When introducing the need to create a Quality Plan with our customers, we usually get a combined look of confusion and fear. There is an inherent assumption that the CM will behave like a giant electro-mechanical 3D printer that can read their minds. This and several other major misconceptions can lead to quality failures in the field. Common assumptions include:
Even if teams apply good design practices to ensure robustness and manufacturability, the product still needs to be verified and validated that it meets their customer needs. A comprehensive test plan needs to be laid out very early in the product development system and aligned with the specifications, environmental conditions, use and abuse case, and life expectations.
Creating a comprehensive quality test plan is particularly useful during the quoting process, especially as it influences product cost, NRE, and technical capability of the CM. The quality plan then carries on through the life of the product to ensure that the product continues to perform as expected.
As you prepare for mass production, your CM will run a number of prototype and pilot runs. At each stage, you will have the opportunity to evaluate the performance and quality of your product and fix problems prior to the next pilot run. Engineering analysis, CAD models, and very early prototypes can be used to test the design, however some performance characteristics will only become apparent when you have production intent prototypes in hand. Time will always be very tight. Planning what you need to test long before the pilot run will help you identify weaknesses in the product quickly and make the design changes in time for the next pilot run. Your quality plan for these runs should include:
During mass production, your product will be subjected to a number of functional tests and other inspections. The could include tests of the Wi-fi chips, mechanical functions, power, battery performance, etc. Ideally, these tests developed and executed during the pilot runs. This provides the opportunity to find quality issues and as well as debug and optimize the testing process.
When you get the first prototypes in hand, you will have a very short window to identify and execute the design changes before the next pilot. Before the pilot unit arrives, you should have a comprehensive checklist of issues to look for. These can include qualitative assessments of feel and aesthetics and quantitative assessments of performance (such as, does Wi-Fi have the sufficient range?).
You will need to subject a certain number of units to certification and safety testing to satisfy the local laws and regulations (Click here for more in-depth information on the Certification of Hardware products).
Many of your parts will be made from molded plastic or metals. Making certain that the parts are of the right dimensions before the first build ensures that any problems can be traced to the design rather than the production quality. These could include:
- Durability, Environmental and Life Testing
In the normal life of your product it will get dropped, pulled, sat on, left in a hot car, kicked, sprayed with water, and collect dust. You will need to test your product to ensure that your design is robust to these stresses and can survive without impacting performance and safety.
- Transportation Testing
Your product will be subjected to wide temperature swings, impacts, drops and vibration before it even gets to your customers’ door. There are standard tests that ensure that your product and its packaging can withstand the stresses of being shipped and transported.
- Life Testing
Many failures occur only after a large number of cycles. Fatigue, wear, UV damage, and thermal stresses can have cumulative impacts on a design. In addition, some failures are random and just need enough cycles to ensure that the product has an opportunity to display the failure. Life testing runs the product through a large number of cycles on critical aspects of the design. Because the failures you are looking for are rare and random, a larger number of samples and cycles are needed than you think you need.
Once in production, your product will be tested at a component, sub-assembly, and product level. This ensures that the components are of the right quality, the assembly is done correctly, and no defects are introduced during the manufacturing process. These tests include:
When you buy components or sub-assemblies from suppliers, you can’t assume that their quality system is stable and capable. Each batch (and in some cases each part) will be subjected to incoming quality checks to ensure that the supplier is delivering a consistent quality that meets the specifications you have set. There may be special features or aspects of the purchased parts that you may want to do more frequent sampling if that feature is very critical to the performance of your system, or if it is a safety critical item.
Each of your PCBs will go through multiple tests including 100% optical inspection, in-circuit testing, and functional testing. You want to be able to find failures before they get built into your product and be able to diagnose a failure before you have to rework it (which may cause damage itself).
Your completed unit will have a series of tests that ideally ensure all functions work before the product is shipped. This can include camera tests, speaker function, etc. These tests are different from the verification testing. The verification testing will be much more extensive and often not possible to do 100% on the production floor. Functional tests will ensure that each individual devices works as expected.
You will have clear criteria about what is and isn’t acceptable to ship. These criteria can be as detailed as the size of flash and as seemingly obvious as no hair or sharp objects in the packaging.
Functional testing and inspection are not perfectly reliable nor will they catch 100% of defects. Mistakes may be made and defective units will occasionally get past Final Test. Shipment audits, executed by an independent inspector, take a statistically valid sample before shipment out from the factory and re-run a suite of functional and aesthetic checks. Any failures greater than the contractually agreed upon limits will require the CM to reinspect the entire lot and rework all failures found. It is critical to do this because it is very difficult and expensive to get product fixed once it leaves the factory.
Things change and degrade over time. Suppliers will make small changes to processes, second source suppliers deep in the supply chain will be changed out, SOPs change or aren’t followed. Running comprehensive reliability tests throughout the life of the product gives you a higher confidence that these can be caught before a large number of products are out in the field.
Often your CM will offer to help define the test plan - their expertise can be helpful in flushing out the details of the plan. As well, they might be responsible for developing the test equipment and executing many of the tests. That being said, the plan may not be as customized as you need - they will often cut and paste from old test plans, set protocols so the pass rate is higher, and will try to minimize their costs. It is quite common for the CM to underestimate the number of cycles required to effectively perform reliability and life testing.
The design of your test plan should always start with your specifications, requirements, product definition, environmental and usage conditions. If quality is currently an issue with your manufacturing, or, if you are just starting to address your plan, we are happy to answer any questions you may have on this very critical aspect of your overall success.
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