Tact Switch corrosion after soldering - Page 1
Forum section: electronics / general

author: Emanuel
author_rank: Regular Contributor
timestamp: February 20, 2020, 08:27:39 pm
content: I am experiencing a weird phenomena.I received for repair several devices we assembled about one year ago.We found that the some tact switches are detached from the board or fall if little force is applied.It seems that the pins start some form of black corrosion that expands also in the soldered area.The switches are from a reputable manufacturer, C&K and the reflow process was OK, no other parts on the board have any issues.What will be a logical explanation?By the way, one disturbing thing is that as large as C&K are, it is very difficult to get in touch with the QA dept. or anyone to check and give an answer.In the attached photo the soldering looks good, with proper wetting but the black corrosion is clear, if compared to a brand new switch in the lower right corner.

author: thm_w
author_rank: Super Contributor
timestamp: February 20, 2020, 10:56:01 pm
content: Is that rust in the second photo, top right behind the tantalum? Or is it just a reflection.I have seen this black corrosion on some through hole switches before, they were kept with a bunch of other parts and no others had problems. So to me it was a manufacturing issue and not environmental.There is some mention of it here, not sure if its the same thing:https://books.google.ca/books?id=YWMGCwAAQBAJ&pg=PA103&lpg=PA103&dq=ic+lead+black+corrosion&source=bl&ots

author: ANTALIFE
author_rank: Frequent Contributor
timestamp: February 21, 2020, 12:47:23 am
content: Those look like C&K KSC7's to me, if so they have a MSL rating of 1 (unlimited). So would not think incorrect storage prior to assembly is the culprit, especially if board was assembled with a pick & place machineYou say you got them from a reputable manufacturer, but who was your supplier & PCB assembler?

author: Shock
author_rank: Super Contributor
timestamp: February 21, 2020, 02:07:51 am
content: Looks like plastic off gassing if it's only on those switches.

author: Cerebus
author_rank: Super Contributor
timestamp: February 21, 2020, 02:55:55 am
content: You haven't mentioned the exact switch part so I can't look it up but what is the plating on the switch contacts?The reason I ask is that looks just like the kind of tarnish you'd get on silver (Ag) plating if there is any sulphur about - even in the form of small quantities of volatile sulphur compounds e.g. SO2, SO3, H2S, or even organic compounds like mercaptans (thiols) or the various sulphur compounds associated with faeces/decay. Have they been in use near any burning process that releases sulphur compounds (oil or coal burning)?

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 07:58:32 am
content: Quote from: thm_w on February 20, 2020, 10:56:01 pmThere is no rust anywhere on the board, all the parts are in perfect condition.

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 08:05:10 am
content: Quote from: Cerebus on February 21, 2020, 02:55:55 amIt is a C&K switch KSC741JLFS.In fact these boards were assembled in a product - not water tight but closed.And for sure were not used or stored near any known sulphur sources.

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 08:06:14 am
content: Quote from: Shock on February 21, 2020, 02:07:51 amBut this can happen only if heated, or not?

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 08:17:13 am
content: Quote from: ANTALIFE on February 21, 2020, 12:47:23 amThey are indeed C&K KSC741JLFS, purchased from DigiKey or Mouser and assembled by a p&p machine, therefore the packing was in a tape.I tried to check what MSL they have, but the data sheet won't mention it anywhere.The assembly was made by us, we have our own assembly line.

author: Shock
author_rank: Super Contributor
timestamp: February 21, 2020, 10:12:04 am
content: Quote from: Emanuel on February 21, 2020, 08:06:14 amCould be a reaction to a cleaning solvent, the button or oils or any number of things. Try to narrow it down to time or a batch.

author: fcb
author_rank: Super Contributor
timestamp: February 21, 2020, 10:20:24 am
content: Have you checked your reflow profile. Make sure you aren't overcooking them.

author: Cerebus
author_rank: Super Contributor
timestamp: February 21, 2020, 11:44:25 am
content: Quote from: Emanuel on February 21, 2020, 08:05:10 amAnd the data sheet says "contact material - silver" and leads silver plated.It could be oxide rather than sulphide (oxide tarnish is pure black, sulphide tarnish has a brownish tinge) but I've never seen silver tarnish that heavily from mere room temperature oxidation without some other chemical process going on to help it along. To be clear, normal atmospheric levels of SO2etcetera are enough to mildly tarnish silver, but nothing like the level you're seeing.Something to consider would be flux residues. Are you using a flux that promotes corrosion/tarnishing in silver? Look for something that might be catalytic/promoting as well as compounds that are outright corrosive as far as silver is concerned. You might have to talk to your flux supplier and ask if it's compatible with silver.Your other alternative would be to switch to the gold plated version of that switch - KSC743JLFG - however that looks to be a special order part rather than a stock item.

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 12:36:39 pm
content: I think there is a problem with these switches.We are using them in a product that is exempted from lead free and use a KOKI SS48-M955 solder paste with a 2% Silver content.The reflow process is for sure not overcooking them, the rest of the board looks perfect including parts that are more sensitive.The switches are stored in a tape as supplied and assembled by machine.But here is what I just found.I examined some switches that were rejected by the machine and we kept them in a plastic bag.They all look to be well oxidated. So I took some from the tape and they look the same.

author: Psi
author_rank: Super Contributor
timestamp: February 21, 2020, 12:48:09 pm
content: My thought are that it's either- Really old stock- A bad batch from manufacture (metal mix is wrong or contaminated)- Fake parts (substituted by someone unknown to you)

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 01:04:02 pm
content: Quote from: Psi on February 21, 2020, 12:48:09 pmThe MSL mentions no special storage limitations, and they were stored in the original tape. something I will need to check.The thing is that we received several products for repair made in different batches, with switches purchased from both Mouser and DigiKey.On top of all, we assembled a new batch and because of the parts sent for repair with this problem we checked the new batch and they look like in the photos.So the old stock possibility is not valid, unless was sold by DigiKey or Mouser with an old date code, same thing about a bad batch from the manufacturer.Fake parts from Mouser and DigiKey..... well, I really hope they are not down to that level, but who knows.For sure nobody substituted them here and again we are talking about several batches purchased since 2016.Regarding the reel in use, I will look at the manufacturing date.There is one thing that bothers me, there is no address at C&K to send this complaint and expect an explanation.

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 01:15:29 pm
content: Quote from: Cerebus on February 21, 2020, 11:44:25 amWell, as shown in the second photo they were in a plastic bag in the production area, not outside and this is the result.Same about some that I took out of the tape.This answers also to the flux residues possibility.The gold plated version seems like something that exists only in the catalog.Among other things I am worried about is that now I only see a soldering problem - which is a serious problem if I will need to recall several thousands products from all over the world.The question is, if the oxidation expanded outside between the solder and the leg, perhaps it expands also inside the switch.I was just reading that silver oxidation is conductive, but who knows what can happen inside the switch.

author: Cerebus
author_rank: Super Contributor
timestamp: February 21, 2020, 01:48:44 pm
content: Quote from: Emanuel on February 21, 2020, 12:36:39 pmYup, exactly what I'd expect silver plated contacts to look like after a few weeks/months of storage. Those will solder fine, the flux will strip that oxide off in a moment. You've specified a part with silver plating, it is behaving like a part with silver plating, there is no manufacturing fault. If you chase C&K down their response will be the same.Edited to add: Just because silver is used for jewellery does not mean that it is a noble metal to the same degree as other jewellery metals such as gold or platinum. Silver jewellery needs cleaning, ask your mother/sister/auntie/grandmother. Silver gets used in electronics because it is highly conductive and its oxide is also highly conductive relative to other metal oxides.

author: free_electron
author_rank: Super Contributor
timestamp: February 21, 2020, 01:56:15 pm
content: These pins are pure silver plated. You may be using the wrong solder alloy ...

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 02:00:13 pm
content: Quote from: Cerebus on February 21, 2020, 01:48:44 pmYou think that black oxide is stripped by the flux? Then what is causing the switches to fall from the board?Even if little force is applied from the sides the switch dislocates.The reflow profile was tested, all other joints on board look perfect.The part was specified by pressure force and actuator length, I wish they were making the gold plated version, but they don't

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 02:02:21 pm
content: Quote from: free_electron on February 21, 2020, 01:56:15 pmI am using KOKI SS48-M955 solder paste with a 2% Silver content

author: free_electron
author_rank: Super Contributor
timestamp: February 21, 2020, 03:38:04 pm
content: Quote from: Emanuel on February 21, 2020, 02:02:21 pmThat doesn't mean anything. It may not be the right alloy for this component. just because it has silver in it doesn't mean anything.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 21, 2020, 03:54:28 pm
content: Have you tried hand soldering some of the corroded switches, to see if the flux and solder you use takes to them?

author: Emanuel
author_rank: Regular Contributor
timestamp: February 21, 2020, 07:18:19 pm
content: Quote from: free_electron on February 21, 2020, 03:38:04 pmIt will be quite a task to use different alloys for different components.The products we make are exempted from lead free regulations.This solder paste was recommended as a compromise when soldering lead free components to a tin plated PCB with SnPb(Ag) alloy.The other option is sending the components for replating.I used the specific switch type for more than 20 years, before the RoHS era, and the silver coating is unchanged.So practically I don't think the alloy is the problem. The 2% silver was added for other reasons, not to make it more compatible with silver plated components.As it does a great job with all the other parts, including LED and modules I think it will be easier to find another tact switch perhaps with gold plating and better technical support.

author: tooki
author_rank: Super Contributor
timestamp: February 22, 2020, 05:52:30 pm
content: If they're falling off the board and it's not the solder joints cracking, then they never properly soldered to begin with. My hunch is that the flux isn't aggressive enough and simply isn't getting through the oxide layer. Or the reflow profile isn't right, such that those joints aren't getting hot enough long enough to properly activate the flux.How well are the switches holding on right after soldering? (I suspect they've been weak from the beginning.)Have you tried hand-soldering some of these to see how they behave? What about with added flux?Quote from: Emanuel on February 21, 2020, 08:06:14 amNo, off-gassing happens at any temperature, though heat promotes it. New car smell? Off-gassing. The smell of PVC when you unpack a new shower curtain or inflatable flamingo for the pool? Off-gassing.That said, silver tarnishes readily, so even without a specific incident, they could oxidize. But if it's just one batch, then probably something happened during storage.

author: Cerebus
author_rank: Super Contributor
timestamp: February 22, 2020, 06:58:31 pm
content: Quote from: tooki on February 22, 2020, 05:52:30 pmWell, now we know howyouspend your weekends.

author: tooki
author_rank: Super Contributor
timestamp: February 22, 2020, 07:00:14 pm
content: Sadly, I don't have a pool to use inflatable flamingos with!

author: SilverSolder
author_rank: Super Contributor
timestamp: February 22, 2020, 09:24:34 pm
content: Quote from: tooki on February 22, 2020, 05:52:30 pmAgree. It's worth a manual test with a soldering iron to see how this stuff behaves.

author: Psi
author_rank: Super Contributor
timestamp: February 23, 2020, 12:12:08 pm
content: Maybe it is outgassing related, as suggested previously.What exactly pushes down on the tact switch? Is there a unique rubber/plastic piece that contacts the switch?Due to its close proximity to the switch it might be causing the pins to oxides much faster than everywhere else ,

author: tooki
author_rank: Super Contributor
timestamp: February 23, 2020, 12:53:18 pm
content: Quote from: Psi on February 23, 2020, 12:12:08 pmIt’s almost 100% certain the oxidation happenedbeforesoldering.

author: Emanuel
author_rank: Regular Contributor
timestamp: February 24, 2020, 07:36:02 am
content: I tried some hand soldering, it goes well and it seems the black oxidation won't interfere.

author: tooki
author_rank: Super Contributor
timestamp: February 24, 2020, 11:01:06 am
content: Then something with your reflow process isn't right. Either the flux is not aggressive enough, or the reflow profile isn't right.

author: Emanuel
author_rank: Regular Contributor
timestamp: February 27, 2020, 08:18:09 am
content: Well, after a full investigation I couldn't find more switches so I will isolate the problem to a single board with a bad soldering.This is regarding products assembled long time ago.But I found that there is a problem with the last batch made a few days ago, when I posted the question.All the parts except for the 2 switches on this board were soldered perfectly.The switches, most of them, will drop from the board if pushed a little from the side by hand.The reflow profile was checked and soldering by hand looks ok, although a little more difficult than expected, probably because of the black oxide.Other parts with larger mass and pads have perfect joints.The only thing I found is that the machine operator used recovered solder paste.I know that this is a separate subject to discuss, but it looks that there was a problem with recovered paste.

author: SMTech
author_rank: Frequent Contributor
timestamp: February 27, 2020, 10:26:46 am
content: Well how solved you should call that depends on exactly what they mean by "recovered paste, paste has a shelf life and a life once open for the tub, where a special paste is used for one product there can clearly be a temptation to break those rules, you really really shouldn't.However given these switches do clearly have an oxidization issue and its clearly something that pushes the limits of what this flux can handle I would suggest at the very least you look at choosing a paste chemistry with a specifically aggressive flux. However I would also check the profile genuinely gives the flux enough time at the right temp to do its job, on this actual board in that location not some generic test PCB. The 2% silver paste does seem to be a a genuine recommendation but it would be so much less hassle to just use a better more reliable tinning in the first place and luckily for you there's a world full of switches out there and most of them are pretty generic.

author: Emanuel
author_rank: Regular Contributor
timestamp: February 27, 2020, 07:20:08 pm
content: SMTechI totally agree with you.The operator never used recovered paste alone, he is starting always with new paste and only if the level requires addition he uses recovered.There are a lot of disputes about using or not recovered paste, some say that mixing 1:1 is OK, others are against.There are disputes about everything, even about mixing by hand or machine.The thing is that this time he used recovered from the beginning, big mistake.You mentioned the board tinning, as we use leaded alloy we also order the boards with leaded finish or gold (ENIG)

author: wraper
author_rank: Unknown
timestamp: February 27, 2020, 07:33:21 pm
content: IMHO usage of recovered paste depends on what paste is used. If it's something like GC10 which is room temperature stable and has "Printing: up to 72 hours stencil life, Printing: up to 24 hours abandon time" I don't see why not to reuse it. It's not like it dies when removed from stencil. On the other hand some pastes are short lived. Also some pastes tend to separate liquid and solid contents with each print, so paste becomes dryer (contains less flux) over use.

author: SMTech
author_rank: Frequent Contributor
timestamp: February 27, 2020, 09:13:59 pm
content: I use a paste from BLT similar to GC10 (or even better) and I certainly reuse it, but its a special long life paste that can handle being treated that way. Once put on a stencil, that paste goes into a new tub and fresher paste is used with that paste, primarily so that if the used paste is contaminated, its not affecting the whole tub.Your Koki paste has pretty decent decent tack time but makes no claims for the kind of abuse "recoverd" might imply, recovered how often, mixed with what, how long since the pot was opened, how was it stored, how long did it spend on the stencil..

author: Emanuel
author_rank: Regular Contributor
timestamp: February 28, 2020, 12:07:13 pm
content: I know that in the past we used recovered paste with no problems.Of course, always put in a separate jar.But this time something went wrong, very wrong.Here is the result on tests made on blank boards.Looks like poor wetting, almost no pad was covered completely while on some a small ball was formed which drops off and leaves the pad unchanged.We opened a new jar and repeated the test, everything was perfect, so it wasn't a reflow or board problem

author: SilverSolder
author_rank: Super Contributor
timestamp: February 28, 2020, 01:40:27 pm
content: Nice test/verification/QA work there. Assumptions are always what gets us...

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 28, 2020, 01:49:40 pm
content: Quote from: SilverSolder on February 28, 2020, 01:40:27 pmIn this context, it's your name that gets me

author: Emanuel
author_rank: Regular Contributor
timestamp: February 28, 2020, 02:29:47 pm
content: Well, as I am getting obsessed by this thing, I made another test.Looking at the poor wetting of the pads I had another assumption. Not enough flux remains in the recovered paste.So I mixed a new jar and the recovered jar with the mixer at the same parameters.I took some 20g samples of each and melted with hot air.Washed the flux and compared the weight before and after melting, without the flux.The sample from the new jar went perfectly, the flux accumulated on top, looks like very clear honey.After cleaning it gave exactly 90% of the paste weight, as mentioned in the data sheet, 10% flux.Unfortunately I was expecting something else with the recovered paste so I made no pictures.Now I did the same with the recovered paste and...... look what I got.Between the melted solder and the flux some contamination or god knows what it is.For sure not liquid, weights less than the solder/lead and more than the flux, as it stays between them. Also not melting at 300-400°CI assume some metal or oxidation?If so where it comes from?The final result was 13% less weight, but it is impossible to determine what is what.It is more than 10% flux, but can be moisture and the weight of this contamination. So I am not sure if the flux was still 10% or less.The idea was to add flux if the result was more clear. I got from KOKI the exact flux used in this alloy.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 28, 2020, 06:53:57 pm
content: Quote from: Ice-Tea on February 28, 2020, 01:49:40 pmLOL yeah, I was kind of compelled to comment on this thread!

author: SilverSolder
author_rank: Super Contributor
timestamp: February 28, 2020, 07:00:31 pm
content: Quote from: Emanuel on February 28, 2020, 02:29:47 pmWow yes that looks pretty "dirty". - is there a way of filtering it before use? Or perhaps give up on trying to recycle flux if there is anything even remotely challenging about the job...

author: Emanuel
author_rank: Regular Contributor
timestamp: February 28, 2020, 07:28:41 pm
content: Of course, this paste will not be used, there is no way to filter it.The idea was to make a small test and see if the problem with recovered paste is the flux percentage, maybe due to evaporation.If it was so, it could be easy to determine the present percentage with such a test and add flux of the same type.But the test showed something unexpected.This worries me even more, as I have no clue where the contamination came from.What if it is from something in the process and I start a batch with new paste that in time is contaminated?The FAI will show perfect and after 100 boards the disaster will strike.One thought is if the squeegees blades are scratching the stencil and what I see are small particles from it.I am using moderate pressure, 4-5 kg for 300mm blades and none of the stencils made more than 3000 boards.

author: wraper
author_rank: Unknown
timestamp: February 28, 2020, 09:43:00 pm
content: It's not contamination. It's simply oxidized solder alloy which did not reflow.

author: Emanuel
author_rank: Regular Contributor
timestamp: February 29, 2020, 08:16:33 am
content: Quote from: wraper on February 28, 2020, 09:43:00 pmAnd this can be the reason for the poor wetting as in the pictures above?

author: Cerebus
author_rank: Super Contributor
timestamp: February 29, 2020, 02:19:54 pm
content: Quote from: Emanuel on February 29, 2020, 08:16:33 amYeah, because if you've got excessive levels of oxides in the solder itself as well as on the surfaces to be joined it's going to 'use up' the reducing power of the the flux (once it's activated) to remove the surface oxides that prevent wetting.

author: free_electron
author_rank: Super Contributor
timestamp: March 03, 2020, 01:09:15 pm
content: if that paste is exposed to air all kinds of things can happen. first of all : what is the flux type ? water soluble ? that stuff pulls humidity out of the air and saponifies.-the flux becomes much less reactive.-the solder corrodes ( or oxidizes or whatever chemical name you wanna give it )-water soluble flux that is not removed will eat certain platings over time , and is conductive. i have had circuits fail due to the flux remnants become 100k to 220k between two adjacent pins of a tqfp. ( 0.5mm pitch)

author: Emanuel
author_rank: Regular Contributor
timestamp: March 03, 2020, 02:23:41 pm
content: Quote from: free_electron on March 03, 2020, 01:09:15 pmIt is No-CleanKOKI SS48-M955

author: Cerebus
author_rank: Super Contributor
timestamp: March 03, 2020, 02:38:52 pm
content: Quote from: free_electron on March 03, 2020, 01:09:15 pmChuckle. I find it faintly amusing that someone who calls themself 'free_electron' is apparently uncomfortable with the chemistry of oxidation - which any chemist will think of in terms of the movement of free (valence) electrons from one ion to another and has little or nothing to do with oxygenper se.

author: Emanuel
author_rank: Regular Contributor
timestamp: March 03, 2020, 02:50:10 pm
content: After some further investigation it seems that not only the operator used recovered paste, he used to put it in the refrigerator.And this was repeated many times, as the recovered paste jar is full.No wonder I found this oxidation, but his question is, how other boards were soldered perfectly with the same paste?Although not in the same batch, not the same boards, but still, how was this possible? The QC found no problems with boards from earlier batches.

author: SilverSolder
author_rank: Super Contributor
timestamp: March 03, 2020, 03:08:38 pm
content: Quote from: Emanuel on March 03, 2020, 02:50:10 pmPerhaps if the board and parts were already very clean, even a "weak" paste might be enough? Whereas if there actually is a challenge (tarnished silver) it can't cut it...

author: Emanuel
author_rank: Regular Contributor
timestamp: March 06, 2020, 01:18:02 pm
content: Not sure if will be better to open a new topic, I will continue here.Apparently the problem was solder paste oxidation, almost for sure because it was stored in the refrigerator.It is well know that once a jar is opened it should not be put back in the fridge as there is a risk of moisture accumulation.It is also known that below 10°C and unopened it can be stored for 6 months, after opening and outside but not more than 30°C it will last 1 month only.We have a situation then, as we have assembly runs 2-3 times a week and not big quantities.If recovered paste is risky to use and new jar will last for only 30 days after opening we are sending back to the supplier about 70-80% of the paste purchased.Simple physics explains that practically inside a closed fridge there is very little moisture after a couple of days, but once the door is opened condensation is immediately accumulated.Some claim that if the paste jar at room temperature is placed in the fridge it accumulates moisture.I am not sure about this, but I am sure that when taken out from low temperature to room temperature immediate condensation is created, kind of a thermal shock.Suppose we make some device like a can refrigerator used in cars, with peltier cooler, add a smart controller and do the transitions from room temp. to say 5-7°C and vice versa at a slow and controlled rate.Will this solve the problem?

author: wraper
author_rank: Unknown
timestamp: March 06, 2020, 02:06:20 pm
content: Quote from: Emanuel on March 06, 2020, 01:18:02 pmYou can put it in a fridge many times. But you should not open the jar when taken out of fridge until it reaches room temperature.

author: wraper
author_rank: Unknown
timestamp: March 06, 2020, 02:14:37 pm
content: QuoteDepends on solder paste. 1 month out of fridge and especially at temperature as high as 30oC is way too much for many pastes to be considered still up to standard. Some are good for something like one week. 10°C storage temperature is also too high for some pastes.

author: Emanuel
author_rank: Regular Contributor
timestamp: March 06, 2020, 02:26:02 pm
content: Quote from: wraper on March 06, 2020, 02:14:37 pmThese are the specifcations for KOKI paste I am using.But this is not the point, the warning is against storing an opened jar in the refrigerator.And speaking about when taking it out from there for the first time, not to open it immediately.So my question is about avoiding all this with a device that controls in fact the temperature ramp.This way an opened jar can be kept at low temperature and used for longer periods.If my theory is correct of course.

author: Emanuel
author_rank: Regular Contributor
timestamp: March 06, 2020, 02:26:50 pm
content: Quote from: wraper on March 06, 2020, 02:14:37 pmBut this is totally against the manufacturer's instructions

author: wraper
author_rank: Unknown
timestamp: March 06, 2020, 03:28:20 pm
content: Quote from: Emanuel on March 06, 2020, 02:26:50 pmParticular paste should be stored <10oC. That's truefor this particular paste. But I don't see any claim it being good for 1 month @ 30oC.

author: Emanuel
author_rank: Regular Contributor
timestamp: March 06, 2020, 03:42:01 pm
content: Take a look on the last page