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In a previous article in this series, we discussed preparing for your first prototyping run and how you can cut down on lead times, as well as how to control costs with the right sourcing tools. Eventually, you’ll receive your new prototypes in the mail and you’ll need to test your boards in a real environment.
There are some important aspects of your prototype which should be tested. Your manufacturer will likely test the basic electrical connections once a board is depanelled and assembled, just to be sure that all the required electrical connections were made and that components fit into the right locations. However, they won’t test the functionality for two reasons. First, the functionality may not be known or obvious, and second, it’s just not their job. Once your board has passed basic manufacturing and assembly inspections, it will get shipped to you to check functionality.
Testing Your Prototype
Before powering up your board and running some basic electrical tests, it is important to note that your board might go haywire as soon as you turn it on. It is a good idea to hook up a multimeter between any exposed power and ground connections. If your multimeter reads 0 V between these points as soon as your board is powered up, immediately power it off. There may be a short circuit, or your power connection may not be soldered correctly. Check all important connections with a multimeter before proceeding further.
There are a number of other basic aspects of your board you should check that your manufacturer may have missed. It is also possible that you committed a design error, and your manufacturer was just following your instructions. In either case, you’ll need to identify any problems with your prototype by powering up your board and checking the following:
Board and Component Temperature
If this is your first prototype, you should check the temperature of critical components to make sure they are running at the appropriate operating temperature. Some active components (e.g., op-amp ICs) should be only somewhat warm to the touch while they are running. A component in a DIP package that is not a PLD should not burn your finger while it is running; if it does, then you may have hooked up the component incorrectly, and you should check your connections.
Active components like microcontrollers tend to run at higher temperatures when they are running at full power, and you’ll want to check the temperature of the board and the components themselves under these conditions. Manufacturers of these components normally specify that you should include a thermal pad and vias beneath the component to help dissipate heat, and this is your chance to check that these measures are providing the right level of thermal management.
No one wants this to happen to their prototype
If you included some thermal management features in your board, such as thermal lands and vias, then this test will tell you the effectiveness of these measures. Depending on the results, you may want to add some passive cooling to your components. In extreme cases, you may need to go much farther and incorporate active cooling into your device. It is also possible that you did not wire certain components correctly, or there is a short circuit somewhere in the board.
Fit to Enclosure
You’ll need to make sure that your board fits inside its enclosure in the way you envisioned. This is more than just a spot check; you’ll want to check that any electrical inputs through the enclosure have the right clearances, that power plugs or other connectors can attach to your device easily, and that the board fits snugly into its enclosure. You should always check to make sure that the board does not move or shift as you use your prototype. Your board should be mechanically secured to its enclosure.
Once the device is in its enclosure and the board is powered up, it’s a good idea to check the enclosure temperature. Placing the backside of the board is a good way to conduct heat away from a board with active components (think about how your smartphone gets warm when it has been run for awhile), but your enclosure should not have any hotspots. Unless it is absolutely critical that your board reach a specific temperature during use, you don’t need to measure the temperature. Instead, you’ll want to handle the board while it is powered up to ensure that it is not too warm to touch.
Short Circuits and Open Circuits
Once you board is inside its enclosure, it is a good idea to check for any open circuits or short circuits throughout the board. If you are using a metal enclosure, there is always the risk that you bridge power and ground if the backside of the board contacts metal. This brings up another design point: don’t place any solder points on the backside of the board if there is a chance it will come into contact with a metal enclosure.
Open circuits typically arise because a designer forgot to remove an extra connection from their board. It’s understandable, especially if you’re an entrepreneur that has been working on a new design until 2 AM every night. Any open circuits create a risk of shock when bridged. This is another case where you should probe your board with your multimeter to locate any open circuits.
We’ve all been up late bringing our ideas to life…
Compliance with Design Standards
If your board must comply with any design standards for your particular application, then this is your chance to check compliance. Your list of standards might be long, but the testing procedures will generally be specified in your standards.
Missing Components
There’s always a possibility that your manufacturer or assembler forgot to include a component, or it was not included in your bill of materials by mistake, or it was simply missing from your design. In any case, check the components on your board against your BOM and against your actual design.
Functional Testing in a Real Environment
If all the basic tests are passed, it is time to deploy your prototype in a real environment and check that it works as designed. Your goal should be to push your prototype to its limits in order to determine its reliability. This can include mechanical testing (try dropping your prototype and see if it still works!), testing in extreme cold or heat, and any other aspects you can imagine. If you did your homework and narrowly defined your design and testing requirements, then you will need to check your prototype’s functionality against all of these aspects. The results will inevitably inform any redesigns that may be required and will determine if another prototyping run is necessary.
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