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Blowholes during wave soldering

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#51574

Blowholes during wave soldering | 28 August, 2007

I have problems with blowholes during the wave soldering process. I already find out that the stock time between reflow and wave is the most important. The longer the boards are in stock the more blowholes we have.

We don't have a climat controlled stock for the reflowed pcb.

There are 2 options now for eliminating this problem:
1. maximum stock time
2. Buy a climat controlled system for the stock

Question: Does anybody know what is the maximum stock time between reflow and wave. The boards are sealed with silicagel before reflow. The humidity is about 40% and the temperature about 20 degrees celsius. We use FR4 goldplated.

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#51575

Blowholes during wave soldering | 28 August, 2007

If the copper on your PTH is not one thou, you will get blowholes. With the cost of copper going through the ceiling, you will get less than one thou of copper plating from substandard suppliers.

Consider baking your boards prior to wave soldering as an alternative.

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#51586

Blowholes during wave soldering | 28 August, 2007

Lead-free? White-tin finish?

Even if it's not, it sounds like a moisture/contamination issue.

If your boards must sit in stock between reflow/wave, consider giving them an alcohol bath to clean up any contamination, and a good baking to remove any built up moisture.

Unless your process can be redesigned to eliminate the stock period between reflow and wave...

cheers
..rob

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#51589

Blowholes during wave soldering | 28 August, 2007

thats goofy

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#51590

Blowholes during wave soldering | 28 August, 2007

Blows holes are usually caused by improper amount of flux applied to the boards prior to WAVE process and, in some circumstances, can be related to the preheater settings.

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#51593

Blowholes during wave soldering | 29 August, 2007

It is a lead free process with sac305. We use goldfinish FR4 boards. Preheat is between 110 and 115 degrees.

I am sure it is a moisture problem because longer stored boards have more blowholes.

What is the maxium period to store the boards without having problems with blowholes?

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#51633

Blowholes during wave soldering | 3 September, 2007

hi,

This is moisture problem, I think.I have similar problem.You must try to bake PCBs.I bake our PCBs in solder wave mashine , under solder pot.There T is about 80*C - after 6-8h the PCB is dry

regards

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#51634

Blowholes during wave soldering | 3 September, 2007

Joris

We don�t know the maximum period to store the boards without having problems with blowholes. Too many variables to determine. We prefer to just fix the problem, but understand that you have stock that you need to build-down.

Determining moisture content:
* Use a very accurate balance (X.XXX) with enough range to weigh your board. Handling residues (such as hand oils) can influence weight measurements. The transfer/dwell time for the weight measurement can affect your readings.
* Our ol� friend Bob Willis gives us a nondestructive test for outgassing in bare boards here: http://www.trafalgar2.com/troubleshooter/wave_pin_blow_hole.htm

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#51688

Blowholes during wave soldering | 6 September, 2007

are you sure it isnt down to an hygroscopic contaminant causing the problem.I've only ever seen it once or twice in gold,really quite unusual.Its not too much gold brightner or similar residue.If it can be cleaned off then it shouldnt be there so it maybe a brightner salt attracting moisture.Try not to bake as it will encourage the nickel to migrate into the gold causing poor capillary.
hope it helps.

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#51689

Blowholes during wave soldering | 6 September, 2007

Hi Joris - There is an excellent wave solder guide called "Take No Prisoners" that includes instructions for attacking and eliminating solder balls and preventing their recurrence:
1. Increase Dwell Time
Solder balls are normally caused by too much flux solvent still on the board when it hits the solder wave, causing
tiny explosions as the solvent vaporizes when it comes in contact with solder. One cure can be to increase
your dwell time, to give your wave more time to reliquefy the solder balls. Go to http://www.WaveSoldering.com/ WSO/DwellTime.htm for background on the importance of your dwell time. Dwell time is the time each lead is in your wave, not the amount of time a board is in the wave. And remember, your dwell time is directly determined
not only by your conveyor speed, but also by your immersion depth, contact length and wave shape. Have you identified the best dwell time for each board type that you assemble, and do you verify optimal dwell times every shift?
2. Increase Preheat Temperature
Another approach is to increase preheat temperature to ensure that your flux�s solvent is removed in the preheaters, leaving only the flux�s solids to be removed by the solder wave. Be careful not to provoke too high a
maximum preheat slope, as this can induce thermal shock to your components even before your board reaches the solder wave. Also, too high a preheat temperature can burn away flux solids as well. This can cause insufficients.
Remember, preheat temperature is taken one centimeter before your solder wave; maximum preheat slope is the maximum increase in board temperature in any single second interval prior to reaching the solder wave. Your preheat temperature, maximum preheat slope, maximum temperature and delta T should be verified every shift simultaneous to measurement of your fluxer performance and board-wave interaction.
3. Porous Solder Mask
Solder balls are also caused by a porous solder mask. Solder will sometimes adhere to exposed copper, giving
the appearance of a solder ball. You can determine the quality of the solder mask in relation to IPC standards
by using a microscope. This is a materials problem for which you must contact your circuit board vendor.

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#51701

Blowholes during wave soldering | 9 September, 2007

Wave Optimizer-person

Help us understand how your "excellent wave solder guide called 'Take No Prisoners' that includes instructions for attacking and eliminating solder balls and preventing their recurrence" will help Joris resolve his / her issues "with blowholes during the wave soldering process."

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RDR

#51717

Blowholes during wave soldering | 10 September, 2007

Aren't the solder balls a result of the blowholes? you know the solder that came from the blowholes is now the solderballs on the resist!

hahaha :-)

Russ

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#51720

Blowholes during wave soldering | 10 September, 2007

Hi Dave - You are correct that I was not clear in my comments. I assumed Joris had seen the usual solder balls accompanying his blowholes.
Nevertheless, Joris, my first two recommendations still stand. Increasing the dwell time of your leads in the wave may cure your blowholes very quickly, simply and thoroughly. And, adjusting your preheat, keeping in mind all of the caveats, may also help. You have understandably focused on stock time because that is the variable most evident. These suggested wave solder process adjustments might relieve you of the need to worry so much about the logistical cures like adjusting stock time. Put differently, it's possible you'll find it much easier to try these process adjustments before you worry about instituting new stock time specifications. If they work - and it shouldn't take more than an hour to adjust and test your process - your in great shape. Easy investment, big payoff. If they don't work, you're back to stock time.

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#51725

Blowholes during wave soldering | 10 September, 2007

See there Mr. Smartbutt, you were correct in spite of your more cynical tendancies. B)

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#51748

Blowholes during wave soldering | 11 September, 2007

KRIKIES! If that wasn't a sales pitch, I don't know whut was, me lad.

Optimizer is good for DoE's and process characterization, but no substitute for the artform that is wave soldering. When me lads here in Purchasing get PCB's from all over the world, with different finishes, different board houses, different solder masks, different lots, varying levels of solderability, etc... that, me friend, is where the artform and innate knowledge of wave will come in. Knowing the science and the artform, me lad, is where it's at - so I am told.

Whut do I know, chap. I am merely but a Q.E. now.

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#51749

Blowholes during wave soldering | 11 September, 2007

Hi Shrek - Not sure why you think adjusting dwell time and preheats is a sales pitch, but I do appreciate your candor. These are proven, widely used techniques for attacking, eliminating and preventing the recurrence of blowholes. Since it is so easy and quick to see if different dwell times and temperature windows can reduce blowholes, why not do this first before changing other manufacturing systems? And, if a more optimal dwell time or temeprature window is identified, it can be measured subsequently to ensure it is maintained each time the the board type in question is run.
Of course, there are different steps one would take for other types of wave solder defects, such as bridges or insufficients.
About your comments on wave soldering as an artform, no doubt you are an experienced and very good quality engineer, so that your instincts lead you to control the wave solder process. Yet behind what you have termed an artform is both knowledge and measurable, quantifiable data. This can be captured and responded to methodically, thus demystifying the wave solder process.
Such an approach is certainly critical to those engineers and process managers less experienced than yourself, but is also useful to those, like you, who can quickly take advantage of it because of their strong background.
There are specific, step-by-step procedures for identifying the optimal wave solder process parameters when new boards come into a plant, optimal being the measurable parameters for that specific board type that generate the fewest, if any, defects. It's possible that your expertise makes such procedures less vital to you, but in my experience most facilities, when first introduced to them, embrace them as new and vital based on the results they see.

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#51909

Blowholes during wave soldering | 27 September, 2007

Thanks for all the answers.

Is it also possible with lead free soldering to produce little holes in the solder that are not blowholes?

We see holes where you can see the end of the hole (not very deep). The holes are always on the same places.

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#51910

Blowholes during wave soldering | 27 September, 2007

Joris,

Yep, very common to have those small blow holes in lead-free alloys. We used to get them very consistently on white-tin finished boards, and less frequently with gold finished boards, for what ever that is worth.

IPC-610 actually allows them as an anomaly in section 5.2.2, albeit as process indicators for class 2 and 3.

cheers
..rob

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#51911

Blowholes during wave soldering | 27 September, 2007

> Joris,
>
> Yep, very common to have those small
> blow holes in lead-free alloys. We used to get
> them very consistently on white-tin finished
> boards, and less frequently with gold finished
> boards, for what ever that is worth.
>
> IPC-610
> actually allows them as an anomaly in section
> 5.2.2, albeit as process indicators for class 2
> and 3.
>
> cheers ..rob

Not over here in the UK they are not common unless there is a board problem.
cheers
greg york

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