I wish the article had explained eliminating lead from solder used in electronics equipment is a European Union requirement under RoHS that has no counterpart in the U.S. Unfortunately, the leads or conductive portions of most component parts are now tinned in almost pure tin - from which grow tin whiskers that cause shorts.
It all depends on your tolerance for failure.
It also depends on what the the contract allows. Always check there first. Than, before you commit anything to your CAD/Drafting department, TALK TO YOUR FRIENDLY NEIGHBORHOOD COMPONENT ENGINEER. It is his/her job to keep your parts selection within the parameters set by the program.
P.s. I have a lot more to say on the subject. A lot more, but I would be exceeding the limits set by EETimes. So this is my "tweet" response
As an engineer with twenty years experience in military avionics power supply design I whole-heartedly agree with the author. I also know well the basic concept of COTS. Most program managers pick a COTS solution to avoid the NRE on a custom design. Then once it gets into the field, they end up paying the price when the part, such as a COTS power supply, doesn't work and no one knows anything it. The company that they bought it from either no longer exists, wants a lot of money to fix it, or they don't know how to fix it either. I have been down that road before. Custom designs in-house cost more upfront, but they save a lot of money over the life of the program, bank it.
Thanks for taking time to comment. I'm definitely interested in understanding where you see a disconnect. My understanding of commercial off-the-shelf (COTS) has always been just as the name suggests – they constitute a standard, commercial product line designed to meet a standard set of specifications for applications across a broad range of markets. A COTS linear regulator, for example, might be used in architectural lighting, consumer electronics, and automotive designs. The broad customer base generates volumes that keep prices down. The devices may not literally be available off the shelf, but they are rapidly available. I consider commodity components to be a subset of COTS components. Commodity components are economical, available in volume, and basically vendor independent. COTS components are economical, available in volume, but are not necessarily as interchangeable.
Does that fit with your understanding? If no, how does your definition differ?
The problem I was trying to highlight in this blog, which I have heard about from the customer and vendor side over and over, is that consumer markets move quickly, and carry manufacturing with them. If a COTS component has been aimed at a specific market sector such as cell phones or digital cameras, and now that demand has evaporated because the latest generation of those devices imposes new requirements, the COTS component vendor will most likely move on and begin producing new products for their volume market. As far as they are concerned, in the context of their customer base, the older component has become obsolete. Continuing to produce it is no longer cost effective. In a perfect world, a similar device might be available from other vendors, but there's no guarantee that they will satisfy all of the specifications required for, say, a replacement MCU deployed in a Humvee built two years ago.
Do you agree? Disagree? Please drop me a line and let me know.
Thanks for your response. You are correct, I should have added more detail on the Reduction of Hazardous Substances Directive (RoHS), which was put in place in the European Union in 2006. (I'm still trying to catch up with how much detail I need to provide in these blogs. (Note to self: that would be more))
So, a quick explanation of RoHS. Designed to reduce the amount of toxic substances released into the environment, RoHS sets maximum levels for six controlled substances: : lead, mercury, cadmium, hexavalent chromium, poly-brominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE). In order to sell into the EU, manufacturers need to demonstrate that their products comply. In the case of electronics, that has led to manufacturers converting from lead-based solders to tin, which carries the aforementioned risk of tin whiskers.
As you pointed out, RoHS is a European standard, which means COTS components bought and sold outside of that sound do not need to comply. That said, today's manufacturers play in a global marketplace. If they want to sell into the European Union, they have to comply with RoHS. That gives them the choice of either developing and supporting two product lines/process lines – one leaded, one lead free – or a single lead-free line that produces devices to sell into both marketplaces. It's understandable, if frustrating, that many manufacturers elected to go the easier route. Yes, it has ramifications, but mostly for a small subset(mil/aero)that is not the primary market for most of these vendors.
And that brings us back to the unfortunate issue of how market dynamics can create issues with the use of COTS components in mil/aero systems.
Let's review the bidding that got us to where we are today... During the Reagan era, it was hang the expense, makes lots of military stuff to bury the Soviets economically. COTS happened starting about the 1st Bush era, and was to try to control the extreme costs of meeting a bunch of very over-blown and over-grown requirements that were often based on issues with old technology being placed upon any new design. Then and now "COTS" systems were generally not pure "commercial", but ruggedized and carefully-parts-chosen designs to keep the military skeptics at bay (yes, I was also a submarine officer in a prior life). To expect a true "commercial" design to perform for a 20-year product life in a military application at the rate of technology change today, while not funding and supporting cutting edge R&D and product releases, is a total pipe dream.
As regards RoHS, some of the first lead-free solder was developed for military and space applications, based on Indium alloys. These alloys, albeit painfully expensive, are still available and in use today. Several manufacturers can readily adapt to Indium based paste for board assembly, but you definitely won't get cheap made-in-China real-commercial board assemblies made that way. I was also rather surprised that the discussion of tin whiskers did not include a side-note about gel-potting and conformal coating use to limit this effect, nor a discussion about clearances and circuit lowering of voltages that can be used to reduce this effect. I do understand that QFN and BGA packages make both of these techniques a little limited. However, a modern SMT package that is designed specifically for aqueous cleaning beats the socks off a metal-ceramic-frit "hermetic" package in cost and availability.
If obsolescence in 5 years is considered reasonable with IDS-based black-box replacements regularly procured as technology progresses, there are still a lot of options out there. I used to work for a large Peoria manufacturer that expects a 5-year life out of in-house and customized designs used on heavy equipment, and makes plans for obsolescence of parts and assemblies. The need here is for the military to make up its mind, "Do we require gold-plated hermetic everything electronics that we are willing to pay manufacturers to continue to produce well after the technology lifetimes of several of the parts involved, or do we want relatively inexpensive and slightly less reliable equipment that we can afford?"
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