Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Pad finish

Views: 3796

#62805

Pad finish | 30 September, 2010

Hi Folks,

I'm looking for detailed information about the different composition of circuit board pads.

We have been experiencing some issues with our solder, and I would like to know the differences between compositions. I do know that we ran a customer supplied PCB between our company products and the solder quality was nite and day different. The same paste was used for both.

Thanks

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#62807

Pad finish | 30 September, 2010

Were doing double sided, and I'm told our PCB finish is tin silver.

From a quick search I'm finding that for double sided assemblies we would be better off using ENIG.

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#62809

Pad finish | 30 September, 2010

Enig have been one of the industries leading finishes with great solderabilty and shelf life, And now Immersion Silver is starting to get popular.

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#62836

Pad finish | 4 October, 2010

I've done minimal research to this point and understand my issue with solder on the double sided boards is due to oxidation that occures on the unpopulated pads when the board makes its first trip through the reflow oven.

We did run both sides in a short time span, but the damage is still evident. I'm now looking to find a pad finish that is more tolerable for double sided reflow process.

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#62858

Pad finish | 6 October, 2010

> I've done minimal research to this point and > understand my issue with solder on the double > sided boards is due to oxidation that occures on > the unpopulated pads when the board makes its > first trip through the reflow oven. > > We did run > both sides in a short time span, but the damage > is still evident. I'm now looking to find a pad > finish that is more tolerable for double sided > reflow process.

ENIG is great for double sided reflow and long term storage. OSP is also good for double sided reflow.....most of the manufacturers of phones / hand held devices use OSP and all their pcbs are double sided reflow. OSP is not best for long term storage....process your pcbs within a few months and you should be okay. Avoid Immersion tin, the degradation of solderability on the second side always seems to be huge. HASL is also good for double sided reflow and storage, but you have to make sure your pcb supplier gives you pads with HASL on and not pads with tin/copper intermetallic on.

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rem

#62871

Pad finish | 7 October, 2010

I just swapped from the HASL to Immersion Silver mainly because the board house we use could not maintain consistency in keeping the pads level. I was constantly battling bumps and bad finishes on the pads. They are able to give me a consistent board using the Immersion Silver process.

I also was able to lower the temperature at reflow on every profile and still maintain very good solder joints. The only draw back to this process is the shelf life. After removing boards from their packaging they will tarnish after a few weeks, especially the top boards in the stack. I recommend planning your runs before breaking them out of the wrapper. They are a little more costly than HASL process. I would say plan on about 6% increase in the cost of a board.

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#62880

Pad finish | 7 October, 2010

Craig & Rem - I would also recomend switching to ENig - OSP would be my sencond choise

ENig will give you the flatness your looking for plus the best shelf life.

Enig is about 5% more than Hot Air. Enig also does not cause as much stress on the circuit board during its application as does Hot Air - With Lead free material - less stress is always better.

Regards,

Boardhouse

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