Strange SMT reflow issue

[Psi]

Has anyone seen this before.
Basically the flux is trapping solder balls so they can't join up with the main group and it's leaving a mess of balls over the PCB after exiting reflow oven.

Solder paste is ChipQuik T4 no clean leaded solder and is applied with metal stencil. (Alignment on pads is perfect when it goes into the oven.
 
Reflow oven is just a dual element toaster oven on variac. In for 4min at 210C approx (from fluke dmm temp probe)
i don't think the oven is to blame, ive done boards fine before with the same setup.

Any ideas?
My thoughts are that A ChipQuik sucks and B ChipQuik sucks.

[IanJ]

Hi,

Good info here:-

Tiny Solder Balls After Reflow:-
http://www.circuitnet.com/experts/87416.html

Ian.

[wraper]

Expired or improperly stored solder paste. Generally solder paste is guaranteed to be good for 6 months if stored in refrigerator. Some solder pastes can become unusably bad if stored at room temperature for 1-2 months.

[Psi]

This paste was stored in the fridge since i got it from digikey.

[Psi]

Hi,

Good info here:-

Tiny Solder Balls After Reflow:-
http://www.circuitnet.com/experts/87416.html

Ian.

"You may have moisture in your solder paste which is causing the solder balls to explode off during reflow. This can happen if the paste is refrigerated and not allowed to get to room temperature before opening causing moisture to condense on the paste."

Thanks for that

That could be it, i grabbed the tub straight from the fridge.

[DTJ]

I don't use an oven, I use a heated plate & reflow with hot air so it may not apply to your situation.

I often get what's shown in your photo and applying more heat for longer generally fixes it.

[Kjelt]

Reflow oven is just a dual element toaster oven on variac. In for 4min at 210C approx (from fluke dmm temp probe)
Any ideas?

Yes have you ever heard of a reflow profile ? You are not following the profile specified by the manufacturer so anything can happen.
Esp placing a roomtemperature pcb directly in a 210C oven could cause splatter, secondly the phase where you get the flux to activate (120-160C) is absent so your flux might not behave as expected.
Finally since the normal reflow profile end temperature is around 230C you might also not get the expected result.

You do not follow the industry standard and then you start blaming the solder paste, really ? 

[Jeroen3]

If you get tiny solder balls it's because the flux boils, which is because you're heating too quickly.

[Psi]

If you get tiny solder balls it's because the flux boils, which is because you're heating too quickly.

Good point. Will try slower
Thanks

[Psi]

You do not follow the industry standard and then you start blaming the solder paste, really ? 

Yep. I am.
Because ive heard others say chipquik is terrible.
Also its worked fine before. Ive not changed my procedure. It just started happening and ive done 100s of board no problem in the past

[Kjelt]

Because ive heard others say chipquik is terrible.

why did you buy it then?

Also its worked fine before. Ive not changed my procedure. It just started happening and ive done 100s of board no problem in the past

You did the 100s boards with other paste and it just happened when you used the chipquick paste?
Then you know your answer, if you only change one parameter and the outcome changes it is the changed parameter which is the most probable cause.
Recheck with the paste you had before.

[tatus1969]

Hi,

Good info here:-

Tiny Solder Balls After Reflow:-
http://www.circuitnet.com/experts/87416.html

Ian.

"You may have moisture in your solder paste which is causing the solder balls to explode off during reflow. This can happen if the paste is refrigerated and not allowed to get to room temperature before opening causing moisture to condense on the paste."

Thanks for that

That could be it, i grabbed the tub straight from the fridge.

Did you stir it thoroughly and let it warm up to room temp before applying?

Another thing that I noticed: you have vias in the pad region, sucking away solder. That may exaggerate your problem.

[Psi]

Because ive heard others say chipquik is terrible.

why did you buy it then?

Also its worked fine before. Ive not changed my procedure. It just started happening and ive done 100s of board no problem in the past

You did the 100s boards with other paste and it just happened when you used the chipquick paste?
Then you know your answer, if you only change one parameter and the outcome changes it is the changed parameter which is the most probable cause.
Recheck with the paste you had before.

I bought it because there isn't much choice for no-clean leaded solder tubs from digikey.

na, ive been using this chipquik tub for a while. It's not that new, about half full.

Ive been playing around with the paste on PCBs using hot air at varying temps and speeds to see what causes it.
Seems i can kinda repeat the effect if i go too hot.
Not sure what this means yet. temp probe said oven was 210 which should be totally fine.

Hi,

Good info here:-

Tiny Solder Balls After Reflow:-
http://www.circuitnet.com/experts/87416.html

Ian.

"You may have moisture in your solder paste which is causing the solder balls to explode off during reflow. This can happen if the paste is refrigerated and not allowed to get to room temperature before opening causing moisture to condense on the paste."

Thanks for that

That could be it, i grabbed the tub straight from the fridge.

Did you stir it thoroughly and let it warm up to room temp before applying?

Another thing that I noticed: you have vias in the pad region, sucking away solder. That may exaggerate your problem.

No vias in pads, where are you seeing that?

Yeah, i let it get to room temp and also tried to pre-bake the pcbs at 80 for 15min to remove any moisture.
Same problem after reflow.

[Kjelt]

Ive been playing around with the paste on PCBs using hot air at varying temps and speeds to see what causes it.
Seems i can kinda repeat the effect if i go too hot.
Not sure what this means yet. temp probe said oven was 210 which should be totally fine.

Which temp you call too hot?
Try to place a tempsensor next to the paste to get a better indication of temp and time.
You can get temp sensors with usb connection for $60 the pc can record the profile which will give you better calibration of the experiments.

I suspect that your pre-heat soak time is too short or the soak temperature too high.