[Diy_efi] info

[Bevan Weiss]

>> Oh brother.  Ok,  I'll agree that some other people using some other
>> materials and some other circuits have had problems with water.  This
>> particular conformally coated PCB , however, should have no problems with a
>> water rinse and dry.
>>     
>
> Ok sure, no problem - agree for the most part 'should' being the
> operative adjective subject to a degree of long term uncertainty ;)
>
> Rgds
>
> Mike
How bout we settle it and just use what the integrated circuit industry 
uses.

Pre-production all washes utilize de-ionised water, followed by a warm 
oven dry period.

Post/Inter-production:
The first wash is performed using acetone, as this is the best solvent 
for removing skin oils, as well as heavier greases etc that may drift 
onto the surface from moving machinery.
Second wash is with methylated spirits, because this leaves less residue 
on the surface than does acetone.
Third wash is with isopropyl alcohol, this has the best  residue 
removal, and so leaves the surface very clean and practically oil/dust free.
The final wash is with a purified nitrogen blast, this further aids in 
removing (via evaporation) any remaining solvent on the surface, as well 
as assisting with the forced removal of large residue.

Now if we're being sensible, we won't do all these steps, quite likely 
because several of the solvents will ruin conformal coating and/or 
solder-mask, and also because it's just not needed.  Sure deionized 
water may not be the best option in all situations, but if ya got it at 
hand, and don't have any IPA then why not use it?

I know that's what I'd do... especially if the board was initially 
covered in anti-freeze, I'd just wash it all away with deionized water.  
And that's exactly the recommended solution.  You should never mix two 
chemicals unless you know what will occur on their interaction.  I'm 
sure you'll just say that anti-freeze is ethylene glycol and water, 
however can you be sure without actually reading what the anti-freeze 
bottle says?  Ofcourse not, it would be stupid to risk injury by 
presuming that.  Water is one of the most mild reagents available, 
infact it acts solely as a diluent to the vast majority of chemicals 
available.  It is only of concern where water reactive materials (such 
as alkali metals) are present.

Hence, you should first wash the board in water, if you keep deionized 
water flowing for long enough, it should remove almost all ionic species 
(excluding trace OH- and H30+), once this is completely done then you 
can (if desired) wash it with IPA to remove any trace residue.  This 
will ensure that the quantity of water miscible and alcohol reactive 
material will have been removed.

Sorry for being so long, and even posting on this thread which has more 
than enough differing opinions.
But I think all is dealt with now.

Regards,
Bevan