Solder Joint Discolouration

#81685

Solder Joint Discolouration | 4 January, 2019

Hi,

We are observing solder joint discoloration ( yellow color appearance ) in one of assembly after secondary reflow run. Please provide your valuable feedback.

Solder paste : water soluble lead free Alloy : SAC305 Flux : ORM1.

Please provide valuable feedback. Image attached.

Regards, Ameen

Attachments:

Solder joint Yellow color.jpg

#81686

Solder Joint Discolouration | 4 January, 2019

Try to measure the profile again by datasheet..with the result that you will reduce the temperature in the areas below...increase the upper temperatures as needed according to the properly measured profile...I hope you can solve the problem like this...sorry for bad eng. All the best

#81687

Solder Joint Discolouration | 4 January, 2019

Hi,

Thanks for the valuable feedback.

We are at lower spec :

( TAL )Reflow time : Around 50 Sec ( Above 217 deg C) Peak Temp : 240- 245 deg C.

Any other suspects.

And your English is fine :)

Regards, Ameen

#81688

Solder Joint Discolouration | 4 January, 2019

If I understood on that electronics, you have a bot and a top side...and problem is when is first side in oven second time...So I thought that the temperature in the lower part was lowering..and increase in the upper temperature part in your oven. then re-measure the profile...If necessary, increase the temperature from the top or lower the temperature in the lower zone...

we had the same problems with one electronic that we resolved like this

#81689

Solder Joint Discolouration | 4 January, 2019

Hi ,

thanks..

yes you are right.Its bot and top side.

Decreasing the lower heaters and increasing the top heaters for secondary side.

will this matter in convection reflow ovens. Since the heat at the end will get equally distributed.

We were suspecting it to be something related to cleaning.Since we never had this issue.with the profiles we were using from long time.

will consider bottom heater point.Will definitely try.

You had a issue with water soluble paste friend.?

Regards, Ameen

#81691

Solder Joint Discolouration | 4 January, 2019

we never used a paste of this type...not everything in the paste type and profile..Everything has an impact on soldering quality and sensitivity of materials quality and type of pcb...atmosphere and nitrogen in oven...Try step by step to solve the problem...Are you doing a monthly test profile?You mentioned something about cleaning?

Every month when we are doing line maintenance we are doing a test profile...everytime after maintenace that test profile must be ok and same like the rest of the past months...

#81693

Solder Joint Discolouration | 4 January, 2019

Hi,

Here we take profile for every changeover. And we compare it with our profile.For the oven performance.

We daily take a minimum of 3 profile for one oven. We have High mix low volume production.

We are using ORH1 ( organic flux with halid content ).

We once had a cleaning issue of the flux, which in turn corroded the board. At customer end.

Lab report of PCBA showed there was chlorine content , which was not cleaned properly.

So now also we were analyzing our cleaning efficiency.

Regards, Ameen

Steve Thomas

#81699

Solder Joint Discolouration | 7 January, 2019

Hi,

I would like to try to help, but I think I need help in understanding your problem better.

1) do you see any discoloration of solder joints on the first side, after first side reflow?

2) after second side reflow, are solder joints on just the first side discolored, or is it on both sides?

3) You've stated that this is limited to just one assembly, correct? If so, did you purchase the pcb's from a trusted supplier, a new supplier, or are the boards purchased by a customer from an unknown supplier?

Thanks,

Steve

#81705

Solder Joint Discolouration | 8 January, 2019

Hi Steve,

We did the below trials today.

1. Run the board in O2 environment.

result : Yellowish appearance was observed.

After DI water Cleaning : Still the yellow color is there.

2. Same board run secondary side.

Result : First side board yellow color appears more.

After DI cleaning : Yellow appearance was there in first side.

Second side was ok.

3. The boards were run in N2 environment.

Result : very minute discoloration .

After DI water cleaning : Its acceptable.

Conclusion : With N2 environment. The boards had very minute yellow appearance, which is accepted.

And after cleaning it was ok.

Regards, Ameen

Steve Thomas

#81720

Solder Joint Discolouration | 9 January, 2019

Sounds like you're making progress!

The one thing that you might still want to investigate is the cleanliness and surface finish quality (and chemistry) of the pcb you're building with.

You haven't said whether this board was purchased through your own trusted suppliers, or a consigned part from a customer, but it's possible that you could be dealing with some chemical contamination of the pcb from the factory.

That has happened to us before with a consigned board, and the customer just accepted the product as-is.

#81728

Solder Joint Discolouration | 10 January, 2019

Hi Steve,

Thanks.

This from the trusted supplier.

HASL finished PCB. Even PCB supplier is using the water wash flux for fabrication.

Its almost eliminated with N2 environment.

And we had got a expert view from Dr. Lee of Indium on the issue stated as below.

"Pls see below statement from Dr.Lee and I had couple of discussion with him; he mentioned, in air reflow we can expect slight oxidation of flux ingredients and metals/alloys; it will be good to run in N2 to reduce this phenomenon.

As the assembly passed the ionic contamination test it is believed the yellow patches are not causing any reliability issue. "

"The flux Indium3.2 does contain chloride. But, it was not the cause of yellowish appearance. The yellow color mainly caused by flux got oxidized. The yellow color is mainly a cosmetic appearance, and is not related to corrosion or reliability"

Regards, Ameen

SMTA-Timothy

#81779

Solder Joint Discolouration | 18 January, 2019

It's unlikely to be a reliability issue. It looks like tin oxide. Nothing to be too concerned about. Otherwise your process controls sound robust.

This message was posted via the Electronics Forum @ SMTA SMTA

#81780

Solder Joint Discolouration | 18 January, 2019

Hi,

Thanks for the valuable feedback.

Thanks ALL.

Regards, Ameen

davef

#81784

Solder Joint Discolouration | 19 January, 2019

cColor is NOT a measure of solder connection quality. It is a process indicator. So, you're being smart by trying to figure out whats causing he discoloration

#81785

Solder Joint Discolouration | 19 January, 2019

Thanks Dave,

For the feedback. It was initially rejected by our customer end. so we had to submit complete analysis report with lab test of the PCBA.

#81786

Solder Joint Discolouration | 19 January, 2019

Have you tried to reduce the temperature for the second side of pcb?Try to reduce it to the minimum below the regulations by datasheet...

#81787

Solder Joint Discolouration | 19 January, 2019

Hi,

Thanks .

It was ok with N2 environment.

Reducing below recommended temperature of the supplier. It was not ok for us.. We had BGA components. Which were getting affected if we reduce temperature below recommendation.

Regards, Ameen

SMTA-Tony

#81790

Solder Joint Discolouration | 21 January, 2019

Lead free HASL coatings can be susceptible to yellowing during reflow due to oxidation of the tin in the coating. Some HASL solder suppliers use anti-oxidant additives in the solder to limit or prevent yellowing of the coating. You may want to ask your board supplier about the HASL solder alloy and see if they can use a solder alloy that includes anti-oxidants.

This message was posted via the Electronics Forum @ SMTA SMTA

#81791

Solder Joint Discolouration | 21 January, 2019

Hi Tony,

Thanks for the valuable feedback.

We got to know about the flux they use ( they were using organic water soluble flux) .

Alloy we didn't enquire. Will try to do that.

thanks.,

Regards, Ameen