What Causes Solder Balls During Hand Soldering?

What Causes Solder Balls During Hand Soldering?
We have experienced solder balls during automated reflow. Now we are finding solder balls during the hand soldering. Phil Zarrow and Jim Hall, The Assembly Brothers, offer their own suggestions and recommendations for eliminating solder balls.
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
Phil Zarrow
With over 50 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.


Welcome to Board Talk with Jim Hall and Phil Zarrow of ITM Consulting, the assembly brothers. So what question is drifting our way today Jim?  

This comes from C.P. We have experienced solder balls during automated reflow and tweaked the process to eliminate them. Now we are finding solder balls during the hand soldering of some eight-lead SMT components.

Any idea what causes solder balls during hand soldering?  

Everything and anything just like what causes solder balls in reflow and wave. I guess the first question we would probably ask is what's different in terms of thermally or chemically.

The first thing Phil is to say are you using paste in doing your hand soldering which you used in reflow and found that adjusting the thermal profile eliminated solder balls or what I think is more likely is that you're using some sort of cored wire.

So the parameters are much different. Solder balls are typically caused by incomplete fluxing because the flux does not clean all the solder surfaces, becomes molten, the solder does not coalesce into one single mass and you get these little guys floating off on their own as balls with their own little oxide coating around them preventing them from coming back together.

So do you have adequate flux in your hand soldering operation and also I think as you indicated Phil, the thermal profile. Are your operators trained. Are they using the proper tip size and tip temperatures and IPC specified soldering techniques.

As Jim said, do you have the right tips? Do you have the right heat range for what you're doing? Have the irons been calibrated? That's another prerequisite.

And again how well trained are your operators? Are they soldering with the right end of the soldering iron?

I feel that my experience is that solder balls are not common in hand soldering.  One other thing that you would think of, if that was just a problem would be contamination of the leads of the parts that you're soldering.

But if they work in reflow with paste, I would think that that would not be the issue. But you can never be sure.

Whatever end of the soldering iron you're using, whatever you do don't solder like my brother.

And don't solder like my brother.


To many operators believe the old myth that flux is your friend and you can never have to much flux. That is not true as to much flux will outgas at the end of the hand soldering process creating solder balls around the connection. This is one possible explanation as others have stated other causes as well.
Frank Honyotski, STI Electronics Inc
Training has often told students to touch the wire solder to the iron as a way of speeding up solder flow. The solder contains flux. The flux vaporizes at iron temperature and causes the now liquid solder to explode. The result is a proliferation of (usually small) solder balls.
Jim Smith, Electronics Manufacturing Sciences, Inc.
In the case of cable assemblies, I have noticed them when using the very small heat shrinkable solder splices. Similar to the moisture comments, the heat shrinkable material will collapse around the solder ring in the center and seal off the heated gases from escaping. This is typically not an issue, until you start adding flux. In this case, more flux is not better. The additional flux will create a lot more pressure. When the pressure gets to great, the pressure will cause the hot gases to pop out around the weakest point of the solder slice around its wire seal. When the hot gases erupt out of the wire/solder sleeve seal, it will spew out solder balls with it.
Sky, Lockheed Martin
Hand soldering techniques with cored wire have been covered already. Squeezing the solder paste out by placing the component too deep in the paste causes the extra solder to ball up alongside of the chip. Simply lay the Part on top of the paste. You need a gap between the bottom side of the component and the PCB surface. Allow your Iron to do the work. With SMT Placement machines they critically need the correct component thickness and PCB thickness to ensure that placement of the component is not too deep schmooshing out the paste (and flux). Your nozzle gets just above the top of the solder paste and vacuum shouts off at the nozzle tip and a small puff of air leave the chip gently atop the paste pillow.
Dave Chapman, COILCRAFT
Personally, I've never seen solder balls with hand soldering. I could see how you'd see it if you're using paste, awful wire and not forgetting, perhaps inexperienced operator. Better get back to basics on this.
Dave Kearns, TinyCircuits
One question I'd like to ask: is it lead free solder that you're using? That would have an impact as well...
Peter Woodhouse, New Zealand
We are facing SMT components No solder and solder bridging issue (Glue PCBA) at wave soldering process. Fine tuned the wave parameters improved but not able to eliminate the issue. Suspecting because of moisture pad and component leads contaminated due this we are facing this issue.

After SMT Reflow process with in how many days wave soldering process to be completed for glue PCB'S & Normal PCB'S. or is their any other reason please suggest.
Shankar, India
Being trained extensively in High Reliability Soldering and Connections since 1976. I notice, when at my home hobby lab (dc-15 ghz capable) because it is quiet, I have long experienced the same issues using paste for rework/repairs. I also try not to use it(paste) opting for wire solder instead. One other item of interest is the amount of these balls is proportional to the loudness of "the sizzle" sound. I can agree some what with the moisture idea but just the flux itself "sizzling off" is also propelling balls in the area. Try this to see it yourself. get digital microscope cam, focus on little dab of paste, plunge in iron or hot air (hot air generates less due to more slow even heating) inspect area around dab and there they are>>>>
William Jones, Harimatec Inc.
Also, in agreement that most issues come from hand soldering techniques. I have found operators who do not keep the solder iron tip clean, will leave solder balls and splash around the solder joint, usually from the dross build-up on the iron. Feedback and refresher training help.
Bonnie Dewey, CIT, CQT, Saunders Electronics
Moisture is a contributor to solder balls. Trapped moisture, when ramped up to solder temperatures creates steam per se, pressure and out-gasses. Solder gets expelled from the solder joint, displaced, creating a ball. Keep in mind when using aqueous cleaning of PCBA's that they should be baked out prior to hand assembly or thru-hole. In the case presented here, its possible the 8 pin device they were hand soldering contained moisture. If the anomaly were specific to that part.
Tom McCarthy, TJM Electronics, USA
I agree that solder balls during the hand soldering process can often be attributed to hand soldering techniques. Use of a heat transfer bridge and a reduced feed rate of solder into the joint have helped me address this problem. Operators may try to improve their speed/efficiency by feeding too much solder into the joint too quickly. In a no clean process, when no external flux is applied, solder balls can result. IPC hand soldering training DVDs cover both topics and are a great training resource.
Anna Hill, Burton Industries, USA

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