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How To Achieve The Best Possible Functional Testing For Your PCBA

On Mar 15, 2019

When it comes to outsourcing functional test system design and manufacturing for printed circuit board assemblies (PCBAs), you want to be on the same page with your test equipment partner before the design begins. It’s essential to have the detailed requirements identified so you can communicate your needs quickly and effectively to your partner.

So how do you ensure proper communication with your test partner? It starts with knowing what information they will need from you in the quoting process. Your test requirements may vary wildly, but there are some core considerations that will mostly likely pop up during any test design discussion. Here are some of the most common questions your test partner will ask you:

What functions does the device under test (DUT) need to perform?

The first step is to define the real-world application for the DUT for your test partner. You will be expected to be the expert on how your device works. The company you hire will be the expert on test system design. If you can document what needs to be done, your test partner will take that information and figure out how to do it. So, there will be questions around the power levels, voltages, currents, communication protocols, speeds, behaviors and more. They will also want to know what all the pins on the board do. A successful functional test cannot occur if you don’t define all the functions clearly.

What are the accuracy and resolution requirements for each measurement?

When your test partner thinks specifically about the type of instrumentation it will use to design your test system, the bandwidth limits, measurement accuracy, and resolution requirements needed for your data acquisition plan are crucial. The primary goal of the instrumentation system is to deliver measurement data to the end user in a way that’s easy-to-understand while also meeting your test plan technical requirements. So, providing clear direction in this area will minimize the chances for mismatches between your new instrumentation and the DUT environment.

As an example, in order to measure the rise/fall time of a switched current signal in a DC circuit, it is important to know as much as possible about the following:

1. DC circuit current nominal levels and range limits

2. DC circuit voltage nominal levels and range limits

3. Common mode voltage levels (if any) and any potential inductive noise injection

4. Rise/fall time range: seconds, milliseconds, or nanoseconds

5. Current sensing element physical size and location constraints.

What are the capacity and throughput requirements for the system?

Your test provider needs to gain insight into your manufacturing and/or testing process and how the system will need to be used. How many DUTs will need to be processed each hour? What’s an acceptable Takt time? How many total DUTs will you test each year?

Gaining clarity around the expected test capacity and throughput is vital before the test design starts. You want to create an understanding of your production needs so the system is designed for the expected durability and Takt time. Also, you want to give your test partner a clear sense of the automation that will be needed in the test environment. That way, the final tester will fit in well with your process.

What are the physical characteristics of the DUT?

To get test equipment designed properly, your test partner needs to understand the physical attributes of the PCBA itself. What’s the layout topology? Where are the DUT’s connections and how do you connect to it? What is your test access? Is it bed of nails or through the connector? Is it single-sided probing or dual-sided? Your partner will need these answers in order to properly test it.

Also, give your test partner a sense of the size of the board - its thickness and stiffness- and the part and test point density.

What are the conditions of the test area or manufacturing floor?

Provide details about where the DUT will be tested. The company you hire will want to build a test system that is compatible with the power delivery and air and vacuum supply in the test area. It’s also important to understand the thermal and humidity conditions so the environmental conditions in the test area understood.

Your test partner will want to understand how much space it has for the test system and any additional floor requirements. They will ask you about your safety and manufacturing standards (i.e. you can only use this type of electrical disconnect, or the tester must only be this color) so they deliver a system that works within these requirements. Clearly communicating your standards will help.

Do you have a statement of work (SOW)?

A concisely written statement of work will help eliminate ambiguity and frustration with your test partner and avoid any wrong interpretations of the requirements. If you are forwarding email chains and piecing together disparate documents, rather than delivering a polished SOW, you are jeopardizing the early design process. It’s easy to look past this step, but a good SOW provides incredible value in the process.

All these considerations will be an important part of the quoting process to get the right FCT for your PCBA test. If you’re ready to kick off a conversation to design a functional test, please contact us today.

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