Jeremy Taylor wrote:
> This is Solderon BHT-90 series
Ok, that clears up the confusion. If you say it contains sulfuric
but can also plate tin/lead so then the it must have some other
electrolytes for solubility of Pb.
> The surface of the plated tin does turns black in the etch, but a quick rub
> with a scotchbright cleans it up nicely
Yes, a darkened tin is normal after etching in
peroxy/sulfruid/copper sulfate. Alkaline ammonia etching is the
only etchant I know that has no effect pure tin or tin/lead.
Unfortunately persulfate etchants are too aggressive on pure tin
plating resists to make them usable.
> I only plate flash copper, No acid copper - not anymore anyhow.
> It works perfectly
So it sounds like you have the copper process sorted out for
yourself. I don't know of advantages there are with alkaline
copper plating, except for plating copper on metals like iron
which react in acid copper baths. The acid copper plating is the
standard bath for electroplating the bulk of copper on PCBs. With
brightener the "throwing power" of this bath is perfectly
adequate for most PCBs. Only when you get to very high aspect
ratio holes (0.1mm diameter 1.6mm deep) is when the solution
kinetics begin to fail plating uniform holes without slowing down
the plating speed. As I understand this is where efforts of pulse
plating come into effect. The acid copper is the best bath for
"throwing power" due to the high conductivity of sulfuric acid,
hence the relative large concentrations 200g/l H2SO4 typically
used. Brightener and leveling agents complete the bath
ingredients and produce amazing results compared to conventional
a non-bright low acid high copper bath. If alkaline plating is
working for you then I see no reason to change.
I have one question about copper baths. I get the impression you
have experienced both acid copper and alkaline copper baths in
your process. Did you find that the copper plating inside the
holes (i.e. over the ink) gave superior hole wall coverage with
the alkaline bath than it did with the acid bath ? Was the hole
wall coverage more complete after a given plating time (say after
5 minutes), thus giving less voids and more reliable through holes ?
If the ink utilizes graphite particles for conductivity then I
suspect the alkaline plating may have some interesting effects on
the platability over the ink compared to acid copper plating.
Adam
> Flash copper. small particle density, thus giving the kind of thru plating
> you could only get with high powered pulsed acid copper. I haven't noticed
> any increase in anode usage. as the organics keep the suspended copper in
> check. The plate actually comes from what's suspended. The anode dissolves
> as needed in to the solution. I have to keep a pump going to keep the
> copper suspended as ph fluctuates, as it's very near the point of copper
> sulfate precipitation. I use whatever is in the ink that Think and tinker
> sell, I thought it was silver based, but it's black like carbon. ... which
> makes me wonder why it costs what it does.
> I think the biggest diff noticeable for acid vs. flash - would be the
> hardness of the finish. But this is of little consequence to a pcb.
> Acid is faster. and easier to maintain. (cheaper too) but I like the flash
> much better for this application.
> I asked another group about this some time ago, and the only result I got
> was a recommendation for Electroless!
> My copper solution is green.
>
> I would probably keep the acid, If I wasn't plating tin.
>
> (whenever I use the term tin assume I mean SnPb)
>
> Yes everything I'm using is "store bought" not diy. I have about 20
> different testing solutions (Broh. Blue, Pan ind, EDTA Tet sodium, mercuric
> nitrate!! ,silver nitrate,nitric acid, etc... and related lab equipment to
> fully test all components of all solutions.) I'm really trying to keep a
> Very very low effluent.
>
> ∗Most pcb thru history have been SnPb, I assume Nasa was assuming this as
> well, pure Tin is pure Tin, and will do as pure tin does, no matter where it
> is. I suspect the whiskers would be more of a problem on high density
> layouts. I just err on the side of caution, as my product is a life support
> device ... for reef aquariums : )
>
> I still have my pure bright tin setup, actually expecting another on here
> soon, but I'm using it for other stuff, (emi shield on plastic housing)
>
> JT
>
>
> ----- Original Message -----
> From: "Adam Seychell" <adam_seychell@...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Thursday, April 01, 2004 7:19 PM
> Subject: Re: [Homebrew_PCBs] plated tin as the etch resist
>
>
>
>>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.
>>
>>
>>
>>
>>
>>Be sure to visit the group home and check for new Bookmarks and files:
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>>Yahoo! Groups Links
>>
>>
>>
>>
>>
>
>
>
>
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