Ingemar
What frequency did this occur? Does there seem to be a threshold frequency
below which this issue is essentially avoided?
Lee
----- Original Message -----
From: "Hernefjord Ingemar" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, June 14, 2007 4:18 AM
Subject: Re: [TN] Nickel barrier and RF applications
Now, Paymon's case was not a RF unit, but sort of a magnetic one, but as
many are interested in microwave issues I noted some matters years ago,
one connected to flux, the other to barrier layers. Sandia Labs had
something called 'Low Residue Soldering Task Force'. Dr Laura Turbini
and her group found a clear connection between the solder residues and
increased RF loss.
From her report: 'It has been shown that polyglycols and hydrobromic
acid (constituents in some fluxes)diffuses into epoxy during the HASL
process. Under the humid conditions of this test, these processing
chemicals may change the dielectric properties of the test board, which
affect the RF signal integrity.' 451
After that report and some others, we are more motivated to keep
critical RF boards as clean as possible. Normally, flux residues are not
an issue, but some regions of a circuit can be very sensitive to losses.
The other object is rare. I'll send two pictures to Steve's Wax Cabinet.
These show how NiCr leaked out from the edges of the hot RF line and
deposited on the substrate. Caused severe changes in the circuit's RF
properties. We have seen it just a couple of times. No explanation found
how this works. Mystery among many other RF mysteries. The only thing we
could verify was that the 'bleeding' NiCr coincided with the electrical
field.
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paymon Sani
Sent: den 13 juni 2007 17:38
To: [log in to unmask]
Subject: Re: [TN] Nickel barrier and RF applications
The boards are assembled with no-clean flux.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev
Sent: June 13, 2007 11:32 AM
To: [log in to unmask]
Subject: Re: [TN] Nickel barrier and RF applications
I'm not that sure about solder wetting larger areas after the second
re-flow. On ENIG it usuallyh covers pads right away (unless the re-flow
is screwed). As far as flux residue is concerne, then we don't know
whether they use water soluable or non-clean one.
Regards,
Vladimir
-----Original Message-----
From: TechNet
To: [log in to unmask]
Sent: Wed Jun 13 11:10:33 2007
Subject: Re: [TN] Nickel barrier and RF applications
As I stated in my previous response to Vladimer, you are doing both.
Solder flows along the traces during the first reflow, forming an IMF
with the nickel, and providing a path (more conductive path) for the
signal. After the second reflow, the solder joints wet out a little
further, and a very small increase in the IMF also takes place.
While any of these is a very small change, the cumulative effect of
reflowing all of the solder joints is usually enough to create a
detectable improvement in performance of the high-RF/high-impedance
circuit performance.
Getting rid of additional flux also helps.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paymon Sani
Sent: Wednesday, June 13, 2007 10:05 AM
To: [log in to unmask]
Subject: Re: [TN] Nickel barrier and RF applications
This is the million $ question. The assemblies are single sided with no
TH components. We simply pass them through the reflow oven for a second
time without changing the reflow profile or adding paste or flux to
improve the output power by 0.2 to 2 dB with majority of improvement at
0.5 dB! The question is what we are doing to the boards during the
second reflow:
1- Does it evaporate some of the flux residues?
2- Does it increase the IMC thickness?
The x-ray images of the before and after reflow are very similar, i.e.
we are not collapsing voids or creating new voids.
Paymon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev
Sent: June 13, 2007 10:39 AM
To: [log in to unmask]
Subject: Re: [TN] Nickel barrier and RF applications
I think, there is one question to ask. If ENIG (or rather the presence
of Ni) is the source of the problem, then why does 2nd reflow improves
the yield?
Regards,
Vladimir
AMD
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paymon Sani
Sent: Wednesday, June 13, 2007 10:34 AM
To: [log in to unmask]
Subject: Re: [TN] Nickel barrier and RF applications
Thank you Steve,
This sheds a lot of light on the current RF product failures at my
company. As a matter of fact, my PCB supplier is applying ENIG on all
copper surfaces before the mask application!
Paul, thank you for initiating this trend.
Cheers,
Paymon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: June 13, 2007 10:23 AM
To: [log in to unmask]
Subject: Re: [TN] Nickel barrier and RF applications
I just realized that the URL may have wrapped. Try this one:
http://tinyurl.com/2vjenp
This might be the same one that Inge was talking about....
Steve Gregory
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, June 13, 2007 9:00 AM
To: [log in to unmask]
Subject: Re: [TN] Nickel barrier and RF applications
Here's an article:
http://www.taconic-add.com/pdf/technicalarticles--effectsofsurfacefinish
pdf
Steve Gregory
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paymon Sani
Sent: Wednesday, June 13, 2007 8:57 AM
To: [log in to unmask]
Subject: [TN] Nickel barrier and RF applications
Hello John, is it documented anywhere?
Paymon
-----Original Message-----
From: John Burke [mailto:[log in to unmask]]
Sent: June 13, 2007 9:53 AM
To: 'TechNet E-Mail Forum'; Paymon Sani
Subject: RE: [TN] Plating
The nickel in enig is not good for frequencies above 3 - 4 GHz
John Burke
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paymon Sani
Sent: Wednesday, June 13, 2007 6:47 AM
To: [log in to unmask]
Subject: Re: [TN] Plating
Hello Inge,
This is very interesting! I did not make the connection between the
Nickel on the PCBs and the RF application. Are there any papers that
explain the sensitivity of RF applications to the Nickel barrier in ENIG
PCBs?
We are having trouble with a 5.8 GHz RF product right now. The assembly
meets the IPC-610D requirement. However, 25% of the products fail
testing. We reflow the failed assemblies for the 2nd time and 50% of
them pass testing! We do not know the RC of the failures. I was
suspecting the flux to be the root cause but could it be the Nickel
barrier?
Cheers,
Paymon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: June 13, 2007 2:33 AM
To: [log in to unmask]
Subject: Re: [TN] Plating
Paul,
Lockheed Martin use a lot of platings. I'm not sure, but I have seen
Boron as a barrier somewhere, just can't find it right now. Anyway,
Lockheed as well as NASA use many special platings. Non-magnetic, guess
you have a RF application that need low-loss lines.
http://supplier.external.lmco.com/supplier/po_information/specpro2.htm
I was myself looking for a non-magnetic finish once, and if I remember
right, there is a difference between EN and EN. The acidous electroless
nickel is not ferromagnetic, while alcaline electroless nickel is
somewhat ferromagnetic.
Borohydride electroless Nickel-Boron is probably non-magnetic too.
However, you should contact your plating chemist to verify, it was many
years since I mixed with this. (In earlier days, we had our own
chemists, many of them had piles of knowhow, but then came the
economist's era, and the chemists were kicked out)
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stolar, Paul W
Sent: den 12 juni 2007 23:38
To: [log in to unmask]
Subject: [TN] Plating
We are using nickel as a barrier metal on a PC board for the pads.
Are there any other barrier metals we can use which are non-magnetic.
Bare copper is not an option.
Paul Stolar
Materials/Reliability Engineer
Manufacturing Reliability Lead Engineer
Baker Atlas
713-625-5376
713-625-4949 (fax)
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