Highly Accelerated Life Test (HALT) testing is completed on circuit boards, subassemblies, as well as the device or product level. System level HALT could be difficult in the event that system is physically large in size. Three problems exist. One, most HALT chambers usually do not accommodate large systems. Two, it can be hard to get sufficient vibrational energy into a sizable system to precipitate a failure. And three, temperature changes in the item within the chamber can be prohibitively long for efficient HALT. The only real place where HALT testing just isn’t performed has reached the component level. Accelerated life testing, as defined in Chapter 15, is the greatest solution to accelerate failures, identify failure modes, and discover reliability in the component level.
Additionally it is not recommended to perform HALT testing on a board that includes had a massive amount of engineering fixes, jumper wires, and glued components. The problem with excessive amount of rework is that issues can surface in HALT as a result of the quality associated with rework and not the caliber of the style and manufacturing process. Circuit boards which have excessive levels of rework must have the board artwork revised to add the design changes. It is advisable to consult design engineering following the prototypes are made to get an early on indication for the functionality associated with the prototype.
At some point in this phase, material will need to be purchased and assemblies designed for HALT. For expensive assemblies, it is best to hold off purchasing the costly items for HALT until there was assurance that the design works. This isn’t always possible if the items have long lead times, minimum purchase quantities, or high nonrecurring engineering (NRE) charges. If most of the material is purchased for HALT however the prototypes do not work, some of the material may well turn out to be scraped. The chance is greater on a brand new platform product than a derivative. Using material from another type of supplier for prototype and HALT may identify problems with a prototype part or procedure that is certainly not within the final product. In addition, some problems will go unidentified because issues with an element or manufacturing process cannot surface if it is not the main prototype process.
These problems affect the yield in PCB manufacturing, and also the manufacturer will fix them. The PCB manufacturer considers this area of the fabrication service and routinely “cleans up” your design. However, the supplier might not notify you associated with the fixes. Following the material is tested and discovered to be acceptable, it is transferred to a PCB manufacturer who will be applied for volume production. The design issues were not fixed into the artwork, so problems surface in production which were not identified because of the prototype. This type of problem could be avoided. Do not allow suppliers to create any changes into the artwork or perhaps the design without submitting a timely engineering change request.
There could be another problem with using different suppliers when it comes to prototype. Suppose Supplier A provides a quick‐turn delivery and is useful for prototypes. Supplier B is used for production. If Supplier A finds a challenge into the design and fixes it on his print, communicates it into the designer, but the designer fails to update his documents, then your problem may surface again in production, and you will have a scramble to figure out why. In PCB fabrication, manufacturers use different (often custom) software programs to check on for layout problems when you look at the board artwork. HALT should be performed on assemblies that are built utilizing the same bill of material due to the fact final product.