0603 Resistor often found broken in half..why? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: December 09, 2023, 06:08:52 pm
content: We have a PCB....its an 60W offline led driver....it has a 100k 0603 resistor on it. Only a few milliwatts dissipation.In every 100 boards going through production, one of these 100k resistors will be cracked in half......you cant ever even see the crack....you only know its in half when you touch one pad with hot iron, and the cracked half tombstomes up. It often measures 100k even if cracked, since the crack is held together.I reckon its due to the boards being rough handled, and a mechanical shock wave goes on in the board, and centres on that very resistor , resulting in the crack...but others think its got unevenly heated pads when in the smd solder bath......and that cracks it...what do you think is the problem?.....its not a "bad resistor batch" problem as different batches have the same problem.

author: coppercone2
author_rank: Super Contributor
timestamp: December 09, 2023, 06:09:48 pm
content: cuz its like driving a grave stone down the street instead of a monster truck

author: Faringdon
author_rank: Super Contributor
timestamp: December 09, 2023, 06:17:48 pm
content: Thanks, its a real mystery...and bad news, if 0603 resistors can get cracked with such ease.....mechanical resonation in the board when dropped/banged about.....handled roughly

author: coppercone2
author_rank: Super Contributor
timestamp: December 09, 2023, 07:10:48 pm
content: IDK the resistor is robust the capacitor is IMO the one that breaks.It means you need at least 4 screws, a rigid chassis element, etcits not a mystery that a microscopic ceramic structure breaks easily. Its just that people demand density in equipment. Then you have cost, and some notion that for some reason not having a wire is some how modern and more advanced............................ I would like to keep my suspension system thank you very muchthese x2y capacitors I was playing with are ridiculously fragile at 0805 IMO.the old 'old pickup truck is easier' thing mechanics say its 100% trueto me its kinda like needing train tracks instead of cheap asphalt or concrete road not built to runway standards. then you can get by with a few springs and dampers instead of being taxed to death for road maintenance. I think crysler developed the car suspension in 1930. you can even drive down a dirt road with it !the smt part reminds me of a flintstones car or a steam rollernotice the typical characteristic of SMT parts in the lower right hand side of the picture. the SMT version is similar in resilience as the flintmobile to a battlemech

author: floobydust
author_rank: Super Contributor
timestamp: December 09, 2023, 09:13:08 pm
content: OP also check that the resistor is not getting hit by something - PCB trays, carts, pick'n'place, reflow etc. during assembly, handling, as well as the bed-of-nails during test.It might simply be in a bad spot, heavy component nearby causes PCB flexing.I had one vendor hitting and cracking resistors when they plugged in their IDC connector for loading firmware. It was their fingers/screwdriver scraping them when pulling off the connector. So the vendor went ballistic complaining it was a quality problem blah blah. I had pics of the board before being sent out, the parts were there and fine. That settled it.I like that video, a chart recorder using smokeinstead of ink and shock absorbers part of the chassis in 1938 - not the disposable strut trash we have nowadays that does not last.

author: Gyro
author_rank: Super Contributor
timestamp: December 10, 2023, 10:30:14 am
content: Photo of the board, with the resistor locations highlighted?

author: jmelson
author_rank: Super Contributor
timestamp: December 10, 2023, 04:48:02 pm
content: A particular board I have made about 300 of used 0603 resistors exclusively. It was about 100 mm square. I NEVER had a single cracked resistor on them. So, I strongly suspect rough handling, possibly having many stacked boards without some kind of soft material between them.Jon

author: nali
author_rank: Frequent Contributor
timestamp: December 10, 2023, 05:22:46 pm
content: Quote from: Faringdon on December 09, 2023, 06:08:52 pmEasy. Next batch you inspect and retouch that resistor with an iron which will tell you if they failed during manufacture.(SMD solder bath? Do you mean reflow line, or do the boards get wave soldered for THT parts on a 2nd run or something like that?)

author: bostonman
author_rank: Super Contributor
timestamp: December 11, 2023, 03:57:20 am
content: Is the resistor orientated in the direction of the PCB in the long way or the short way? Maybe the PCB is flexing at a specific point and stressing the resistor.Maybe re orientating the resistor will help; but pictures would help.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 11, 2023, 07:15:55 am
content: Post a photograph. It tells more than a thousands words.

author: coppercone2
author_rank: Super Contributor
timestamp: December 11, 2023, 08:23:10 am
content: this is what i mean there is like 5 people talking about how to zone some rando resistor and this would just not happen with a TH part! talk about annoying overhead and booby traps.damn the complicated zoning beurocracy of SMT parts.I wonder what will happen in a impedance analyzer if I take some resistors I have and measure them before and after smashing the lead into a ribbon using a press.also, if you bend the lead, a resistor aint gonna get off the board even if the via has a total bond failure, because its anchored by a bent wire.

author: mikerj
author_rank: Super Contributor
timestamp: December 11, 2023, 11:18:46 am
content: Quote from: coppercone2 on December 11, 2023, 08:23:10 amThe component density wouldn't be achievable with TH parts either. Life is full of compromises.OP, check for anything that could be stressing the PCB in the area of the resistor e.g. a connector that requires some force to connect/disconnect, a test jig that applies pressure near this point etc...

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 11, 2023, 01:22:50 pm
content: Almost fell in.Really? You have 20+ years knowledge in electronics field and you answer this?Is it near the side? It's the PCB depanelizer almost for sure.Otherwise, you have someone who previosuly worked dumping cement bags, and uses the same delicate process for the PCBs.If it was the pcb flexing during the reflow process, probably other parts would break too.

author: wraper
author_rank: Unknown
timestamp: December 11, 2023, 01:31:42 pm
content: It depends not only on PCB handling but also on component placement and amount of solder (more solder -> easier to crack). For example you don't want fragile SMT components placed near to a V-cut, especially in perpendicular orientation. Also you don't want them anywhere close to mounting holes.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 11, 2023, 01:51:37 pm
content: At least you're investigating it.We're having lots of issues with a large 1mm thick pcb, lots of QFNs are coming badly soldered, mostly lacking solder, sometimes you have completely clean golden ENIG pads.Again this is not my job, but it annoys me inmensely that everyone is giving zero foocks to it.My theory is that someone is screwing it up with the stencil, taking away the solder by lifting the stencil too fast, or either because with colder temps the paste thickens up.Guess what, the good ones flew away to other company and they put there some peasants that only knew about football.Those will call you freak or nerd because you're into electronics.Talked to some managers, shrug their shoulders "Better to not try anything, we could screw it further".Gotta fly out of there!

author: SMTech
author_rank: Frequent Contributor
timestamp: December 11, 2023, 03:26:08 pm
content: Quote from: DavidAlfa on December 11, 2023, 01:51:37 pmThere's is little point in inventing theories if you have no eyes on the process. Paste can stay in the stencil because the stencil is not clean, because the stencil has incorrect area to thickness ratio for that aperture, using old paste, using the wrong paste. Snap off could be invalid (gap between stencil and PCB), separation wonky/too fast/slow, they could be manually printing a board that is beyond their skill level to do that way and should be using a machine. However, you have a 1mm thick PCB, printing requires good board support and at 1mm thick it gets more important as those are very bendy, that could push some of the blame back into your court, if you have specified/supplied a panel that is very difficult to keep fully supported because its full of routing and very sew nibbles it would only take a beancounter somewhere to refuse to pay for dedicated tooling and you would problems just like this.It could even have a manually created paste layer generated from the gerbers rather than in the CAD at design time and they've missed pads(or randomly added some for THT parts can happen too). However if you are outsourcing overseas and getting something that bad, take it elsewhere.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 11, 2023, 04:06:01 pm
content: We have our own smd/smt production line, only the PCBs are outsourced, but as I say I know nothing about it, but I know the people working there and they're the closest thing to rednecks which were given nice cloths.Yep, just classy rednecks who came one year earlier from studying electronics (Not a degree, and absolutely not related with smt processes), barely knowing how a DMM works.The directives's thinking is "It has always worked like this", meaning no need of I+D of any kind, it'll just work because it always did.Some kind of electronics survival with Bear Grills, you're alone in this, adapt, overcome.I tried reworking a tssop using the flux they use for BGAs, it was the dirtiest thing I've ever seen, a drop in the pins and the solder tip became totally black, leaving a crude residue in the pcb.BTW we had a lot of issues with BGAs that month... Go figure why, I won't judge too soon, but I hated that flux lol.Being ignorant about that flux (Maybe normal behavior because it's meant for BGAs, not for iron rework, right?) still trying to be constructive I asked the reason of using it, and if they ever tried Amtech stuff, as I used it for 7 years non-stop in repairing all kind of electronics with amazing results.Am...what? Huh... -insert some excuse here-.The paste they use is bad as f***, leaves the pins blackened (I thought it was the part itself but nope), barely flows, it always looks like cold joints (But I know rohs is rarely pretty), and indeed we have plenty of issues with "floating" pins, which look soldered but they're not.

author: thm_w
author_rank: Super Contributor
timestamp: December 12, 2023, 12:58:09 am
content: To me it looks like the QFN is sitting too high up. It should be 50-75um at most.So maybe an issue with the paste or reflow curve.Blaming production and calling them names with no evidence of wrongdoing is a bit lame.

author: floobydust
author_rank: Super Contributor
timestamp: December 12, 2023, 01:05:03 am
content: I can see white silkscreen extending underneath the IC, on the left. That lifts it up.Check the footprint, it looks suspect.

author: DavidAlfa
author_rank: Super Contributor
timestamp: December 12, 2023, 06:30:13 am
content: Regardless the height, it's lacking a lot of solder, that same board comes with a lot thicker joints when ok.That was a "good" one, as I said lots came in plain enig finish, sometimes the entire IC is held by 2 pads, no paste at all.It's not that they're making errors, we're all human after all, it's the fact they simply pass.Lots of these were already fixed by hand by a guy after exiting the ovens, what I find are the ones he missed.He was pretty pissed off, apparently he had to rework not less than 5-8 QFNs in each board.