My original question came out of curiosity from one of Lee Ritchies fab notes stating a max of 15 micro inches of electroplated gold be applied over electroplated nickel. We had historically called for a max of 8 micro inches of immersion gold to be applied. I was curious why either max would be called out and why as I would prefer to just call out the min requirement as per 4552
-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Stadem, Richard D
Sent: Monday, January 6, 2020 7:36 AM
To: [log in to unmask]
Subject: Re: [TN] [External] [TN] immersion gold thickness
In addition to the black pad issues Dave mentioned, the 5 uinch limit was also to provide sufficient plating thickness to prevent oxidation of the underlying nickel, which is what you actually solder to, as well as prevent gold embrittlement in the final solder joints.
At least 2 uinches is required to provide the protection, but you certainly do not want anything over 5, and never 15 uinches. I am not even sure it is possible to get 15 uinches in an immersion plating process. But whatever process that gives you 15 uinches is NOT electroless nicker/immersion gold.
Odin
-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of David Hillman
Sent: Friday, January 3, 2020 3:44 PM
To: [log in to unmask]
Subject: Re: [TN] [External] [TN] immersion gold thickness
Hi Murray - if you can get a true ENIG plating chemistry to put 15 inches of gold thickness on a board, you would never want to use the board as the gold plating would have severe structure and/or solderability issues. The IPC-4552 specification contains the industry consensus gold plating thickness range that applies to producing an acceptable and reliable ENIG plating layer. Any gold plating thickness outside of that range would be questionable at best for quality and reliability unless you are working closely with a plating chemistry supplier who is doing a custom plating bath composition. One of the early issues of ENIG plating was the industry asking the plating chemistry suppliers to provide an immersion gold plating thickness that exceeded the acceptable physics of the plating chemistry (basically this is how we discovered "black pad"!).
Dave Hillman
Collins Aerospace
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On Fri, Jan 3, 2020 at 3:30 PM Campbell, Murray <[log in to unmask]>
wrote:
> Happy New Year All,
>
> Is there any good reason to call out a maximum gold thickness / nickel
> thickness on fab notes or is it sufficient to rely on simply stating
> that the fabricator shall follow ipc-4552 minimum thickness? I have
> seen some companies state that a maximum thickness upwards of 15 µin
> to be acceptable. Is there any value in stating an upper range?
> I know it states in 4552 that an upper range had been debated and not
> necessary but I still see an upper added to fab notes.
>
> Regards,
>
> Murray Campbell
> PCB Design Specialist
> [log in to unmask]<mailto:[log in to unmask]>
> [cid:[log in to unmask]]
>
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