Homebrew PCBs

Jeremy,

Thanks for the info,
I assume your plating solutions (including flash plate) were 
purchased as proprietary products. so I understand why you 
wouldn't know exactly what's in the mix. As for tin plating , you 
mentioned sulfuric acid, which would mean the tin is stannous 
sulfate { also called tin(II) sulfate or SnSO4} . Is the solution 
a milky white/yellow or pale brown color ? This is normal 
color(s) for this plating bath.

As for copper, I suspect you must be running a conventional acid 
copper bath to build up the copper to significant thickness. I 
understand the flash plate is primarily to get converge of copper 
inside the holes, after that, the copper is plated at high speed 
in acid copper. If you try plate too much from the 
alkaline/copper sulfate/sodium hypophosphite bath then you will 
consume too much copper and make bath maintenance difficult. I 
use carbon based method to prepare holes for electroplating in 
acid copper bath. I'm still experimenting with this.
A good overview on method of making holes conductive is at;
http://www.epa.gov/dfe/pubs/pwb/ctsa/ch2/ch2-1.pdf


If your anodes are 10% lead then all I suspect this will do is 
create a excessive black film over the anodes as they are 
consumed. The reason is lead sulfate formed during dissolution of 
the anode is completely insoluble and therefore will not plate on 
the PCB. In order to plate tin/lead you need the a different type 
of chemistry. For details on tin/lead plating see:
http://www.pfonline.com/articles/pfd0023.html

I must admit I haven't tested for solderability on one of my very 
old tin plated PCBs. The oldest one is about 2 years.
What I was saying about tin whiskers is if there has been real 
life problems with plated tin finish PCBs ? The NASA article on 
whiskers demonstrates whiskers problems on IC legs and 
connectors, but nothing on PCB's. I'm wondering if the solder 
reflow process eliminates the whisker problem since the tin is 
mixed with some lead from the solder. Very few PCBs are 
fabricated with pure tin as a final finish, but I'm curious if 
this the reason is because of the whisker problem.

Adam



Jeremy Taylor wrote:
> My tin setup is Sulfuric based, Tin stuff and Brightener
> The Tin is pattern plated at 100 milliamps per sq in (.0001 per 10 mins) I
> shoot for 0003~0004 "
> My tin Tank is 3 Gallons
> 
> The Flash copper is alkaline, mostly copper sulfate with hyposodium base and
> organics.
> The copper is panel plated, with 1 amp per 10 Sq In (.00025 per 15 mins)  ,
> I shoot for  a 0.0005" coverage
> My copper tank is 3 Gallons
> 
> The electroless Nickel is a bit complicated on keeping exact track of how
> much you have used. I know that it has Nickel in it,
> But other than that Its Part A, Part B, Part C and Water.  It must be HOT
> 195 Deg F.
> Plates very evenly  0.00025"  per 15 min. I shoot for .0003".
> The Nickel tank is 1/2 a gallon.
> My plating-dev-strip-etch, "system" is 32" wide X 8 feet long
> 
> 
>>I have never heard of problems of
>>electroplated tin creating whiskers. Do you have any knowledge of
>>tin whiskers being a concern in PCB production.
>>here is an interesting articles on tin whiskers.
>>
> 
> http://nepp.nasa.gov/whisker/reference/tech_papers/brusse2002-slides-tin-whiskers-attributes-mitigation-CARTS-europe.pdf<
> 
> I'm a little confuse by your statement. as the link you posted is absolutely
> a great resource on tin "whiskers" and even they end by recommending
> avoiding PURE tin. ... and that is what I've done with a 10% Lead content.
> 
> I'm not going to argue the merits of intermetalic alloy formation, lots of
> factual info already out there. 1 month is not very long, ,,, 3 Year is a
> good testing point.