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Solder beads and wave soldering

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#42536

Solder beads and wave soldering | 3 July, 2006

Hi,

I am experience problems while testing wave soldering SMT components that are glued on the solderside (lead free).

Between de leads of SOx type IC's and SOT's develop a great deal of solder beads.

I have been using a RSS temp.profile while sprayfluxing with MF300S flux. The sprayfluxer has been setup to deposit a minimal amount of flux to prevent splattering on the wave.

The only thing that improved the developing of solder beads has been applying twice the amount of flux. This caused splattering on the wave and a sticky residue.

Since many pcb's are supplied by our customers it will not be easy to change f.i. board layouts, component orientation and solder resist.

Any of you ideas or experience on this matter?

TIA

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RDR

#42555

Solder beads and wave soldering | 5 July, 2006

Sounds like possibly too little preheat.

Russ

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#42556

Solder beads and wave soldering | 5 July, 2006

Is the flux rated for lead free? These higher temps will cause most lead rated fluxes to burn off prior to the wave.

Jerry

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Chris Griffin

#42565

Solder beads and wave soldering | 5 July, 2006

Likely causes of this are:

-Preheat temp. too low -too much dross -uncured epoxy -PCB contamination

...also varify the solder flow over the wave is smooth.

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ronalds

#42574

Solder beads and wave soldering | 6 July, 2006

Thank you all for your input.

The MF300S Multicore flux is rated for lead free. There is not much dross or contamination. We are using nitrogen. I've tested the boards with the curing test of IPC-TM-650.

I think you're all right about the preheat. Maybe there's insufficient drying for the wave.

More preheat however will take me beyond the limits of the values from the fluxdatasheet.

I am now considering using a different head for the sprayfluxer, wich will spray less flux, but more efficient.

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Rob

#42577

Solder beads and wave soldering | 6 July, 2006

MF300S is quite an old flux, & a lot has happened since then on the flow solder front - are you sure it's designed for Lead free, or is it just a traditional flux that SHOULD work OK with Lead free?

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Chunks

#42582

Solder beads and wave soldering | 6 July, 2006

Sounds like your flux to me. Since you cannot change the board or the machine, changing flux would be one question mark you could take away with a phone call and a sample. You will really be surprised how different fluxes can affect your final product.

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#42584

Solder beads and wave soldering | 6 July, 2006

..and he can put the flux in and keep it a secret too from his customer..

RSS profile on wave?? I never heard of a soak zone for wave preheat...you may be burning off your activator..hence, the beads. For wave preheat, your main goal is to ramp up your board and components and activate flux.... you don't need a fancy profile...

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ronalds

#42621

Solder beads and wave soldering | 10 July, 2006

You are right, RSS profile is not the correct description.

I am using a profile which heats up quickly to let the flux spread. Next linear up to activate the flux and prevent thermoshock.

My experience is however, that small changes in this profile do make a big difference in the results.

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#42628

Solder beads and wave soldering | 10 July, 2006

Here is a nugget from the Data Sheet...

Wave Soldering: Excess moisture on the PCB during soldering may lead to random solder balling and poor wetting of some solder joints. IT IS IMPORTANT that the flux solvent carrier (water) is fully evaporated and that the PCB appears virtually dry when it reaches the solder wave.

(Link: http://tds.loctite.com/tds5/docs/MF300S-EN.PDF )

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