Board PCB Test Point

You can increase the dependability of your circuit board development outcomes by including bare board testing in your design process. This test is conducted after the PCB is built. This test is performed to ensure that all nets are connected electrically.

PCB Test Point Purpose

The objective of placing test points on a PCB is to determine whether or not the elements on the PCB satisfy the standards and are solderable. For instance, if you examine the circuit board resistance, the most basic technique is to use a multimeter to measure the resistance.

When they were first introduced on circuit boards, solder pins were utilized as test points for conventional plug-in (DIP) devices. The poor connection happens due to general electrical components exposed to wave soldering.

In large production facilities, you can not use an electrical meter to slowly check the board’s every characteristic.  These include the PCBs resistance, inductance, capacitance, and even IC circuits. This is why there is an automation testing machine for it.

It employs several probes to concurrently touch all of the elements on the circuit board that need to be examined. Program control is used to sequence and evaluate the properties of various electrical components side-by-side in a proper sequence.

The amount of components on the PCB has an impact. Several factors contribute to the final result. The more components, the more time it takes to test. In most cases, it takes no more than one or two minutes to test the whole circuit board thoroughly.

These probes may crush specific electronic components if permitted to contact them on the board directly. Or the probes may be destroyed during thorough testing.

So clever engineers devised “test points”: little round exposed metal points on both sides of components without a mask. In this case, there is no mask, which means that the probe may directly engage the electrical components to be monitored.

PCBs are becoming smaller over time as research & technology advance. Many electrical components are challenging to fit on a single piece of hardware.

At some point in the design process, the issue of test points taking up valuable space on circuit boards is brought up. Test points are likely to be round since the probe is similarly round.

Many needles need to be implanted at a time. It is best to build and make the next probe as near as possible to a single spot. The usage of needle beds for circuit testing is mechanically limited.

Probes and needles have a maximum and a minimum diameter, and the needles that are too tiny are prone to breakage and damage.  The spacing between pins is likewise restricted. Putting a flat cable welded on top of each pin is the best way to keep it in place.

Flat cable interference may also be an issue if neighboring holes are too tiny, so it is essential to consider that.   To avoid damaging the high section, the probe should not be placed too near it.

It is also hard to plant indirect needles due to the high portions as well as the test fixture’s needle bed base’s holes.

Test points are constantly being addressed as the board becomes smaller and smaller. Test jet, Net test, boundary scan, and other technologies may be used to minimize the number of test points.

AOI and X-ray tests can replace the basic needle bed test. But unfortunately, there is currently hardly any test that can completely replace traditional ICT.

PCB Test Point Components

Several companies produce and sell PCB test point parts. An instance from Keystone is presented in the next section.

A two-terminal component will be specified in your design, and it will be inserted in the design exactly like every through-hole component.  Additionally, SMD parts are available.

These elements are ideal for connecting a probe to a waveform to acquire measurements of it. Take note that there is only one connection point on each of these.

PCB Test Point Components

PCB Test Point Components

You may employ a direct probe connection for lower to moderate frequency (below 1 GHz) and rising times (over 10-20 ns). The low-speed electric buses (I2C or SPI) and GPIOs on the MCU make these parts excellent for operational testing purposes.

Keystone 5001

Keystone 5001

PCB Test Point Design Software

Historically, the process of creating printed circuit board test points design was entirely manual and required a great deal of effort. Since modern PCB designs are complicated, this approach is no longer feasible.

PCB Test Point Design Software

PCB Test Point Design Software

The majority of PCB design systems provide tools or capabilities to include test points in a layout. Before assigning test points, these instruments often require their settings set up, as seen in the figure above.

These parameters include a wide range of issues, including how near the test spots are to one another and the construction of additional criteria for testing. Manually or automatically, test points can be introduced to an early project phase after defined parameters.

Through-hole pins and vias are the most common locations for test points. The tools will allow the designer to create a unique via on a trace if no vias are accessible.

There are various choices for allocating test points, like inserting a particular reference designation or altering the via pad form from round to square.

The finest automated test point generating solutions are needed by PCB designers to keep up with their new product release timelines. Automated and pre-defined PCB test point spots and parameters are also included in this feature set to ensure that your manufacturer’s specifications are met.

You must use the most current PCB design software to meet the testing requirements of designs in today’s aspect. Additionally, Allegro PCB Editor or OrCAD includes a slew of additional tools to help you work faster and more efficiently while still maintaining high-quality designs.

PCB Test Point Design

A PCB test point should be an exposed conductive metal spot on an outer surface of the PCB which is linked to a network to operate correctly. This enables the automation testing equipment’s probes to establish contact with the metal plate and execute the test.

Some general principles you should remember before diving into the details of test point designing:

  • Your PCB should feature one test probe point on each node at least.
  • Component leads should never be used as test points.
  • The test points should be evenly distributed over your board. Component leads should never be used as test points.
  • The center-to-center distance between test pads must be kept constant at 0.100″.

In the CAD software, you will want to mark the desirable areas so that they can be tested later. Design  The design program will often identify test point candidates based on spacing and other factors.

The CAD software will export the data into a file once one candidate has been marked as the test point.

Strategies For Successful PCB Test Point

These guidelines will help you define and place test points on your PCB. Since manufacturers’ capabilities vary, designers must check these specifications before using them in their designs. To know how to choose a professional PCB manufacturer is critical.

PCB Test point sizes and dimensions

The bigger the PCB test point, the more efficiently the probe tips will contact it. The optimal PCB test point is 0.050 inches. However, most designers choose 0.035 inches.

Square-shaped test points are identifiable as test points and provide greater volume for the probes to contact. Most PCB design software includes automatic functionality for converting standard vias and holes to PCB test point terminals and altering their dimensions.

Spacing between test points

Less space between test points makes building, modifying, and maintaining the test fixture simpler. This is best accomplished using test points 0.100 inches apart from center to center.

It enables bigger, more durable probes, resulting in a more reliable test fixture over time.

PCB Test Point Spacing

PCB Test Point Spacing

Component spacing test

Spacing between components and circuits is minimized by using IPC component spacing recommendations. Depending on component spacing and PCB material, the drill hole spacing is very significant since it affects the operation of your circuit board.

The suggested clearance between the test point’s center and the component’s edge is 0.100 inches, with an actual minimum gap of 0.050 inches.

Another thing to remember is not to put larger parts on the PCB side edge near the probes. These may need extra machining and manufacturing stages, increasing prices.

Board to test point spacing

Often, test equipment employs a vacuum drawdown mechanism to bind the circuit boards to the fixtures, requiring extra space all around the PCBs periphery. For a satisfactory seal, maintain test points 0.125 inches from the board’s edges, with a threshold of 0.100 inches.

Test point location

To minimize high-density probing zones, arrange test points uniformly over the board. This clustering may cause the board to stretch and even destroy solder connections.

Keeping test points free of obstructions like overhanging components, mounting components, and solder mask is indeed critical. Furthermore, the PCB test points should be located to prevent forming antennas that transmit interference.

Parameters of the probe point

In contrast to automated test points, probe points have their own set of considerations. Their holes or surface mount pads must be big enough to allow the soldering post or loop to be soldered.

PCB Probe Point

PCB Probe Point

Identifying probe points

Thru-hole probe points may be marked as automation testing points on the circuit board’s backside, but they have a different use on the board’s top. These spots can be labeled in silkscreen with a reference identifier and a probable net.

Advantages Of Adding PCB Test Point

As we said earlier, the PCB test point is crucial for your PCB to function correctly. You will get these advantages if your PCB includes a test point:

Low profile

PCB Test point terminals have a significantly more discreet appearance when compared to other forms of test probe connections. PCB Test points are more adaptable than SMT components because of their identity profile.

Save time and money

Early testing points can save you time as well as money in the long run by identifying the connection issues in PCB. If you overlook this step, it may reveal problems in future design phases that include more costly assembly.

Easy defect identification

It is simpler to identify possible problems when using test point PCB in the probe testing procedure. The PCB Test point efficiently discovers your PCB problems by using a variety of testing methods and techniques. This enables you to resolve the issue with your PCB in a short period of time.

Reduces rework on PCB design

The PCB oscilloscope test point identifies the circuit issue of your PCB. It provides you with instructions on how to make your PCB function correctly.

The PCB test point guidelines help you decrease the amount of time you spend reworking your PCB design. Every time, it allows you to build the best PCB design.

Reducing rework on your PCB design is game-changing. It saves your time, effort, and money in the long run.

Conclusion

A good design with evenly distributed test points ensures your product’s reliability. A PCB Designer must have complete knowledge of test points to avoid any kind of complexity in the design or the later fabricating, manufacturing, and assembly of PCBs.

PCBMay ensures your PCB safety by professionally designing the test points. In order to ensure that our PCBs will operate the same for years to come, we conduct rigorous testing.

Please do not hesitate to contact us if you have any queries about the PCB test points or get a quote. We make every effort to respond to each and every one of your queries.

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