We have recently started a wave soldering line and the boards that we initially soldered were almost perfect.


After we stopped the line for a couple of days, on re-start and with no change to the initial setup, it looks like there is too much flux residue on the boards after soldering. If I reduce the amount of flux, then the soldering will be bad, bridges on the components etc. I use Asahi QF2062 no-clean flux, leaded solder (63%-37%), preheat 130-150-170C and solder temp 245C.


I appreciate your help as I am novice in the field of soldering

 

Is the flux applied inline? (spray fluxer,foam fluxer, dropjet fluxer??). Any changes in ambient conditions? (i.e. more humidity, higher temp,etc..) Does your wave solder machine have a nitrogen environment? Any changes in preheat time?
Is the flux tacky after soldering? Excessive dross build up?

 

^ The fluxer is spray and it is inline on a separate machine just before the wave machine. It has a few fixed nuzzles (in a line) which spray the flux to the PCB and the amount of flux can be tuned by changing the on-off time of the spray. I use 3ms on (spray) and 750ms off (not spray) and it used to work fine, but not anymore.

The ambient temperature is the same as before and there is no nitrogen environment. I tried different preheat temps but the result is the same.

The flux residue is tacky, it has some arc shapes (half circles) which appear mostly around the metal parts of the PCB.

The flux that I use is kept in a plastic container but the cap is not completely sealed. I initially thought maybe the flux has lost some solvent and it has become denser and that is why the flux residue remains on the board. Can it be the reason? But when I look at the flux level, the container is almost full so it has not lost significant amount of solvent (IPA?).

 

Your flux almost definitely lost solvent. You should pull a cup out of the bulk supply, and thin it. Apply the thinned flux to a test board and wave solder. Shut off the auto spray fluxer.

I think you will see a big change in the solder and cleanup quality.

Do a little test before thinning the whole batch. And REMEMBER to recap the flux SECURELY. It isn't water in there. That stuff evaporates so very quickly. 2 or 3 days is an eternity to flux.

Call the flux manufacturer (or read the label or MSDS) to find the solvent type and recommended thinning agent to use.

 

Solder,

I agree with retched. Do you have a flux titration kit? At a previous job, the line workers had to do flux titration and then they would determine if they needed to dilute or not based on the titration results. The flux we used was alcohol based, so they simply added 99.9% alcohol to dilute the flux. In your case, you would add whichever solvent is recommended by the flux manufacturer. After you check that, you may need to determine that the flux is reaching the proper temperature. The flux should have a temperature range in which it works properly. Just something to be aware of.

Make sure Quality/Engineering personell are involved when changing process temps. Changing temps could cause damage to components and or poor quality solder joints. I have seen improperly pre-heated and cooled pcbs develop cracked solder joints.

I would definitley contact the flux manufacturer and see if they could give you any pointers.

Best of luck,
C

 

Also, be sure to check the flux capacitor.



sorry..had to be done.

 

^ What is flux capacitor?

 

I guess you have never seen the movie 'Back to the Future'?

In that movie, the time machine used a part called the 'Flux Capacitor' to travel through time.

Sorry for confusing you. It was just a joke.

 

It's what makes time travel possible...

 

Also, be sure to check the flux capacitor.



sorry..had to be done.

"Wait a minute, Doc. Ah... Are you telling me that you built a time machine... out of a DeLorean? "

-Marty McFly

 

I tried measuring the gravity of my flux and it was exactly the same as the gravity of new flux. Any other suggestions about what can be wrong with my set-up?

 

1.Have you tried contacting the flux manufacturer to see if they have any pointers?

2.Have you verified that your pcb's are getting up to the correct temperature in order to correctly activate the flux?

3.What does the residue look like? Is it a clear? Is it colored?

4.Have you tried a different batch/lot of flux or a different flux?

5. Do you have the ablilty/tools to run a thermal profile?

A couple of things you might try.

-Try turning the flux down until it stops soldering well. Then turn it back up in small increments until soldering improves. This is to ensure that you aren't putting too much flux on the board. Instead of adjusting the spray time, you might try reducing the pressure as well.

-Ensure your pre-heaters are working correctly and the board is being heated to the proper temperature.

-You might try slowing down the wave solder transport to increase preheat time and wave contact time. *Note: you would likely have to adjust your flux spray on and off times if you did this*

-Ensure the your solder pot is not low on solder and is clean. If the solder pot is low your wave height will most likely be lower than it was previously.

-Ensure the wave height is satisfactory. Making sure you have good contact with the pcb.

I'm thinking the flux isn't being completely 'burned' off. Almost as if it's not getting hot enough. I may be wrong. It's hard to say. I have no experience with that particular brand of flux. Even though some fluxes claim to be 'no-clean', they still may leave a residue.

Regards,
c