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Wave soldering - black residue / bridging

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Wave soldering - black residue / bridging | 27 December, 2019


We are having problems with SMD wave soldering (ERSA)

used flux is BALVER ZINN 390-RX-HT

used solder is BALVER ZINN SN100C

preheat curve is 90sec to ~120deg C (according to application note of flux) speed of conveyer is 0.43 m/minute

this is video of glass passing thru

on the glass there is "ruler" for measuring width of contact area which is about 2cm bottom of the glass is on the same level as bottom of PCB panel

after passing thru solder wave there is a lot of black residue on glass(and also on tested PCBs)

1. is the flow of solder correct (solder falling/getting pushed to other side? tw) 2. what to do to avoid black/gray residue/dirt? 3. what to do to avoid bridging?

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Wave soldering - black residue / bridging | 27 December, 2019

I could not see pictures of your board - please attach one or two. So to answer your questions: 1. wave should not overflow over your board - mostly we use pallets as carriers to protect the assembly. 2. Solder dross is caused because your wave is not clean. You should clean dross daily and make a deep clean based bi-weekly or monthly...based on how often you run. 3. Bridging can be caused from multiple factors. Number one is flux. Pictures can tell us more.

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Wave soldering - black residue / bridging | 27 December, 2019

As has already been mentioned, black residue is usually either from dross or just a dirty pot, pump, baffles, etc..

I also saw that maaaany years ago in a system that used a flawed oil intermix "feature" but hopefully those systems are long gone.

Bridges can be caused by lots of things but component orientation, pot temperature, effectiveness of flux application (insufficient, uneven), preheat temp., wave height and conveyor speed are all possibilities. There is lots of troubleshooting information online. Just search "wave soldering troubleshooting" and see what pops up.

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Wave soldering - black residue / bridging | 27 December, 2019

In your video, it looks to me as though the bottom of the glass is too low, but, I can't tell for certain. As a general rule, keep the top of the wave no higher than the mid-point of the PCB. Top flow will take care of itself thanks to flux and capillary action.

The black bits are either dross, or burnt flux, or both. This is a no-clean flux that you are using, make sure that application of the flux and temperature/solder profiles in the data sheet are followed, to maximize evaporation of the flux. Personally, I hate using no-clean at wave solder.

To minimize dross, as mentioned, clean your pot regularly; skim dross before running boards through the machine, and consider using a dross reducer. To minimize burnt flux organics, consider the application of the flux, and temperature ramp shown in the flux data sheet. Also, consider using water-soluble flux, and washing the boards...this will eliminate any concerns about debris.

As for solder all depends on the cause of the bridge. Could be pin configuration, temperature profile, thermal loads on the board, flux application, etc. Until you identify root cause, it's tough to find the right solution.

cheers, ..rob

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Wave soldering - black residue / bridging | 27 December, 2019

thank you for reply

here is picture of the board

on the bottom are pins/components which height is about 3-4 mm from bottom of the board

we had to increase distance of board from nozzle to make clearance and we increased wave height because of it

on the top right is connector with pitch 2 mm ( minimum pitch TH component)

dirt is very hard to remove

1. wave does not overflow the board

2. we emptied whole bath and cleaned nozzle 4 days ago. we send solder for analysis and it had 0.2% Pb (last proces was not RoHS). Could this be a reason?

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Wave soldering - black residue / bridging | 27 December, 2019

Using no-clean flux will make the boards very difficult to clean. If you can switch to water soluble flux, your life will be much easier.

The "icicles" lead me to think that the board isn't getting hot enough in the pre-heat cycle, and/or there isn't enough flux coverage, and/or your travel speed across the wave is too slow. Given the appearance of the rest of the board, I would tend to think that it's getting enough flux.

The globbing of solder on the header (upper right in the picture) leads me to think that for that component, there's too much solder exposure/not enough peel-off...again, too slow through the wave.

How are you applying the flux? Hand spray, or through the flux sprayer on the machine? It looks like there is a lot of flux...maybe even too much, for the process to burn it all off correctly.

I would start by checking a thermal profile through preheat and wave, and making sure that it matches the recommendations on your flux data-sheet. If you're not hitting those temps/times, you won't burn the no-clean flux off correctly, and you'll never get a clean looking board.

You may also be able to get some process help from the flux/solder manufacturer.

I don't think that the low lead content would cause any of what you're seeing.

This is a pretty good troubleshooting guide to review, too:

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Wave soldering - black residue / bridging | 30 December, 2019

Thanks Rob,

this is excelent

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Wave soldering - black residue / bridging | 31 December, 2019

It looks like solder dross there or flux residue that not activated well. Your speed is 43cm/60s, wave width contact is 2cm, so dwell time is 2x43/60=1.43s, it's short also.

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Wave soldering - black residue / bridging | 31 December, 2019

The video showing wave contact is not consistent and not stable from width size, make it better.

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Wave soldering - black residue / bridging | 31 December, 2019

thanks again for reply,

we have now configured speed of traveling so pcb can travel through preheat with one speed (call it v1) and through wave with other speed (call it v2).

Lenght of preheat elements is fixed, so with speed v1 we can change preheat temperature profile

we are applying flux through Foamfluxer

also we wil try to play with contact area of board/glass with the wave

we will let you know results!

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Wave soldering - black residue / bridging | 18 January, 2020

We made much better contact of wave with board. There was not enough solder in bath. We increased it so wave height is higher with same pump power

And now board is pushing dirty wave to the other side and board is much cleaner!

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