Electronics > Beginners

Hot air soldering - balls

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JonPyro:
Hi All,

I have done my first hot air soldering this afternoon after ordering a pro board and stencil from JLC. I am using chipquick solder paste (lead free, you cannot buy leaded within the EU as retail anymore).

I warmed the board up for about 20 seconds at 100 degrees (lowest my hot air gun can go) and the board was about 30mm away using fairly large nozzle, about 9mm nozzle. Then upped to 160 degrees to fully melt with air speed about 80%.

From a visual inspection it looked quite good, until i looked with an eye glass. Between my pads are loads of very tiny solder balls, all hanging out on the solder mask. I have tried to get a photo but I don't have a microscope of macro lens so I tried to shoot through my magnifier, you can see the edge of the pad lined with balls but this continues across with ever smaller balls.







Could anyone suggest how to stop this from happening?

I have tried spending more time a lower temperature and the opposite, high temperature and soldering as quickly as possible - these didin't work. I have also tried to replicate the oven profile of the paste with limited success and that doesn't seem to help either. could this be too much airflow? not enough airflow?

My solder paste was warm as i had left it out the fridge for about 5 hours.

GreyWoolfe:
That very well might be due to the high air pressure you used.  I was soldering a few 0605 and 0402 passives and I had my Quick 957DW turned down to between 1 and 2.  Very little air movement was necessary.  I started out higher but started to blow components a little.

worsthorse:
Based on the splatter and the look of the solder joints, too much air pressure combined with too much movement. Check the size of the nozzle attachment, turn down the blower, don't try to do too large an area at once. Think about how a simple reflow oven works... no air movement at all, just heat. 

JonPyro:
Ok so I tried turning down the air speed to 10% And raises the temperature slowly over about 4 mins inline with the datasheet for the paste making allowances for loss of temperature.

However, my result still has solder balls lining the pads :(

TheHolyHorse:
I'm no expert so I could be far off here but isn't 160 degrees way to low. Like it wouldn't even melt leaded solder.

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