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August 2014

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From:
"Larson, Mark" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Larson, Mark
Date:
Mon, 18 Aug 2014 13:16:43 +0000
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OK, I have a sample and it doesn't even look like copper, what would the material be? It kind of looks like silver, and to keep the guessers at bay, yes, I have scratched it, no it isn't the plating that is silver, it is the base metal and it looks like there *could* be a finish, if it is indeed a finish it is kind of yellow. The material is Rogers 4350 or similar

-----Original Message-----
From: Wenger, George M. [Contractor] [mailto:[log in to unmask]] 
Sent: Friday, August 15, 2014 5:21 PM
To: TechNet E-Mail Forum; Larson, Mark
Subject: RE: [TN] surface finish for "bare" copper

Mark,

I've worked on antenna boards I think that are similar to what you've described (i.e., cheap, simple double sided PCBs without PTHs).  The boards I've worked on did have a few hand soldered resistors and some RF input and output cables.  The surface finishes on antenna boards I've worked on have been either immersion tin or bright electrolytic silver plating.  The reason I was involved in working on them is because the antenna boards that had immersion tin surface finish had self life and solderability issues and the bright electroplated tin boards, which didn't have shelf life and solderability issues, had tin whisker issues.

My advice for a surface finish for cheap, double sided antenna boards would be immersion silver.  There are a lot of OSPs on the market that probably would work on antennas but then you have to worry about how well the OSP will survive environmental exposure and since you're talking antenna boards I have to assume they are outdoor exposure and the outdoors could be anywhere in the world.  I won't go into a detailed explanation on TN again about why immersion silver is my surface finish of choice but if you use a bare copper board I'm sure the bare copper antenna boards will oxidize during implement and copper oxide isn't a good RF conductor.  OSPs might be okay but they degrade when exposed to acidic or basic environments or can thermally degrade. Unlike copper, silver oxides are conductive and in all of the years we've been involved with quality and reliability of wireless products I've never had any issues with PCBAs with immersion silver surface finish.

Regards,
George
George M. Wenger
Failure Signature & Characterization Lab LLC
609 Cokesbury Road, High Bridge, NJ 08829
(908) 638-8771 Home  (732) 309-8964 Mobile E-mail [log in to unmask] [log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Larson, Mark
Sent: Friday, August 15, 2014 3:49 PM
To: [log in to unmask]
Subject: Re: [TN] surface finish for "bare" copper

I can answer my own question, Benzotriazole is OSP


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Larson, Mark
Sent: Friday, August 15, 2014 2:36 PM
To: [log in to unmask]
Subject: Re: [TN] surface finish for "bare" copper


Anybody hear of "Benzotriazole"?


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Friday, August 15, 2014 2:03 PM
To: [log in to unmask]
Subject: Re: [TN] surface finish for "bare" copper

Most RF antenna guys get a little too crazy about this. Up to about 10GHz I see a lot of ENIG used without complaint. If you want to see someone freak out, go ahead and put a conformal coat on the traces!

The original fabricator talking about bare copper may have been referring to a chromate anti-tarnish, which is often on the FR4 panels as delivered to the fab. That will hold up for quite a while also, but I don't know if it can be applied post-fabrication.

Nickel has poor RF performance. Ag oxidizes and will eventually look ugly, but the performance will probably be good for a long time, particularly with some anti-tarnish applied. Direct Au over copper might be something to consider.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Yuan-chia Joyce Koo
Sent: Friday, August 15, 2014 2:43 PM
To: [log in to unmask]
Subject: Re: [TN] surface finish for "bare" copper

(1) you need radar guy (2) my guess would be Ag.
just a guess.
   jk
On Aug 15, 2014, at 2:37 PM, Larson, Mark wrote:

> Thank you but I guess I should have been more clear, there are no 
> components and no holes on this board, it is an antenna board, I'm 
> pretty sure, a couple decades ago perhaps, I had a similar situation 
> and I ordered bare copper because that's what the engineer said, I got 
> a call from the fabricator asking, no, make that telling me, we really 
> didn't want that. Maybe finish isn't the right word, treatment 
> perhaps, he said the copper could be treated with something that would 
> prevent oxidizing. I think it was part of their normal process before 
> applying HASL, but maybe with lead free it is no longer used.
>
> Maybe I could ask the question, what would you apply to prevent 
> oxidation yet not affect the performance of the antenna in the several 
> GigaHertz range.?
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Yuan-chia Joyce 
> Koo
> Sent: Friday, August 15, 2014 1:04 PM
> To: [log in to unmask]
> Subject: Re: [TN] surface finish for "bare" copper
>
> agree with steve 100%.  It also depend upon your assembly condition:
> flux activity, number of reflow, reflow profile, subsequent exposure 
> to environment.... your design group should pick and choose the right 
> finishing... not on the MFG floor... my 2 cents.
>                  jk
> On Aug 15, 2014, at 1:55 PM, Stephen Gregory wrote:
>
>> To add to Wayne's input, make sure you call out the right OSP 
>> depending on the board technology...not all OSP's are the same.
>>
>> Steve
>>
>> Sent from my BlackBerry 10 smartphone.
>>   Original Message
>> From: Wayne Thayer
>> Sent: Friday, August 15, 2014 11:28 AM
>> To: [log in to unmask]
>> Reply To: TechNet E-Mail Forum
>> Subject: Re: [TN] surface finish for "bare" copper
>>
>> OSP
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Mark Larson
>> Sent: Friday, August 15, 2014 1:12 PM
>> To: [log in to unmask]
>> Subject: [TN] surface finish for "bare" copper
>>
>> Hi,
>>
>> I've got a board that needs bare copper, many years ago I had this as 
>> well and seem to recall that they can put on some kind of finish in 
>> the process that does not leave it bare, but does protect it in the 
>> processing of the board, and consequently does offer some protection 
>> to the end user.
>> Anybody know what
>> that is or how I call it out?
>>
>> --
>>
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