Is the product assembled lead-free or with Pb/Sn solder?
Our experience is that ENIG boards have a very long shelf life without any special packaging. We have not had any black pad problems since we began using this finish in 2003. Our vendor in the SF bay area, Bay Area Circuits in Redwood City, CA does an excellent job making these boards.
Some prefer immersion silver but I don't like fact that you have to seal it in bags to prevent SO2 and other environmental gases from tarnishing the finish.
I've recently heard that immersion tin plating can grow a forest of tin whiskers. While I have no personal experience with immersion tin, as prior to switching to ENIG for coplanarity problems with SMT parts we used HASL, the immersion tin problem has been mentioned to me by several people.
I'm interested in hearing from anyone else who's experienced whiskers on a board finish.
Bob Landman
H&L Instruments, LLC
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Uppina Nagaraj
Sent: Thursday, June 17, 2010 8:05 AM
To: [log in to unmask]
Subject: Re: [TN] Query on shelf life of PCBs & impact on solderability
Hi Bev,
Thanks for the quick reply and inputs.
The product that I've written is built to IPC-6012, Class B.
Best Regards,
U.Nagaraj
> Uppina,
> Wow! LOTS of questions. I can only answer some.
>
> 1) Yes, generally ENIG boards store better than HASL boards. HASL
> board solderability decreases because of growth of oxide and growth of
> intermetallic. If the HASL layer is thin the intermetallic can reach
> the surface sooner and then, well, it ain't going to solder.
>
> Vacuum packing can increase the shelf life of finishes that can oxidize.
> This assumes excellent packaging, not stored so long there are
> intermetallic problems, etc., etc.
>
> For a lot more on this get the IPC series of docs on surface
> finishes. I can't remember the numbers, but I am sure someone else
> will respond with those.
>
> 2) Photos to TechNet get stripped out. Either sent to Steve Gregory
> or post on the IPC site.
> Question to you: what IPC class of product are you building?
>
> Bev
> RIM
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Uppina Nagaraj
> Sent: Thursday, June 17, 2010 7:30 AM
> To: [log in to unmask]
> Subject: [TN] Query on shelf life of PCBs & impact on solderability
>
> Dear All,
>
> I have 3 queries in all.....
>
> 1. One of our customer has changed the surface finish from HASL
> to ENIG. Their main reason for this change was that they
> have had a bad experience with storage of HASL finished boards
> (the reason for which is not shared with us). They had encountered
> solderability problems on the HASL finished board which they
> had stored for a period of time.
>
> Their expectation with Gold plated surface is the storage
> of the PCBs can be for a longer period of time as compared to
> HASL finish.
>
> Initially they had a requirement for 1micron thick electrolytic
> gold, but later on they changed the requirement for an ENIG process
> with gold around 0.05 to 0.10 microns.
>
> Now my question......
>
> Is there any guideline on the shelf life of the PCBs (with regard
> to
> solderability) of the following surface finishes....
>
> a) ENIG
> b) HASL
> c) Immersion Tin
> d) Electrolytic Ni and electrolytic gold with Gold thickness
> of 1.0microns
>
> Will vacuum packing help to extend the shelf life?
>
> 2. One of our customer is doing hand soldering of PCBs with ENIG finish.
> They're inserting a strand of tinned Copper wires from component
> side and later on using soldering iron to do the soldering from the
> solder side.
>
> The solder is able to flow up from solder side to component side,
> but the solder is unable to complete wet the pad on the component side.
>
> I've attached the photos of example of the phenomenon. These photos
> are without the wire, I've just used bare PCBs to do the soldering to
> illustrate the phenomenon.
>
>
> Now my question....
>
> a) Will increasing the volume of the solder help in complete wetting
> of the pads on the component side?
> b) Any other way to get a full coverage on the pads on the component
> side.
>
> 3. This question is about the same customer which I've mentioned in
> para 2 above, is doing hand soldering. In one of the stage of
> component assembly, they're (hand) soldering a flexible PCB
> on the ENIG finished rigid PCBs.
>
> They have a unique practice during this stage of soldering. They've
> explained to us that this particular component is very sensitive to
> high temperature and hence the soldering iron temperature is set at
> 210Deg C. They're using Sn60/Pb40 solder for this soldering operation.
> After the soldering iron achieves 210Deg C, they're turning off the
> power to the soldering iron and doing the soldering of the flexi PCB
> onto the rigi PCBs. We'll not know the actual
> soldering iron temperature at the point of contact.
>
> They've complained to us that the soldering is poor.
>
> We know that the melting temperature of solder is around 183deg C.
> But,
>
> is there any guideline on the minimum temperature for soldering to
> get a good flow of solder and completely wetted solder?
>
> Thanks for your inputs in advance.
>
> Best Regards,
> U.Nagaraj
> MICROPACK Ltd,
> Bangalore, INDIA.
>
>
>
>
>
>
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