I know you were asking Mike to reply so pardon me. There will come a day
when we will not be allowed to use lead or any combination thereof. We
changed to tin as an overplate before etch in 1982. If you are still
needing to plate and hot fuse tin/lead until the deadline, do it. After you
have to quit shipping out tin/lead, you should have the BAT ready to go in
service. The spent solution from stripping pure tin is less expensive to
reclaim and regenerate as well.
At 01:41 PM 10/14/2005, you wrote:
>Mike:
>I don't think I would want to get into this process where the operation
>window is so tight.
>My next question is than why even bother going from tinlead to tin since for
>lead free you are stripping tinlead anyway and providing other finishes
>other than HASL.
>Sona
>
>
>----- Original Message -----
>From: "Barmuta, Mike" <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Friday, October 14, 2005 2:15 PM
>Subject: Re: [TN] Electrolytic Tin Plating
>
>
>>Sona: Back in the "old" days we did a lot of tin plating as the final
>>finish
>>on Teflon MLB's, typically for high frequency signal generators. You
>>definitely didn't want to mess these up or it could get real expensive
>>rear
>>quick.
>>
>>It's a very tricky process but if all factors are controlled properly it
>>works. Unfortunately most people doing tin plating these days are only
>>using
>>it for etch resist and are not aware of the multiple issues needed to
>>produce an acceptable electroplated tin final finish.
>>So let me give you some pointers on how we did it.
>>
>>1. Bath Type: Lea Ronal(Rohm and Haas) Bright Acid Tin Sulfate
>>Electrolytic
>>Plate. This is a fine grain structure finish not requiring any type of
>>reflow processing. Due to low porosity and tight grain structure of the
>>deposit it is not as susceptible to staining as a matte/semi-mate tin.
>>
>>2. Underplate: To help prevent slivering you need an electrolytic nickel
>>underplate between the copper and tin
>>
>>3. Rinsing: To minimize staining after tin plate you need multiple rinses
>>cold followed by hot. Any acid drag over in final rinsing will result in
>>staining.
>>
>>4. Resist Strip: The resist stripper chemistry has to be designed for
>>compatibility with bright tin, if not you will get staining.
>>
>>5. Etch: You need to control your etcher(ammoniated), pH, chemistry, temp,
>>speed, etc, to minimize undercut which will produce slivers. Again rinsing
>>is critical here too.
>>
>>6. Soldermask Prep: Do not scrub the panels.
>>
>>7. Soldermask Bake: Bake at 140C for 60-80 mins AT temperature. If you
>>have
>>discoloration you probably have done a poor job of rinsing somewhere above
>>or have poor water quality. Poor air circulation in the oven can also be a
>>cause.
>>
>>8. Tin Plate Bath Control: Control of the multiple component organic
>>brightners, levelers and grain refiners is critical. Also the stannic,
>>stannous, sulfuric acid constituents, cathode agitation, amount/velocity
>>of
>>filtration, trace metal impurities, organic build-up, etc, need to be
>>monitored and properly controlled.
>>
>>
>>If done right the end result will be an acceptable product but screw up
>>just
>>one factor and you will have garbage. You need to ask yourself how much
>>you
>>are willing to commit to offer this type of final finish and is it worth
>>it.
>>
>> Regards
>>
>>Michael Barmuta
>>
>>Staff Engineer
>>
>>Fluke Corp
>>
>>Everett WA
>>
>>425-446-6076
>>
>>
>>
>>
>>-----Original Message-----
>>From: TechNet [mailto:[log in to unmask]]On Behalf Of Fineline Circuits,
>>Inc
>>Sent: Friday, October 14, 2005 9:39 AM
>>To: [log in to unmask]
>>Subject: Re: [TN] Electrolytic Tin Plating
>>
>>
>>Colin:
>>2-3 years back we ran an experiment with a tin vendor where we did
>>electrolytic tin plate, etch, and mask.Tin was supposed to be the final
>>finish per vendor.Vendor told us that he had customers that did this.
>>However the tin got tarnished and dark grey after cure and we just did not
>>like the look off the final finish. We did not pursue it further.
>>Sona
>>
>>----- Original Message -----
>>From: "Colin McVean" <[log in to unmask]>
>>To: <[log in to unmask]>
>>Sent: Friday, October 14, 2005 10:33 AM
>>Subject: Re: [TN] Electrolytic Tin Plating
>>
>>
>>Are you suggesting that you use the tin plate as your final finish? I'm
>>no chemist, but I think that could spell trouble, with the open
>>structure of the electroplated tin giving rise to whiskers.
>>We use Electroplated tin, but only for the etch resist application - we
>>strip it off, solder mask, then final finish, either Immersion Silver,
>>Immersion Ni/Au, or lead free HASL dependant on customer requirements.
>>
>>Colin McVean M.Inst.C.T.
>>Production Manager
>>Artetch Circuits Limited
>>Main: 01903 725365
>>DD: 01903 712926
>>Email: [log in to unmask]
>>www.artetch.co.uk
>>-----Original Message-----
>>From: TechNet [mailto:[log in to unmask]] On Behalf Of Fineline Circuits,
>>Inc
>>Sent: 14 October 2005 15:20
>>To: [log in to unmask]
>>Subject: [TN] Electrolytic Tin Plating
>>
>>Hi Technetters:
>>Now that Leadfree is here or close to, we would like to change the
>>electrolytic tinlead plating tank to electrolytic tin tank.
>>I would like to know if the other fab houses have done this and if so
>>which
>>vendors tin chemistry has a wider window of operation. Are they seeing
>>any
>>tin whiskers/sliver problems etc..especially if the boards are stored
>>for
>>few months.
>>Also it is my understanding that you can mask over this plated tin since
>>it
>>does not flow. In this case you can totally avoid stripping the tin and
>>tin
>>levelling.
>>We currently do offer other finishes including electroless tin ,
>>immersion
>>nickel/gold, silver....
>>If there are other consideration in making this change I would
>>appreciate
>>your input.
>>Franklin, like you I would like to see more fab houses participating but
>>I
>>would like to remain with technet.
>>Thanks
>>
>>Sona Sitapara
>>Fineline Circuits Inc.
>>
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