Erik, your summary is great and I also want to thank everyone for the discussion.
It looks like there is no way we can "fundamentally improve" the Ni3Sn4/phosphorus enriched layer interface (I put "phosphorus enriched layer" instead of the original Ni3P in the Erik's summary, because it seems like it should to be a mix of the Ni3P and nickel), or am I wrong and there is a way to "defeat" nature ?
Best regards,
Vladimir
Vladimir Igoshev, Ph. D.
Materials Researcher
Research in Motion
451 Phillip St.
Waterloo, ON, N2L 3X2
Voice: (+1) 519-888-7465, ext. 5283
Fax: (+1) 519-886-0863
E-mail: [log in to unmask] <mailto:[log in to unmask]>
-----Original Message-----
From: Automatic digest processor [mailto:[log in to unmask]]
Sent: Saturday, December 14, 2002 1:00 AM
To: Recipients of Leadfree digests
Subject: Leadfree Digest - 12 Dec 2002 to 13 Dec 2002 (#2002-157)
There is one message totalling 722 lines in this issue.
Topics of the day:
1. "Brittle Fracture"
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Date: Fri, 13 Dec 2002 09:33:54 +0100
From: Erik de Kluizenaar <[log in to unmask]>
Subject: Re: "Brittle Fracture"
This is a multipart message in MIME format.
--=_alternative 002F346CC1256C8E_=
Content-Type: text/plain; charset="us-ascii"
Thanks for the addition Brian.
That's the hypothesis that I always use here in Philips to explain to my
collegues why nickel-gold solderability degrades to a reproducible extent
in reflow soldering, with hardly any influence of reflow peak temperature
and reflow time (five-fold reflow is still OK). Once that this fraction of
the surface area (the bottoms of the pores) have been oxidized, the oxide
patches may grow in thickness to a small extent, but the surface fraction
remains the same. This extent of the decrease in solderability is such
that a second or third soldering operation (double-sided reflow or wave
after reflow) is no major problem, be it that contact time in wave
soldering may have to be increased slightly.
NB:
Be aware of the fact that the gold of this plating has a huge
environmental impact, orders of magnitude larger than that of lead.
(Compare wire bonded ICs in which the gold bond wires with a thickness of,
say, 25 mu almost completely determine the environmental impact.) So, it
may be lead-free but it does not serve the initial goal of lowering
environmental impact at all. If you want to choose relatively
environmentally friendly finishes, think of Cu-OSP, chemical tin,
electrolytic matt tin, chemical silver and refrain from the noble metals
gold palladium and platinum.
Best regards,
Erik
---------------------------------------------------------------------------------------------------------------------------------------------
Erik E. de Kluizenaar
PHILIPS CFT - Electronic Packaging & Assembly (EP&A)
Building SAQ-p, p/o box 218, 5600 MD Eindhoven - The Netherlands
Tel/Fax: (+31 40 27) 36679/36815; E:mail [log in to unmask]
PHILIPS homepage: http://www.philips.com; PHILIPS CFT homepage:
http://www.cft.philips.com
Internal PHILIPS only:
http://pww.cft.philips.com/cfteurope/electronics/elpajo/index.htm
----------------------------------------------------------------------------------------------------------------------------------------------
Brian Ellis <[log in to unmask]>
2002-12-12 17:58
To: "(Leadfree Electronics Assembly Forum)" <[log in to unmask]>
E.E. de Kluizenaar/EHV/CFT/PHILIPS@EMEA3
cc:
Subject: Re: [LF] "Brittle Fracture"
Classification:
Erik
Good explanation. I'd like to add one more thing, if you will allow me:
nickel very rapidly forms a thin, refractive, oxide layer if exposed to
air. This is what maintains that brilliance with a slightly brownish
cast on nickel-plated parts. This is normally unsolderable, except with
halide-activated fluxes. As you have rightly pointed out, the gold is
porous and there is a little area of nickel oxide at the foot of every
pore. This myriad relatively unsolderable points also causes dewetting.
Brian
Erik de Kluizenaar wrote:
>
> Dear all,
>
> Let me try to explain some metallurgy behind the nickel-gold board
> finish (also called ENIG; terrible acronym for a chemist/metallurgist
> like myself) and the failure modes that can occur.
>
> 1. The electroless nickel plating has a built-in phosphorus content of
> about 8 mass-%. This is inherent to the replinishing type of deposition
> process and can not be avoided.
> 2. The gold flash is produced by a chemical exchange process. Nickel
> dissolves and the more noble gold ions are deposited. The thickness of
> these gold layers is typicallly 0.05 - 0.2 micrometers. This implies
> that these must be micro-porous. Otherwise, the reaction would stop at a
> layer thickness in the order of 2 to 3 nanometers.
> 3. The copper lands on which the finish is going to be applied, is
> activated with zinc, extremely finely deispersed, to provide proper
> adhesion and a fine-grained nickel microstructure.
>
> To arrive at a good quality finish, all the process steps mentioned
> above, should be well optimized and controlled. (Following the
> suppliers' process prescriptions is crucial for such processes.) If
> something goes wrong, the following imperfections may occur:
> - coarse nickel structure with irregular phosphorus distribution
> - wrong phosphorus concentration (typically more than 8 %)
> - passivation between nickel and gold (mainly determined by the rinsing
> steps)
> - poor gold deposit (too thin; too porous; uneven)
>
> Soldering with tin-based alloys, both lead-containing and lead-free,
> will produce a ralatively complex intermetallic interface, from nickel
> to solder:
> - nickel phosphide, Ni3P (thickness sub-micron and very regular)
> - nickel-tin, Ni3Sn4 (thickness typically 1-3 micrometers and very
> irregular).
> This intermetallic double layer has an intrinsic weakness against
> bending and mechanical shock loading. This is particularly pronounced
> with large and stiff components such as large BGAs. The fracture surface
> lies in the interface between these two layers and looks as an adhesive
> fracture. No brittle or ductile fracture details on either side of the
> fracture to be found using SEM. (More detail should be investigated
> using TEM and replica technology.) Microprobe analysis and
> microsectioning have further proven that this fracture mode is as
> described above.
> The colour on the nickel side is dark grey. So, this can be called
> "black pad".
> All this does not mean that such joints are bad, but any chain has a
> weakest link and with soldered joints on this type nickel-gold finish,
> this intermetallic interface is the one, particularly with incidental
> overloading such as mechanical shock.
>
> Now if the nickel quality is poor, this interface turns out to be really
> weaker in many cases. Then, the strength may be insufficient. In those
> cases, often but not always, the phosphorus content exceeds 8%. But we
> also found good quality finishes with 9% so, phosphorus is not the
> unique reliability indicator. However, processes are running out of
> control with too high P-content so, it always requires action to be
taken.
>
> The gold is micro-porous, see above. This implies that the nickel can be
> attacked through the pores if improper rinsing procedures are applied.
> This will result in the formation of corrosion products in the form of a
> passivation layer, that cannot be removed by soldering fluxes. If a
> passivation layer is present between nickel and gold, the gold will
> readily dissolve and the solder will see an unsolderable surface. On
> large solder lands this will be seen as severe dewetting and black pad,
> and on small lands the solder will be covering the lands without really
> adhering to those. So, fracture will occur at very low forces and the
> pads will also be greyish-black. This type of "black pad" is the
> dangerous one.
>
> Best regards,
> Erik
>
---------------------------------------------------------------------------------------------------------------------------------------------
> Erik E. de Kluizenaar
> PHILIPS CFT - Electronic Packaging & Assembly (EP&A)
> Building SAQ-p, p/o box 218, 5600 MD Eindhoven - The Netherlands
> Tel/Fax: (+31 40 27) 36679/36815; E:mail
[log in to unmask]
> PHILIPS homepage: http://www.philips.com; PHILIPS CFT homepage:
> http://www.cft.philips.com
> Internal PHILIPS only:
> http://pww.cft.philips.com/cfteurope/electronics/elpajo/index.htm
>
----------------------------------------------------------------------------------------------------------------------------------------------
>
>
>
>
>
>
>
>
> Dave Hillman <[log in to unmask]>
>
> Sent by:
> Leadfree <[log in to unmask]>
>
> 2002-12-11 00:09
> Please respond to "(Leadfree Electronics Assembly Forum)"; Please
> respond to ddhillma
>
>
> To: [log in to unmask]
> cc: (bcc: E.E. de Kluizenaar/EHV/CFT/PHILIPS)
> Subject: Re: [LF] "Brittle Fracture"
>
> Classification:
>
>
>
>
> Hi Bev! I have been using the following "definitions" of the two
phenomena;
> a) Black pad: a defect of immersion gold/electroless nickel (ENIG) pwb
> surface finish associated with process control issues with the ENIG
plating
> chemistry/deposition process; b) Brittle Pad: a defect of ENIG pwb
surface
> finish associated with metallurgical phase formation and elemental
> diffusion issues. This is how I have been keeping things straight
between
> Diet Coke's.
>
> Dave
>
> PS - I know you and Vladimir work in the same group -that's why I added
the
> "this is going to sound silly"... :)
>
>
>
>
>
>
> Bev Christian <[log in to unmask]>@ipc.org> on 12/10/2002 07:23:13 AM
>
> Please respond to "(Leadfree Electronics Assembly Forum)"
> <[log in to unmask]>; Please respond to Bev Christian
> <[log in to unmask]>
>
> Sent by: Leadfree <[log in to unmask]>
>
>
> To: [log in to unmask]
> cc:
>
> Subject: Re: [LF] "Brittle Fracture"
>
>
> Dave and Dave,
> We (Vladimir and myself) are being told that Black Pad and Brittle Pad
are
> DIFFERENT phenomena. Any enlightenment would be appreciated.
>
> regards,
> Bev Christian
> Research in Motion
>
> PS Vladimir works for me and we sit in the same double cubicle!
> -----Original Message-----
> From: Dave Hillman [mailto:[log in to unmask]]
> Sent: December 9, 2002 5:27 PM
> To: [log in to unmask]
> Subject: Re: [LF] "Brittle Fracture"
>
>
> Hi Vladimir! This is going to sound silly but I recommend you check with
> Bev Christian at RIM (his office should be close to yours!) - Bev should
> have the last couple of IPC Conference Proceedings which contain a
number
> of good papers on the "black pad phenomena".
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
> Vladimir Igoshev <[log in to unmask]>@ipc.org> on 12/09/2002 03:27:19 PM
>
> Please respond to "(Leadfree Electronics Assembly Forum)"
> <[log in to unmask]>; Please respond to Vladimir Igoshev
> <[log in to unmask]>
>
> Sent by: Leadfree <[log in to unmask]>
>
>
> To: [log in to unmask]
> cc:
>
> Subject: [LF] "Brittle Fracture"
>
>
> Dear All,
>
> I'm looking for any references related to so called "Brittle Fracture"
> phenomenon, which sometime can be obeserved in solder joints between BGA
> componets and ENIG finished boards.
>
> Vladimir Igoshev, Ph.D.
> Research in Motion
> Canada
>
>
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Content-Type: text/html; charset="us-ascii"
<br><font size=2 face="sans-serif">Thanks for the addition Brian.</font>
<br>
<br><font size=2 face="sans-serif">That's the hypothesis that I always use here in Philips to explain to my collegues why nickel-gold solderability degrades to a reproducible extent in reflow soldering, with hardly any influence of reflow peak temperature and reflow time (five-fold reflow is still OK). Once that this fraction of the surface area (the bottoms of the pores) have been oxidized, the oxide patches may grow in thickness to a small extent, but the surface fraction remains the same. This extent of the decrease in solderability is such that a second or third soldering operation (double-sided reflow or wave after reflow) is no major problem, be it that contact time in wave soldering may have to be increased slightly.</font>
<br>
<br><font size=2 face="sans-serif">NB:</font>
<br><font size=2 face="sans-serif">Be aware of the fact that the gold of this plating has a huge environmental impact, orders of magnitude larger than that of lead. (Compare wire bonded ICs in which the gold bond wires with a thickness of, say, 25 mu almost completely determine the environmental impact.) So, it may be lead-free but it does not serve the initial goal of lowering environmental impact at all. If you want to choose relatively environmentally friendly finishes, think of Cu-OSP, chemical tin, electrolytic matt tin, chemical silver and refrain from the noble metals gold palladium and platinum.</font>
<br>
<br><font size=2 face="sans-serif">Best regards,</font>
<br><font size=2 face="sans-serif">Erik<br>
---------------------------------------------------------------------------------------------------------------------------------------------<br>
Erik E. de Kluizenaar<br>
PHILIPS CFT - Electronic Packaging & Assembly (EP&A)<br>
Building SAQ-p, p/o box 218, 5600 MD Eindhoven - The Netherlands<br>
Tel/Fax: (+31 40 27) 36679/36815; E:mail [log in to unmask]<br>
PHILIPS homepage: http://www.philips.com; PHILIPS CFT homepage: http://www.cft.philips.com<br>
Internal PHILIPS only: http://pww.cft.philips.com/cfteurope/electronics/elpajo/index.htm<br>
----------------------------------------------------------------------------------------------------------------------------------------------</font>
<br>
<br>
<br>
<table width=100%>
<tr valign=top>
<td>
<td>
<br>
<br>
<br>
<br>
<br><font size=1 face="sans-serif"><b>Brian Ellis <[log in to unmask]></b></font>
<p><font size=1 face="sans-serif">2002-12-12 17:58</font>
<br>
<td><font size=1 face="Arial"> </font>
<br><font size=1 face="sans-serif"> To: "(Leadfree Electronics Assembly Forum)" <[log in to unmask]><br>
E.E. de Kluizenaar/EHV/CFT/PHILIPS@EMEA3</font>
<br><font size=1 face="sans-serif"> cc: </font>
<br><font size=1 face="sans-serif"> Subject: Re: [LF] "Brittle Fracture"</font>
<p><font size=1 face="sans-serif"> Classification: </font>
<br></table>
<br>
<br>
<br><font size=2 face="Courier New">Erik<br>
<br>
Good explanation. I'd like to add one more thing, if you will allow me: <br>
nickel very rapidly forms a thin, refractive, oxide layer if exposed to <br>
air. This is what maintains that brilliance with a slightly brownish <br>
cast on nickel-plated parts. This is normally unsolderable, except with <br>
halide-activated fluxes. As you have rightly pointed out, the gold is <br>
porous and there is a little area of nickel oxide at the foot of every <br>
pore. This myriad relatively unsolderable points also causes dewetting.<br>
<br>
Brian<br>
<br>
Erik de Kluizenaar wrote:<br>
> <br>
> Dear all,<br>
> <br>
> Let me try to explain some metallurgy behind the nickel-gold board <br>
> finish (also called ENIG; terrible acronym for a chemist/metallurgist <br>
> like myself) and the failure modes that can occur.<br>
> <br>
> 1. The electroless nickel plating has a built-in phosphorus content of <br>
> about 8 mass-%. This is inherent to the replinishing type of deposition <br>
> process and can not be avoided.<br>
> 2. The gold flash is produced by a chemical exchange process. Nickel <br>
> dissolves and the more noble gold ions are deposited. The thickness of <br>
> these gold layers is typicallly 0.05 - 0.2 micrometers. This implies <br>
> that these must be micro-porous. Otherwise, the reaction would stop at a <br>
> layer thickness in the order of 2 to 3 nanometers.<br>
> 3. The copper lands on which the finish is going to be applied, is <br>
> activated with zinc, extremely finely deispersed, to provide proper <br>
> adhesion and a fine-grained nickel microstructure.<br>
> <br>
> To arrive at a good quality finish, all the process steps mentioned <br>
> above, should be well optimized and controlled. (Following the <br>
> suppliers' process prescriptions is crucial for such processes.) If <br>
> something goes wrong, the following imperfections may occur:<br>
> - coarse nickel structure with irregular phosphorus distribution<br>
> - wrong phosphorus concentration (typically more than 8 %)<br>
> - passivation between nickel and gold (mainly determined by the rinsing <br>
> steps)<br>
> - poor gold deposit (too thin; too porous; uneven)<br>
> <br>
> Soldering with tin-based alloys, both lead-containing and lead-free, <br>
> will produce a ralatively complex intermetallic interface, from nickel <br>
> to solder:<br>
> - nickel phosphide, Ni3P (thickness sub-micron and very regular)<br>
> - nickel-tin, Ni3Sn4 (thickness typically 1-3 micrometers and very <br>
> irregular).<br>
> This intermetallic double layer has an intrinsic weakness against <br>
> bending and mechanical shock loading. This is particularly pronounced <br>
> with large and stiff components such as large BGAs. The fracture surface <br>
> lies in the interface between these two layers and looks as an adhesive <br>
> fracture. No brittle or ductile fracture details on either side of the <br>
> fracture to be found using SEM. (More detail should be investigated <br>
> using TEM and replica technology.) Microprobe analysis and <br>
> microsectioning have further proven that this fracture mode is as <br>
> described above.<br>
> The colour on the nickel side is dark grey. So, this can be called <br>
> "black pad".<br>
> All this does not mean that such joints are bad, but any chain has a <br>
> weakest link and with soldered joints on this type nickel-gold finish, <br>
> this intermetallic interface is the one, particularly with incidental <br>
> overloading such as mechanical shock.<br>
> <br>
> Now if the nickel quality is poor, this interface turns out to be really <br>
> weaker in many cases. Then, the strength may be insufficient. In those <br>
> cases, often but not always, the phosphorus content exceeds 8%. But we <br>
> also found good quality finishes with 9% so, phosphorus is not the <br>
> unique reliability indicator. However, processes are running out of <br>
> control with too high P-content so, it always requires action to be taken.<br>
> <br>
> The gold is micro-porous, see above. This implies that the nickel can be <br>
> attacked through the pores if improper rinsing procedures are applied. <br>
> This will result in the formation of corrosion products in the form of a <br>
> passivation layer, that cannot be removed by soldering fluxes. If a <br>
> passivation layer is present between nickel and gold, the gold will <br>
> readily dissolve and the solder will see an unsolderable surface. On <br>
> large solder lands this will be seen as severe dewetting and black pad, <br>
> and on small lands the solder will be covering the lands without really <br>
> adhering to those. So, fracture will occur at very low forces and the <br>
> pads will also be greyish-black. This type of "black pad" is the <br>
> dangerous one.<br>
> <br>
> Best regards,<br>
> Erik<br>
> ---------------------------------------------------------------------------------------------------------------------------------------------<br>
> Erik E. de Kluizenaar<br>
> PHILIPS CFT - Electronic Packaging & Assembly (EP&A)<br>
> Building SAQ-p, p/o box 218, 5600 MD Eindhoven - The Netherlands<br>
> Tel/Fax: (+31 40 27) 36679/36815; E:mail [log in to unmask]<br>
> PHILIPS homepage: http://www.philips.com; PHILIPS CFT homepage: <br>
> http://www.cft.philips.com<br>
> Internal PHILIPS only: <br>
> http://pww.cft.philips.com/cfteurope/electronics/elpajo/index.htm</font>
<br><font size=2 face="Courier New">> ---------------------------------------------------------------------------------------------------------------------------------------------- <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> Dave Hillman <[log in to unmask]><br>
> <br>
> Sent by:<br>
> Leadfree <[log in to unmask]><br>
> <br>
> 2002-12-11 00:09<br>
> Please respond to "(Leadfree Electronics Assembly Forum)"; Please <br>
> respond to ddhillma<br>
> <br>
> <br>
> To: [log in to unmask]<br>
> cc: (bcc: E.E. de Kluizenaar/EHV/CFT/PHILIPS)<br>
> Subject: Re: [LF] "Brittle Fracture"<br>
> <br>
> Classification: <br>
> <br>
> <br>
> <br>
> <br>
> Hi Bev! I have been using the following "definitions" of the two phenomena;<br>
> a) Black pad: a defect of immersion gold/electroless nickel (ENIG) pwb<br>
> surface finish associated with process control issues with the ENIG plating<br>
> chemistry/deposition process; b) Brittle Pad: a defect of ENIG pwb surface<br>
> finish associated with metallurgical phase formation and elemental<br>
> diffusion issues. This is how I have been keeping things straight between<br>
> Diet Coke's.<br>
> <br>
> Dave<br>
> <br>
> PS - I know you and Vladimir work in the same group -that's why I added the<br>
> "this is going to sound silly"... :)<br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> Bev Christian <[log in to unmask]>@ipc.org> on 12/10/2002 07:23:13 AM<br>
> <br>
> Please respond to "(Leadfree Electronics Assembly Forum)"<br>
> <[log in to unmask]>; Please respond to Bev Christian<br>
> <[log in to unmask]><br>
> <br>
> Sent by: Leadfree <[log in to unmask]><br>
> <br>
> <br>
> To: [log in to unmask]<br>
> cc:<br>
> <br>
> Subject: Re: [LF] "Brittle Fracture"<br>
> <br>
> <br>
> Dave and Dave,<br>
> We (Vladimir and myself) are being told that Black Pad and Brittle Pad are<br>
> DIFFERENT phenomena. Any enlightenment would be appreciated.<br>
> <br>
> regards,<br>
> Bev Christian<br>
> Research in Motion<br>
> <br>
> PS Vladimir works for me and we sit in the same double cubicle!<br>
> -----Original Message-----<br>
> From: Dave Hillman [mailto:[log in to unmask]]<br>
> Sent: December 9, 2002 5:27 PM<br>
> To: [log in to unmask]<br>
> Subject: Re: [LF] "Brittle Fracture"<br>
> <br>
> <br>
> Hi Vladimir! This is going to sound silly but I recommend you check with<br>
> Bev Christian at RIM (his office should be close to yours!) - Bev should<br>
> have the last couple of IPC Conference Proceedings which contain a number<br>
> of good papers on the "black pad phenomena".<br>
> <br>
> Dave Hillman<br>
> Rockwell Collins<br>
> [log in to unmask]<br>
> <br>
> <br>
> <br>
> <br>
> Vladimir Igoshev <[log in to unmask]>@ipc.org> on 12/09/2002 03:27:19 PM<br>
> <br>
> Please respond to "(Leadfree Electronics Assembly Forum)"<br>
> <[log in to unmask]>; Please respond to Vladimir Igoshev<br>
> <[log in to unmask]><br>
> <br>
> Sent by: Leadfree <[log in to unmask]><br>
> <br>
> <br>
> To: [log in to unmask]<br>
> cc:<br>
> <br>
> Subject: [LF] "Brittle Fracture"<br>
> <br>
> <br>
> Dear All,<br>
> <br>
> I'm looking for any references related to so called "Brittle Fracture"<br>
> phenomenon, which sometime can be obeserved in solder joints between BGA<br>
> componets and ENIG finished boards.<br>
> <br>
> Vladimir Igoshev, Ph.D.<br>
> Research in Motion<br>
> Canada<br>
> <br>
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End of Leadfree Digest - 12 Dec 2002 to 13 Dec 2002 (#2002-157)
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