Hi Yoyce,
I started this issue of the Nickel-Gold measurements,so let add my 2 cents
conserning destructive methods.
1) the method is destructive,allows measuring of one spot at time and takes
at least two to three hours.It can not be used quick in-production
measurements such as for tab plators.
2) You are right about nickel overplating,otherwise the gold edge is
"smeared"
3) The thickness of the gold on tabs is in range from 0.75 to 1.3
microns.The resolution should be 0.1 microns and this is far below
possibilities of optical inspection
Regards
Edward Szpruch
Eltek , Manager of Process Engineering
P.O.Box 159 ; 49101 Petah Tikva Israel
Tel ++972 3 9395050 , Fax ++972 3 9309581
e-mail [log in to unmask]
> -----Original Message-----
> From: joyce [SMTP:[log in to unmask]]
> Sent: ד אוקטובר 06 1999 2:46
> To: [log in to unmask]
> Subject: Re: [TN] Measurements of Gold over Nickel
>
> few points:
> (1) cross section of Au/Ni/Cu should be done with Ni over plating on top
> of
> the Au prior to cross section mounting. the cover layer can be any hard
> metals, what ever you can easily put it on top of the Au without damage
> the
> surface features. The Ni would prevent the smear of Au layer. The cross
> section not only show the Au thickness, it also reveal the morphology of
> the
> grain and grain boundary structure, columinar or equiaxial. Most
> importantly, it shows the interfacial structure of Au/Ni/Cu. If the
> interface is porous, the Cu will diffuse to the top surface and make poor
> reliability products. Plating parameters are important to achieve the
> flat
> dense interface, uniform coverage and good quality Au/Ni layers. (I guess
> all the plating experts will tell you more about the current density, pH,
> tank design, edge flux distortions, organic additive entrapment, etc.
> much,
> much more than I do).
> (2) The reasons for XRF and cross section measurements have some
> discrepancy
> are:
> (a) porosity of the plating compare to the calibration sample. The
> calibration sample (coupon) normally made by dense, uniform Au over Ni.
> The
> actural measurement done on the PCB sometimes are not as uniform at the
> interface and exist some porosity.. This is more problmatic when immersion
> Au is used. Since the immersion is based on atom (ion) exchange process,
> the thickness of Au has a layer of mixed Ni/Au plus some organic
> additives.
> It is rather difficult to define where exactly where the interface is when
> cross sectioned. Porous plating (e.g. columinar grain in electrolytic Au)
> normally gave a thicker reading on cross section data than the XRF
> measurements.
> (b) Correct me, if I am wrong, based on my understanding, the immersion
> Au
> is less dense than the "properly" electrolytic plating Au. Some of the
> discrepancy is due to the density difference between the calibration
> sample
> and the immersion Au. (The XRF is based on the absorption edge of the
> charcteristic X-ray, the thickness calculation is based on the number of
> the
> atoms/unit volume using calibration samples).
> (c) wrong calibration sample (even the same stacking sequence,e.g.
> Au/Ni/Cu,
> but different thickness) may raise the error. (sometimes, we only have
> limited calibration samples on hand... you have do some "fancy foot work"
> in
> order to get the actual measurement... particularly, for the new stacking
> sequence of material...)...If you can't trust your equipment, you might as
> well forget the measurement.
> ....this is just my limited understanding of the issue (1 cent)...
> hopefully, someone will give their insight (millions).
> jk
>
>
>
> At 10:11 AM 10/5/99 -0700, you wrote:
> >I'm not a PWB shop person, but I've supported many in the past. I'm not
> >sure the shops are set up for 0.5um resolution. I'm not comfortable with
> >those Beuer polish set ups for 1um resolution, but I don't know the
> product
> >in detail. I'd like to know if there is a need and I'll send in my
> >suggestions (as one who has done microscopy 1nm-10um samples on a
> research
> >basis for years). But I'll save that lengthy verbage for later.
> >
> >I've found cross-sections can be very misleading because of metal smear
> at
> >thicknesses of ~1um. It is critical that the last polish be done
> parallel
> >to the interface of gold/nickel with much care. I'm not a fan of the XRF
> >technique because it relies on mathematically modeling your metal system-
> >perfectly flat interface, no thickness variations over sample area, and
> the
> >interactions for fluorescence in each layer.
> >
> >I suggest you do some hard work up front, but then it will become routine
> >and easy later: find a selective etch for gold or nickel (you'll probably
> >have more luck with the latter) or one that highlights the interface
> (takes
> >advantage of that mismatch of metal-metal interface...back to that wire
> >bonding story, Inge!). This also means, you can't just put your sample
> on
> >the automatic polisher without paying good attention to the last step.
> You
> >may do it by hand using 600 grit (I think that is per square inch)
> followed
> >by 1000 grit sand paper. A true polish (<0.2 um in your case) may be
> >needed, but I'd try to avoid it because it's a hassle to keep a clean
> plate
> >for that. And don't contaminate your polish plates with dirty parts
> >holders.
> >
> >
> >
> >-----Original Message-----
> >From: TOE /Torben Osteraa <[log in to unmask]>
> >To: [log in to unmask] <[log in to unmask]>
> >Date: Tuesday, October 05, 1999 1:05 AM
> >Subject: Re: [TN] Measurements of Gold over Nickel
> >
> >
> >Ingemar, and others:
> >While we're on the subject:
> >We also use 'stoneage' technique to inspect nickle/gold
> >plating from sub-contractor. He's using some sort of
> >non-destructive method to verify thickness, and we do not
> >always agree on the result.
> >Apart from the obvious problem of thichness variation over
> >the panel, is there a predictable difference in thickness
> >found using different techniques?
> >
> >Regards
> >
> >Torben Osteraa
> >Printca AS
> >Denmark
> >
> >
> >>>-----Original Message-----
> >>>From: Ingemar Hernefjord (EMW)
> >>>[mailto:[log in to unmask]]
> >>>Sent: Tuesday, October 05, 1999 8:42 AM
> >>>To: [log in to unmask]
> >>>Subject: Re: [TN] Measurements of Gold over Nickel
> >>>
> >>>
> >>>Edward,
> >>>we have found that there is nothing better than ordinary
> >>>stoneaged crossectioning and study in a metalographic
> >>>microscope. In mass production, samples are usually enough.
> >>>Such examinations don't take time and they tell a lot more
> >>>than betascope. And...you can store the images and have a
> >>>look back up and then.
> >>>Regards
> >>>Ingemar Hernefjord
> >>>Ericsson Microwave Systems
> >>>
> >>>
> >>>I am looking after alternative method of measuring of
> >>>electroplated Gold
> >>>over Nickel for production .Gold thickness is in range from
> >>>0.75 to 2.5
> >>>microns.
> >>>I have in my plant beta scope with Promethium source with lot
> >>>of problems.I
> >>>have also XRF,that can not be placed in production area.
> >>>Any sugestions?
> >>>
> >>>Edward Szpruch
> >>>Eltek , Manager of Process Engineering
> >>>P.O.Box 159 ; 49101 Petah Tikva Israel
> >>>Tel ++972 3 9395050 , Fax ++972 3 9309581
> >>>e-mail [log in to unmask]
> >>>
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