Hi Mike,
To 'repair' your hasl'd board with ENIG will require the supplier to
firstly strip off the reflowed solder, which is not easy. The chemistry
involved in removing the intermetallic will also attack the underlying
copper (because the intermetallic is CuxSnY). The ENIG process also has an
etch stage in it to activate the copper surface prior to the catalyst stage,
so I would be wary of the copper thickness in those important via holes,
where it is most difficult to strip solder, and solutions become trapped. As
a further complication, some electroless nickel baths use lead as a
stabiliser, so any solder residues will screw the bath. The theory says it
is possible to do this rework, but the practise suggests otherwise.
Dougal Stewart
email: [log in to unmask]
phone: +44 1896 822204
mob: +44 7984 629667
----- Original Message -----
From: "Michael Bell" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, September 25, 2002 10:40 PM
Subject: [TN] HASL/Gold Finish
> Hi all,
>
> We have just had a quote from one of our PCB manufacturers to repair a
HASL
> PCB and make it a Gold finish. Is this possible??? It was my assumption
> that once a PCB had a HASL finish, there was no way to back track and get
an
> emmersion gold finish???? Am I incorrect???? Could someone please
clarify
> this for me????
>
> Cheers
>
> Mike
>
> -----Original Message-----
> From: Kathy Kuhlow [mailto:[log in to unmask]]
> Sent: Tuesday, 24 September 2002 10:13
> To: [log in to unmask]
> Subject: Re: [TN] HASL
>
>
> What types of parts are causing the most problems? For parts that are
very
> fine pitch, tsops, etc we usually do not use a HASL finish. I prefer a
> immersion gold but hate osp's. HASL finishes have too wide of a process
> window for these devices. I see much flatter surfaces with alternate
> finishes. This is especially true with fine pitch on both sides. Most
> suppliers can control one side fairly well but two sides and it is much
> harder. The only supplier I have seen do this with a mediocre yield was
> utilizing a horizontal HASL process. Unfortunately most PCB houses use
> vertical HASL processing.
>
> Just my $.02
>
> Kathy
>
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