I work for a large medical device maker where I focus on manufacturing electrical test at the circuit board level. When I think of test engineering it comes down to instrumentation, measurements and automated test systems. I’d like to expand my view of what is, sort-of is and isn’t test engineering in a way that other test engineers can agree with.
What test engineering is not
Software testing is not what test engineers do because test engineers tend to have a background in electrical engineering or as an electrical technician. Software testing is something that computer scientists do (or probably don’t want to do).
Software development / Software engineering
Test engineers do a lot of programming but they are not software developers. The code that test engineers write is really more like scripts to control instruments and take measurements.
Design verification testing
I don’t really think of design verification as what test engineers mainly do. Test engineers focus on testing products during the manufacturing process. Testing that the design does what it’s supposed to do is what the design engineer does.
What test engineering (sort-of) is
At a large company there will be quality engineers or a whole QA department. They do things like analyze products for failure modes and track product failure trends. They might be the people who ask the test engineers to implement new test methods or test coverage to detect a newly discovered failure mode. They will commonly do more data and statistical analysis than test engineers. They also will focus on predicted reliability of a product and analysis of returned field product.
This job is more often overlapped with the job of the test engineer but again at a large company they are usually separate positions. The manufacturing engineer focuses on taking the tests software and systems developed by the test engineers and deploying them to the manufacturing floor. They will focus on the yield of the product being tested and making sure that the test systems are working and under control. Under control is a statistical method of looking at the measurements a test system is making to be sure it’s still measuring correctly. If one device under test fails it’s probably a bad part, if nine out of the last ten fail, something has gone wrong with the test system.
What test engineering is
TE is all about measurements and automated test systems to make measurements on products on the manufacturing floor. Depending on the test strategy being implemented, electronics may be tested in all or some stages while being built. Testing may take place on the individual components, integrated circuits, PCBs and finished products.
Components may be tested by a vendor, sampled and tested or 100 percent tested before they are used in a product. Large companies often have people other than test engineers working with component suppliers to determine how their components are tested and manage that relationship.
Integrated circuit testing
Integrated circuit testing is a specialty of test engineering that is the most complex and costly of the testing. This is often performed by the chipmakers themselves or outsourced due to the high cost of buying “big iron” testers. A company like Teradyne focuses on building extremely expensive and large test systems for integrated circuits.
Testing a PCB can be a very flexible place to perform testing. With a PCB there is still access to the circuits through test pads (this isn’t always true with some products being so small, there is no real-estate to spare for test access or boards are multisided) and also access through techniques like BIST and Boundary Scan. Also, it’s still cheaper to find a problem with a PCB than find it with a finished product that won’t turn on. Since it is so flexible, how a PCB is tested is variable. In my industry there is often a bed-of-nails type DUT interface along side a test system. But, the list of variables include, cost, volume, PCB complexity, application and level of regulation. This all gets to test strategy, which I plan to write about in the future.
Finish Product (functional) testing
Functional testing is a somewhat broad term. It could be interpreted to mean that when you power up and operate an electronic product it simply works or it can mean testing some higher-level functionality at a lower level. For example, while still at the PCB level a product could have sub-sections of the system functionally tested for some higher level measurement like the bandwidth of an amplifier. Another way to think of it is once you lose any access to the system, like probing test pads, and the product is complete then functional testing is taking place.
It’s worth mentioning that inspection is slightly different than testing. Testing is where a product is built and then it is measured to determine if it is has defects or functions correctly. When a product is tested and it doesn’t work, there is no going back, you either scrap it or repair it. With inspection a product is observed to check for defects so it can be caught earlier. For example, you could test a completed circuit board or you could inspect an unpopulated PCB to look for a broken trace so all the time and expense of populating that PCB with components can be saved.
I mentioned that reliability activities are not always the job of the test engineer. That might seem a bit strange, but really there is a difference between testing a product to see if it is working right now when it is shipped, versus attempting to perform tests to try to predict if a product will continue to work for its expected lifespan. These types of activities would be considered reliability testing. One such type of test would be a burn-in test, where the product is tested in a high temperature environment in an attempt to remove weak products. Incidentally, just testing something at high temperature doesn’t reveal many latent problems. What is much more effective is to test in a temperature cycle, forcing the product to experience the expansion and contraction stress. Humidity is another important environmental variable in determining reliability.
There are a lot of issues to consider and steps in the process of testing electronic products. I have gone over it really fast in an effort to establish the basics without going into a lot of detail. I’ll dive into many of these topics in more detail in the future and hopefully I won’t miss too many important considerations in test engineering.