shock & vibration testing - Page 1
Forum section: electronics / general

author: xaxaxa
author_rank: Regular Contributor
timestamp: August 27, 2018, 04:42:18 pm
content: I have a relatively simple product that is a single 10x10 cm PCB in a metal enclosure, and currently the quality control just consists of functional tests and visual inspection of the board. I have only sold less than 100 units but already saw 2 defects in the field. The units were all tested prior to shipping and arrived defective at the customer, so the damage is due to bad solder joints.Is shock & vibration testing every unit typically the solution or do most manufacturers rely on AOI/visual inspection? The PCBA manufacturer (elecrow) mentioned they are doing AOI, but that doesn't seem to have caught the failures.

author: ogden
author_rank: Super Contributor
timestamp: August 27, 2018, 05:11:39 pm
content: Quote from: xaxaxa on August 27, 2018, 04:42:18 pmPlease be specific. - Bad reflow, wave or hand-soldering joints? Please tell more about those 2 defects. What you mean by saying "units were all tested prior to shipping"?QuoteManufacturers usually rely on 1) PCB houses with AOI capabilities 2) thermal cycling (environmental) chambers and/or 3) burn-in. Vibration tests are not common unless you manufacture specific product for harsh environment. For usual electronics you do vibration tests only on prototypes and maybe first batch to reveal mechanical/PCB_layout/packaging engineering errors.In short: consider thermal chamber. Cycle count and time proportional to product priceUsually you cycle through whole specified temperature range at least two cycles, each cycle ~1 hour or so. If have spare time - run as many cycles as your manufacturing specifics allows. Obviously equipment shall be running continuous full (self-)diagnostics during thermal cycles, reporting/logging any errors

author: xaxaxa
author_rank: Regular Contributor
timestamp: August 27, 2018, 05:32:40 pm
content: Quote from: ogden on August 27, 2018, 05:11:39 pmOne report of a capacitor falling off into the enclosure, and another functional failure that is still pending diagnosis. The testing before shipping are functional tests and RF characteristics tests. The board is all surface mount and is reflow soldered.I'll look into thermal cycling tests.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 27, 2018, 11:32:15 pm
content: It doesn't have to be bad soldering. The casing, board or board mounting could be subject to or causing mechanical stresses.

author: coppercone2
author_rank: Super Contributor
timestamp: September 02, 2018, 03:20:09 pm
content: You might find something obvious with testing a single board, you don't need to commit to full vibration testing if you can't afford it. Plenty of places don't.Obviously unless your volumes are insane looking at PCB's under a magnifier is not really expensive or time consuming compared to environmental testing or vibration testing. Adding full thermal test capabilities on your assembly line means people and a definite bottle neck in your factory (this falls under a burn in test which is no fun for manufacturing). Means you need alot of space to handle any kind of volume and some technicians because they need to fill out reports about every board for the process to have any sort of meaning (so you can track quality and also track the board during that phase because it might be mishandled or such, its an additional process step), and you need to calibrate and maintain all those fucking machines. Also often leads to shipping delays. Since its a bottle neck you will need alot of storage that you might not normally need. Calibrating an oven right is a pain in the ass, you need to check for uniformity, and then you need to calirbate your temperature sensor.If you don't invest in massive parallelism you might end up with things like having to shut down your production while tests are conducted, meaning you need shift management and stuff, or cross training of employees. Then you end up paying people to do nothing, or figure out how to titrate the testing so that everyone is at full capacity all the time so you are not wasting money on people and machines sitting around doing nothing, occupying space and ruining moral. You need a skilled manager to maintain this feedback loop since it will change based on demand and production volume.Then if you commit to it in ISO procedures, and a testing machine breaks down, you got a clog in your factory, since you can't really ship the board unless you lie. Quality is expensive.No idea how vibration testing looks like. I assume its a even bigger PITA then thermal because there are moving parts and its more expensive then some ovens. I figure you need at least 2 hard working people to maintain 1000/year testing. You can't have people running around between tasks all the time because they lose focus and probably make mistakes and its annoying as hell to break your work flow every few hours to switch a board or something.And you need database management software at this point too when your manufacturing gets this complicated . This is another irritant because if the database fails your running at reduced efficiency.Then there is the psychological of knowing "i spent this much money on a goddamn test lab and its not finding any problems".. can be hard to acceptAlso if a oven fails and starts overheating your boards or something, settings are misconfigured, etc, you can end up sabotaging yourself, which means even more vigilance is required. Kind of like if you do programming in house with a marginal programmer. The last thing you wanna find out is that some giant shipment was baked to 150C for 4 hours by accident. Means you need good technicians that notice stuff, not scared to report mistakes.

author: Mr. Scram
author_rank: Super Contributor
timestamp: September 02, 2018, 08:55:45 pm
content: I think vibration testing a few representative samples during development can be a sensible step. Depending on the guarantees you want to give, leaving it at that can be acceptable. It depends on whether you want to find flaws in your design or in your individual products.

author: ogden
author_rank: Super Contributor
timestamp: September 03, 2018, 07:01:37 am
content: Quote from: coppercone2 on September 02, 2018, 03:20:09 pmUnless you cook your stuff in gigantic wood oven by gorillas, it won't happen. Modern environmental/temperature chambers have all the necessary control and protection against runaways.Here's chambers and vibrators as well:http://thermotron.com/.

author: coppercone2
author_rank: Super Contributor
timestamp: September 03, 2018, 05:29:30 pm
content: Quote from: ogden on September 03, 2018, 07:01:37 amI was giving an extreme case. But if you say in your ISO you test at 70C with some tolerance, and its accidentally set to something higher say after a calibration or something and you fail to notice, you are already in a shady place. Customer might think I never ever want that thing to go above 70 again. I will keep it in a lab with 0.05 degree temperature stability. I only bought it because you did not write 80c. It can easily be considered an accelerated ware test, and you wanna sell the least worn thing possible (to some people, other people want it tortured to hell).I don't know about legality, but I would expect ethically for a manufacturer to tell me if they deviated from their ISO practices (say you form an opinion (and additional test data) about the product based on something you bought before, or learned about it from a partner).But of course if your honest someone might say 'i don't want that batch anymore, make me another one', then you are up shit creek if you did some kind of special engineering feature for them, or there is no other demand for that product.. so you need to store it and try to sell it to someone else.And there is every bushiness reason in the world to hire gorillas and run a wood oven. You are supposed to conjure money out of thin air. Even better if you steal because then you technically have more and everyone has less.

author: ogden
author_rank: Super Contributor
timestamp: September 03, 2018, 07:59:30 pm
content: Quote from: coppercone2 on September 03, 2018, 05:29:30 pmTelling that thermal chambers are scary stuff and you can trash your production in them just because someone can set wrong temperature is... weird, to say it politely. You accidentally can set reflow oven temperatures higher as well.

author: coppercone2
author_rank: Super Contributor
timestamp: September 03, 2018, 08:01:44 pm
content: Quote from: ogden on September 03, 2018, 07:59:30 pmyup you can.

author: ogden
author_rank: Super Contributor
timestamp: September 03, 2018, 09:08:37 pm
content: AgreedIndustrial thermal chambers usually are (shall be) automated. Gorillas that are placing stuff in the oven shall not have any chance to change temperature profile.Baking/cooling at extremes does indeed reveal some/many temperature-related problems, but most important test happens during temperature changes. Then solder defects are revealed or weak solder links crack during factory test, not in the customer premises.Engineers shall definitely cycle their prototype board runs through thermal chamber -at least to check that choice of capacitor type/capacity is ok