In this discussion I miss one aspect on the wetting performance of
HASL-treated boards.
And that is, if the blow-off by the air knive is too strong, solder
lands can have no or too little solder left on the surface. The inter
metallic surface is then exposed to the air and there is at least
strong acid flux needed for proper wetting in soldering processes
afterwards.
Fingerprints on such boards are desastrous. Skin fats and oils are
easily absorbed by the porous structure of the Cu6Sn5 intermetallic
layer. My experience is: never touch HASL-boards with bare hands.
So, be aware that there is enough solder left on the solder lands
(minimum +/- 8 um) after HASL-treatments.
Peer Langeveld
Consultant Soft Soldering Processes
5502 VH 8 The Netherlands
2008/3/24, Gervascio, Thomas <[log in to unmask]>:
> I would say that a mild acid etch probably would be more aggressive in removing a wider array of contaminates that the flux. Unless it is a inorganic acid flux (zinc chloride/HCl) even a water soluble flux would not be as effective in oxidizing and removing other soils prior to the HASL process. In addition, the acid bath probably can tolerate a higher soil load than a flux bath- so the bath would last longer and require less changeover (less raw materials and waste stream).
>
> From a contract assembler standpoint we would welcome it and a prudent measure. With Receiving Inspection not viewed as a "value added activity" most problems are now found on the production floor- how about that as a poor management philosophy but hard to predict rework so hard to justify the expenditures. Sorry will get off my soapbox.
>
>
> Tom
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Louis Hart
> Sent: Friday, March 21, 2008 12:07 PM
> To: [log in to unmask]
> Subject: Re: [TN] SV: [TN] preparation for HASL
>
> Thanks for your help, Inge. It got me thinking about greasy fingerprints, however. The engineers here tell me acid will not remove fingerprints. And this precleaning process uses acids. Supposedly alkaline cleaning removes fingerprints.
>
> Louis
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Hfjord
> Sent: Friday, March 21, 2008 11:04 AM
> To: [log in to unmask]
> Subject: [TN] SV: [TN] preparation for HASL
>
> Agree. Solder flux is for oxides, remember! Solder flux does not take grease! At least what I have learned. There may be formulas that take even grease, but we don't have them.
> /Inge
>
>
> -----Ursprungligt meddelande-----
> Från: TechNet [mailto:[log in to unmask]] För Lee parker
> Skickat: den 21 mars 2008 15:36
> Till: [log in to unmask]
> Ämne: Re: [TN] preparation for HASL
>
> Louis
>
> I would continue the process as you are currently doing. You can never be too clean or too rich.
>
> Best regards
>
> Lee
>
> J. Lee Parker, Ph.D.
> JLP Consultants LLC
> 804 779 3389
>
>
> ----- Original Message -----
> From: "Louis Hart" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, March 21, 2008 10:20 AM
> Subject: [TN] preparation for HASL
>
>
> TechNetters, a question has come up in our plant about cleaning copper surfaces before HASL. (Solder used is the standard tin-lead.) We've been putting panels through a light acid clean and etch, then through a Quicksilver flux applicator with two rollers that appear to be saturated with Enthone 757 SG flux. Someone has asked if that acid clean and etch are really necessary, since what is flux supposed to do?
>
> Any comments on the need for the acid clean and etch would be most welcome.
>
> Many thanks - Louis
>
> Louis Hart
> Compunetics
> Monroeville, PA
> USA
> [log in to unmask]<mailto:[log in to unmask]>
> 412-858-1272
>
>
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