Hi,
Is there any risk after assembly, if the immersion silver PCB will be RTV
sealed in inert environment?
Which Pad to Pad Clearance required for reducing risk of electrochemical
migration ?
Anat
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Maurice Dore
Sent: Wednesday, May 27, 2009 9:36 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion Silver
Steve
Good place to start is IPC4553 - Silver tarnishes in the presence of
sulfur (Ag2S forms on the surface);
a. Storage & Handling
Handling- Gloves worn by Operators at all stages of production
1. Immersion silver boards should be packaged as soon as possible, to
prevent exposure to chlorides and sulfides in the air.
2. Use sulfur free, pH neutral paper to wrap stacks of parts and then
plastic wrap. Storage should be in sealed bags or sealed containers to
eliminate direct contact with air.
3. Wrapped packages should be stored below 30°C (86°F) and 75% R.H.
4. Do not use desiccant in the packages. Desiccant can contain sulfur
compounds.
5. Adhesive tape, adhesive labels, stamps, markers and rubber bands are
forbidden on silver boards and the sulfur free paper. They all contain
sulfur bearing compounds that will tarnish the silver coating.
6. If the original package is opened and not all of the boards consumed at
the EMS/OEM, they should be re-wrapped as soon as possible and returned to
a storage condition, preferably not-to-exceed 30°C (86°F) and
75% R.H.
b. Shelf Life
- Controlled Shelf Life in unopened Vendor packaging - 6 months and 4
weeks resealed Vendor packaging
- Floor Life - Double Sided Reflow - 48 hrs max
- Floor Life - to complete all solder assembly (i.e. wave solder) - 7 Days
maximum Floor Life
c. Corrosion Prevention
- Pads are non-soldermask defined, reduces risk of any creep corrosion
? Pad to Pad Clearance reduces risk of electrochemical migration
? PCB Supplier to observe ImmAg Thickness ( 0.2 - 0.4µm )
The key is to reduce exposure time to sulfide and chlorides (remember to
check both site levels) - I noticed solderability issues after 14 days
exposure time that affects our wave soldering process. logistics of moving
between manufacturing sites should be ok if controlled as recommended.
Rgds
Moss
Steve Kelly <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
26/05/2009 22:00
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Subject
[TN] Immersion Silver
Good Afternoon,
Any concerns about using immersion silver as a finish. PWB has to take two
reflow cycles, 1 re-work cycle and one hand solder after the two reflows.
Parts have to be transported from one part of the country to another after
the two reflows. Thanks. Steve Kelly
Steve Kelly (PLEASE NOTE NEW E-MAIL ADDRESS)
(416) 750-8433 (work)
(416) 750-0016 (fax)
(416) 577-8433 (cell)
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