Assembly/product reliability - Page 1
Forum section: electronics / projects

author: Mecanix
author_rank: Frequent Contributor
timestamp: February 20, 2021, 11:08:37 pm
content: Hey guys, what are the processes that electrical engineers generally put in place to ensure product reliability before manufacturing?Particularly in the fields of thermal management and of course vibration & impact testing?First off; is this the EE's job? or that's normally outsourced to the m.eng dept or ?

author: Tomorokoshi
author_rank: Super Contributor
timestamp: February 21, 2021, 03:05:03 am
content: This topic can get very large very quickly. Just to get a sense of scale:1. Is this product:1.1. A circuit board in a box that sits on a table in a hobbyist's basement?1.2. A circuit board that goes in a high-volume consumer product?1.3. A control board in an industrial machine?1.4. A control board in a vehicle?1.5. ...2. Is your team:2.1. You only?2.2. You and a software engineer?2.3. You as part of a team of a few people at a startup?2.4. You as part of a team of 10 in a company?2.5. You as part of a team of 100 in a large corporation?2.6. ...3. Is the volume:3.1. 1's3.2. 100's3.3. 10,000's3.4. 1,000,000's3.5. ...4. Is your project budget:4.1. $1004.2. $10,0004.3. $1,000,0004.4. ...5. Is your project schedule:5.1. Weeks5.2. Months5.3. Years5.4. ...6. Does your organization:6.1. Work using common industrial standards?6.2. Have a group that deals with ISO 9000, etc.?6.3. Get certifications for other products?6.4. Sell internationally?6.5. ...7. Is your management:7.1. Interested in quality?7.2. Interested in speed?7.3. Interested in cost?As for the EE role; now it gets interesting. That really depends on the personality and experience of those involved, the scale of the organization, etc., including:- Electrical engineers- Mechanical engineers- Technicians- Management- Manufacturing- Quality control- Sales- Marketing- Legal department- etc.Is it the EE's job? That's tough. You could be in one of several situations:- The task is given to you even though you think it's outside of your experience, qualifications, job description, etc.- You see the task needs to be done but those responsible for it are not taking it seriously, etc.- You see the task needs to be done but there isn't anyone else to give it to.- The project has schedule or cost pressures that makes distractions like quality get skipped.As for your specific questions:Thermal ManagementIs this in regard to heat sinks, fans, thermal deration, etc.? If so, then if falls into the EE area for a lot of the work. If you have a mechanical engineer you can work together on the problem. It may take a lot of your to get them up to speed on the idea. Mechanical engineers may make assumptions that don't square with reality or practice; just because they might sound confident doesn't mean it's right. Make tests and collect data. Note that you need to be very careful about the test methodology to make sure you are measuring the right thing.Vibration TestingVibration testing can be done in special machines that shake the equipment through some thermal and acceleration profile in all 3 axes. Likely internal only for larger corporations. Knowing what is acceptable will come down to the type of product. Guidance can come from applicable industrial standards.Impact TestingImpact testing also has standards that cover it. Or, it might be not much more than dropping on a certain type of floor from a certain height.

author: Mecanix
author_rank: Frequent Contributor
timestamp: February 21, 2021, 07:18:37 am
content: Thoughtful and quite relevant. Thanks, Tomorokoshi.Recently seen rather traumatizing failures particularly at the joint level caused by just a few hundred thermal cycles and warpage effect. Picture a powered PCB mounted into an enclosure at four or more 'fixed' points, looking smart, but disregarding the 734,006 million-billion different materials' thermal expansion coefficients and the stresses/orientations. Yet at the natural freq, vibration & shock tests.I'm keen on learning and gearing-up for the job(s) having half-relevant exp in co-sims and tests fixtures, however less keen of fulfilling the Legal Department role, if you get my drift. That's why I'm curious as to how its done on the commercial / EE professional level. Probably a better ROI with a solid insurance policy some will say to that.Regardless. Are we following Test & Validation Standards from JEDEC's, IEEE's, ISO's, MIL's, Others? Who is The Voice in your EE industry? Please take me to your leader...

author: wizard69
author_rank: Super Contributor
timestamp: February 22, 2021, 05:49:42 pm
content: Quote from: Mecanix on February 21, 2021, 07:18:37 amThat sucks!QuoteYou didn't go into detail but I'm guessing that in your case this will be the responsibility of an electrical engineer if your organization is no large enough to employ somebody specialized in thermals. One thing to consider is what do similar products do to handle the problem you are seeing. Since there is no info here I can only guess that there are similar products on the market, but often the school of hard knocks has taught other people what not to do.You verbal picture of the board does nothing for me nor do you really go into the functionality or how it is used. One thing I've seem multiple times is that the end user will assume one thing that maybe the designer didn't intend often leading to excessive current draw through a product. Often the initial design is not technically wrong but rather didn't anticipate the user. This is where good technical specs and limits of operation can save your butt.An example here from the real world. If you know what vibratory bowls are you know that they can oscillate intensely. Mounting your electronics control panel to the frame of such a machine can be a very bad thing for the electronics. Stuff literally rattled apart. Terminal strips IDC connectors and motor controllers, just about everything came undone. This is a failure you rationally can't blame on the electronics however well specified data sheets can keep you from being held responsible.Obviously I don't know if your issues are user caused but I just needed to point out that not all early failures are the result of incorrect design. It looks like in your case though you do believe that these failures are indeed design related.

author: bdunham7
author_rank: Super Contributor
timestamp: February 22, 2021, 05:59:52 pm
content: Quote from: Mecanix on February 21, 2021, 07:18:37 amPerhaps the practice of using SMT power devices without fully considering the ramifications of using the PCB as a heatsink or even doing the math or planning for adequate margins is an issue? Reliable, complex boards have been around for a long time, so there must be a reason like incomplete engineering or cost cutting, which are perhaps the same thing sometimes.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: February 22, 2021, 06:44:42 pm
content: https://www.weibull.com/hotwire/issue70/relbasics70.htm

author: Tomorokoshi
author_rank: Super Contributor
timestamp: February 23, 2021, 04:19:18 am
content: I haven't done much that required very careful thermal design. I've only had moderately careful thermal design. Many of these may not be applicable due to some design constraints of yours. Of the things I've seen over the years:1. Allow for expansion.2. Allow for flex.3. Separate high power / high temperature from low power / low temperature using cabling.4. Use heat sinks with proper airflow.5. Change the design constraints.6. Test sub-systems or components independently of the rest. This may require a few expensive iterations. Might be cheaper in the long run.7. Get a bunch of thermocouples and readers. You will want at least 8 channels for a moderately complex design. Instrument using relatively controlled conditions. Collect data. Back up iterations with data. Make the mechanical engineers do their job by designing parts to meet your needs. They'll complain about the "parts tax", machine time, etc. You will need to navigate through that somehow.8. Get a thermal camera. A good one. How much are your field failures costing you? Can you afford a $10,000 thermal camera? It will pay for itself. ROI against warranty, design iterations, engineering time, time to market, etc. in order to get management approval.9. Get access to something like this. Dig around their web site for information on standards, methods, etc.:https://espec.com/

author: jonpaul
author_rank: Super Contributor
timestamp: February 23, 2021, 04:54:18 pm
content: Hi there Mecanix:In 50 yrs I have seen a few things of possible interest:Damaged units due to poor shipping package designPotted units DOA or fail early due to chemical reaction and mechanical stressPoorly specified power components, insufficient thermal data used to designFailing line filter caps X and Y typeICs fail due to aging and thermal cyclingSwitch and connector contacts fail or oxidizeSystems blown up due to mismated connectorsHigh voltage pulses from other system sections or external inducing IC failuresCreep and track of transients causing arcs on PCB due to insufficient clearanceTantalum capacitors failing shortedTransformers overheatingPrediction of reliability is in basic texts and courses.Essence: Ever 10 deg T rise doubles all aging and chemical reactivity.Fail rate is a bathtub curve, like for people:highest at birth and early life, settles to a low minimum for most of lifetime and rises near death.So testing at elevated ambient can predict some weak points.For REAL reliability check the old Bell System/Western Electric Central office and long haul transmission designs, 40 years lifetime.Also the 1970s-1990s HP and TEK equipment with NO LCD, digital and gold plated US made FR-4 PCBs and gold plated connectors.Just the ramblings of an old retired EEBon JourneeJon

author: Mecanix
author_rank: Frequent Contributor
timestamp: February 24, 2021, 05:20:24 am
content: ^^ Right, I see now, Jon :/ So you're saying failures are as dynamic and random as the weather in electronics, and trying to prevent the worst is lottery odds-like. Not exactly a good start!!!Thanks to all of you for sharing invaluable pointers and guidance, some great minds and impressive knowledge here obviously.Look. We're a tiny-micro-miniscule family owned SME with now 7 staffers and have a product line with focus on motorsports (performance aftermarket parts). As our designs & assemblies evolves (and so is the tech) we see a need for embedded sensors, data acquisition, dynamic performance tuning and obviously, all its relevant mfg bench fixtures & validations. All in all, some involved electronics (if not all) will be subjected to rather harsh environments and therefore needs to be engineered, so to speak. So.. that's that.We've recently upgraded our software license from a structural linear/non-linear, fatigue and response dynamics and added a complete M/ECAD & CFD solution (Adv Coupled Thermal & Flow). ps. this structural 'digital-twin' validation allowed us to save monumental amountof timeand money and efficiently helped us to achieve nearly 90~95% success rate with real-life prototypes.With that out of the way, I guess what I'm really asking is; does our EE have similar modern workflows when it comes to thermal management and vibration/impact testing? aka how is this being validated before real-life prototyping?pps/side note. you wouldn't believe the difficulties we are having finding out about isotropic & orthotropic material properties that the popular manufacturers use for the products they sell, scandalous almost. Even when asked they either ignore the request or tell you off with pretext of nda and other complete non-sense. Wish I'd be joking here but I'm not, but that's for a whole other topic on its own I guess...

author: Mecanix
author_rank: Frequent Contributor
timestamp: February 24, 2021, 06:11:40 am
content: Quote from: wizard69 on February 22, 2021, 05:49:42 pmIt actually does. Not mine though (see attached research paper where my comment/trauma originated from). My assemblies never-ever fails and as bullet proof as anyone can hope for(rolleyes). I wish though, and hence why 2021 is all about gearing-up in both practice and knowledge on the subject of co-sims and validations.Source:https://rc.library.uta.edu/uta-ir/bitstream/handle/10106/25099/MahesanRevathi_uta_2502M_13156.pdf

author: poorchava
author_rank: Super Contributor
timestamp: February 24, 2021, 09:06:07 am
content: IMO this depends mostly on the price sensitivity of the end product and the volume/margin.My deal is specialist T&M gear (mostly power industry) in my day job and mostly industrial/building automation & UAV electronics as the side gig.In general the more price sensitive the product is, the more effort and at lower per unit cost you need to put into achieving required reliability. And the volume must be high enough that the effort makes sense. If the volume is lower, margin better and more focus is on minimizing NRE, then overengineering is my way to go. With specialist gear, the price is negotiated with customers separately anyways.Obviously application also matters. Portable and handheld stuff can be subject to some really dreadful events. If your products just hangs on a wall and has to pass certain standard tests, and you'll probably be fine. If it gets manipulated constantly as a part of normal usage scenario, you wouldn't believe what people can do to a product. No standard will prepare you for that. You need to find a line between 'lets make this robust' and 'f*** you, bring it for a paid repair'.For example we found out in my day job, that the most common reason that heavier components get ripped of the PCB, if users literally pounding the damn 1000€ handheld instrument against a table when they see a 'low battery' indication. And in some cases these were people that paid for the poor gizmo themselves. Of we only adhered to standard mandated tests, the warranty and repair indicators would go through the roof.Automotive stuff is (sometimes surprisingly) incredibly price sensitive. I recall working for a well known T2 automotive company (eg making boxes that go into cars made by T1 company) and we were told, that out customer's (very known luxury car company) CEO demanded a 30% price drop on a 15€ box that went into VERY VERY expensive car. And they were completely adamant they they absolutely require that price drop 'or else'. That's when you put dozens of hours into figuring out how to do certain things cheaper, or figuring out how cheap we can go. Also, the specs for things are often settled on non-engineer level, and you end up with stuff like 80A traves going across a 200x200mm PCB or having to design a box to 110*C working temperature, because they couldn't find a different spot for it on an entire truck, than 50mm from a hot coolant hose (before the thing even got to any engineering team it was 'much too late to change the spec's because they already designed the wiring looms...For more same environments, usually overengineering a bit is enough to do the job. There still will usually remain down things that you just didn't think of or didn't think could reasonably be expected to happen (but Murphy's law is a b****).

author: Mecanix
author_rank: Frequent Contributor
timestamp: February 24, 2021, 01:08:29 pm
content: Thanks for sharing those views, p'chava. They are strangely similar to what my colleague here has, if not identical.Might indeed have to revert to conventional techniques, those promoted by our great 'standards associations', the 1970's style methods e.g. throw the unit in the wall and drop it until something fails and fix/patch that. Repeat step 1 until stuff stop failing lolAs said earlier in a side note its very difficult to work with IC and PCB manufacturers, practically impossible in fact. It is very difficult to gain access to the information about the materials they use in their production, most of them immediately shy upon request, other literally goes into ignore-mode. That being said all of what's left to the analysts are generic and averaged characteristics. Which equates to some 'throw in the wall until it breaks' science.On a promising note we have a model ready and a few test PCBs ordered from Europe (orthotropic characterized, miraculously) and plan on calibrating both the software and our solver using a 2.5W buck/boost IC (SO8-EP). A rosette strain gauge and 3 thermocouples are planned for real-life data acquisition and meant for comparison/calibration. Problem remains the IC manufacturer's unwillingness to help us out so that's on the WIP until we find a solution to that strange secrecy. Until then I'm truly curious as to how others accomplish these EE co-sims (we're soon to call it all BS).

author: jonpaul
author_rank: Super Contributor
timestamp: February 24, 2021, 06:13:28 pm
content: To: Mechanix ^^ Right, I see now, Jon :/ So you're saying failures are as dynamic and random as the weather in electronics, and trying to prevent the worst is lottery odds-like. Not exactly a good start!!!Nono, the statistics and math of reliability are NOT random, but well known.My examples were just my personal observations in the period 197-s...1990s.For best reliability the simple things are the best:Choose high quality parts that have reliability track record, from ISO 9003 suppliersDerate everything eg use a 35V 10 mF tant and NOT a 20V part on an 18V busUse a 20W resistor if the real load is 7W.Use a 105C electrolytic since 85C parts will have 50% out or C or ESR after 2000 hrs at 85 C.Mount heavy rats ruggedly eg transformers, inductors.Test at elevated temps and vibration at time/Gs excess of the worst caseUse worst case design in general.Far from random.So, aviation, military, nuclear and medical electronics designers pay a lot of attention to the reliability.Kind Regards,Jon