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Smart Tests

Did you ever receive circuit boards that did not work as expected, and you do not have a clue why? In the traditional electronic industry usually only ⅔ of the circuit boards survive an electrical test. But did you know that with a few design tweaks you can improve the survival rate immensely?

Manufacturers are cagey about providing detailed test information as this could reduce their workload. Instead, they let you work with an imperfect design which will crash in series production later.

Not with us. 100% of our Beautiful Boards are electrically tested. With our Smart Tests we provide you with a detailed test report of your order directly after production. This gives you a fantastic opportunity to identify and improve weaknesses in your design.

About this article

This article explains everything you need to know about our Smart Tests. You have received a faulty test report and are now wondering what to do next? Or you are simply curious and want to learn more? Then you have come to the right place.

Basics about E-Test

Unlike many other products, where a complete check of an entire batch is too costly and/or would lead to the destruction of individual products, the high efficiency of today's flying probe testers enables a complete electronic check of each individual board before it leaves the manufacturer.

The test procedure is always identical: For each measurement, two different measuring points are approached simultaneously by two probes, a potential difference is applied, and the resulting resistance value is measured and documented.

But how does the flying probe testing machine “know” between which points to measure and how to interpret the results?

The basis for the test program is formed by the nets and pads defined in the respective PCB design, which are derived from the circuit diagram. They determine which points must be conductively connected and which must not.

Pads are designated and exposed surface areas which allow to solder or mount components onto the PCB. A net is a group of pads that are conductively connected to each other.

The logical connection between nets and pads is hereby as follows:

All pads of a net must be conductively connected to each other. Conversely, pads from different nets must not be connected. This logically also leads to the fact that each pad can only belong to one single net.

During a test run, both pads of the same net and pads of different nets are approached. Our Smart Test checks for open connections or short circuits.

OPEN: The measured resistance value exceeds a defined limit value for pads of the same net.

SHORT: The measured resistance value between pads of two different nets falls below a defined limit value.

IPC-D-356 and Gerber

Unlike the other PCB data, this detailed test information is not written and transferred in Gerber, but in a standardized IPC-D-356 format. We automatically extract this file from any CAD file when you upload your project to AISLER. If the file is not available, e.g., because only the pure Gerber data has been uploaded, the Smart Test Service is unfortunately not available.

As already mentioned, the logical relationship between the listed pads and nets in the IPC file is based on the schematic in your CAD application.

For a meaningful test, it is therefore necessary that the schematic has also been completely implemented by the developer in the corresponding PCB design.

Test data and PCB design must match before manufacturing. If two pads of the same net are already not connected to each other in the original copper layers, an open connection will certainly be detected in the e-test. In this particular case, there is no manufacturing defect, although the test result in itself suggests otherwise. It was merely tested "incorrectly" based on the board design, respectively the Gerber data. From the point of view of the circuit diagram, an intended connection was not implemented. In such a case, it is up to the developer to decide whether the design produced in this way is functional or whether an adaptation of the design and a remanufacturing is necessary.

How to read the test report?

As you may have noticed, the minimum order quantity at AISLER is three PCBs; larger quantities must always be multiples of three. This is because a batch always consists of three identical panels. Depending on the size of your order, we may also have to split it into multiple batches.

For example, if you have ordered 27 PCBs, each panel will normally contain 9 instances of your PCB.

9 PCBs (instances) / panel × 3 panels = 27 PCBs

After production, each panel is electrically tested, and the Smart Test report will be attached to your project and will be visible under Tests. We will also inform you by mail as soon as the results are available.

The test results are sorted by panel and instance. Normally, three test results should thus be available for each batch. Please note, that we only display detected defects.

The following picture shows an exemplary test report of an order. You can see that all three panels (Run 2, Run 3, Run 4) of the batch were tested. However, issues were only found on one of the three panels (Run 3).

Smart_Test_Result

In this example, 15 PCBs were ordered in total. This means that five PCBs were placed and manufactured on each panel. Since the PCBs were very small in this case, we combined five of them into one subpanel. This subpanel got the internal instance number 36. The net names were further indexed to enable differentiation within the subpanel.

Just one board of the subpanel is affected (GND_2 = index 2), as only nets with index 2 are listed in the test report. In total, 14/15 are error-free.

How to interpret the test results?

If there are no issues: Amazing! Everything went well during production. This also means that your design is perfect to manufacture. Good job!

If errors are found in your order, there is no reason to panic! In many cases, the PCBs themselves have been manufactured correctly and the detected errors can be traced back to deviations between test data and PCB design.

In any case, all boards will be sent to you without any impact on the dispatch date.

Before you start measuring all the affected connections of the boards, we recommend that you take a closer look at the Smart Test results. Often, the type of defect, the defect consistency and the frequency can already be used to assess whether a manufacturing defect is likely or not.

Identical opens on all PCBs:

Please check your design first. It looks like the manufacturing data deviates from the test data.

If everything seems fine and on each panel is just one instance: Please wait for the boards and check if all visible vias in the BoardViewer are correctly manufactured.

Identical opens throughout every panel, but only one instance is affected:

This could be an indication of a manufacturing defect due to one or more missing vias. Please check the boards after the receipt.

Identical shorts on all PCBs:

Please check your design first. It looks like the manufacturing data deviates from the test data.

Shorts and / or opens are randomly detected on one or more instances:

This is an indication that one or more boards have not been manufactured correctly. Please inspect the PCBs optically.

This may be due to a conventional manufacturing defect. However, you should also check whether your design complies with our Design Rules before reproducing it. The cause may also be in the design, which is difficult to realise from a production point of view (e.g., with exceptionally long and thin trances). Please also have a look on our Ultimate Guide to a robust PCB Design.

My PCBs were manufactured incorrectly. What happens next?

We are sorry if we have made a mistake here. In this case, please use our contact form and describe the problem. We will do our best to identify the cause of the error and find a quick and satisfactory solution for you.