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Electronics => PCB/EDA/CAD => Topic started by: mwilliams03 on January 22, 2018, 05:51:51 am

Title: QFN and QFP, what service to use ? HASL or ENIG
Post by: mwilliams03 on January 22, 2018, 05:51:51 am

I am using fine pitch QFN and QFP components and i have read that it is better to use immersion gold finish instead of HASL... why is this so?
In my prototyping, I have never had any issue hand soldering the components to a HASL PCB.

Title: Re: QFN and QFP, what service to use ? HASL or ENIG
Post by: AndyC_772 on January 22, 2018, 08:35:22 am

HASL isn't guaranteed to be flat, so with a component like a QFN, there's a chance that it'll sit at an angle to the PCB, and the pads along one or two edges won't solder when the board is reflowed.

Gold, silver or OSP finishes are perfectly flat, so coplanarity isn't a problem.

If you're hand soldering, then you should be OK either way. Personally I prefer gold finish for hand soldered PCBs because, if nothing else, the difference in colour makes it obvious which joints have been soldered and which haven't.

Title: Re: QFN and QFP, what service to use ? HASL or ENIG
Post by: jpanhalt on January 22, 2018, 10:50:22 am

The immersion finishes are flat.  However, note that immersion silver was found to have its own problems with creeping corrosion: https://www.dfrsolutions.com/hubfs/DfR_Solutions_Website/Resources-Archived/Publications/2005-2007/2007_08_creep_corrosion_on_lead-free_pcb_in_high_sulfur_environments.pdf (https://www.dfrsolutions.com/hubfs/DfR_Solutions_Website/Resources-Archived/Publications/2005-2007/2007_08_creep_corrosion_on_lead-free_pcb_in_high_sulfur_environments.pdf)  Immersion gold is apparently less susceptible.

Of course, for a short-lived prototype that shouldn't make a difference.