[sdiy] RoHS/Pb wetting/wicking (Was: Re: Boycott Mouser and ROHS)

[Seb Francis]

Ian Fritz wrote:
> At 05:32 PM 8/14/2006, mcb, inc. wrote:
>
>> Wanted to confirm an impression I'm getting.  I've done a few
>> RoHS-compliant board/component sets with Pb solder now.  I build
>> in an RF-style with flush or nearly flush solder-side leads,
>> no filets, and thorough wetting and wicking of solder into the
>> component lead holes.  It seems that the Pb/RoHS combination
>> doesn't wet quite as well.  Increased heat on the Pb solder seems
>> to improve things but it doesn't have quite the same wicking
>> action as Pb/Pb.  Is this my jingoistic imagination or is this real?
>
> It's real.  And if you look at the manufacturers' spec sheets you will 
> see they claim something like 90% wetability.
>
> Pre-tinning the component leads while gently rubbing the iron against 
> them seems to help.  Pain, though.
>

Slightly bigger drill holes in the PCB also helps the solder flow 
through easier.  I think also the type of PCB finish must make a 
difference, although I've only had experience with Immersion Silver 
finish which definitely doesn't wick the solder through the hole so 
readily.  I think it's fine though .. after all for SMT stuff all the 
thru-board connections are made by vias that have no solder in them at 
all.  And for SMT I have found Immersion Silver finish to be excellent - 
flatter than HASL so very easy to hand position components and with a 
good no-clean flux, wetting is not a problem.

Seb