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Subject:
From:
Anil Kher <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 1 Sep 2005 10:56:47 +0530
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This explains it all - without shaking established science.
Thanks a lot. Prior to this I was inclined to undertake grad course again.

Anil Kher
micro interconnexion pvt. ltd
D3-12A, Corlim Industrial Estate
Corlim, Ilhas , Goa , India 403110
tel: 91-832-2284209/337. fax 2284209/2285271                             
e mail: [log in to unmask]
Leaders in Gold plated PCBs - selective/ cob
an ISO 9001-2000 Company 
 

-----Original Message-----
From: Phillip Bavaro [mailto:[log in to unmask]] 
Sent: Thursday, September 01, 2005 8:30 AM
Subject: Re: ENIG/ Immersion Gold Plating and Pre-baking & Solderability

I think I know what this discussion is missing ....someone who isn't working
to comment on it!...lol.  Anyways, I think I know what may have gone wrong
in Dave's experiment as my experiments yielded the opposite results.  I
certainly agree that baking is not going to improve the solderability on
ENIG boards, but I have never been able to discern a difference if prebaked
using this vacuum oven process.  The vacuum oven was set at 150 F to
minimize the oxidation back in the days of HASL boards and still helps on
ENIG as the gold does not seal the nickel below 100%.

This process is still being used by my former employer and survived numerous
challenges by Quality Engineers who only believed in the  220 F/24 hrs
prebake cycle.

Vacuum ovens (at least all of mine) have three ports on them, the largest
one being in back and is for the vacuum pump, and then two smaller ports
with a hose bibs on them at the front, one for room air which releases the
vacuum pressure, and the other one is for bleeding in dry nitrogen gas.

The vacuum and the heat sets the water molecules in motion, but without a
nitrogen gas stream flowing across the pwb surface, the water does not want
to leave the PWB.  Based on Bev's addition below, my assumption is that most
of the moisture is removed by the mechanical flow effects of the gas being
bled in and very little of it actually dissolves into the nitrogen.

Important also is that the dry nitrogen gas is being flow limited and
therefore trickled (bled) in to the vacuum oven chamber at a slower rate
than the pump is pulling the atmosphere out.  The pump is left on
continuously and maintains at least 24 inches of vacuum.

I started using this process many years ago for wavesoldering .125" thick
PWBs which had stored in wet conditions and exhibited huge outgassing during
wavesoldering unless vacuum baked like this.

Recently, a particularly aggresive ENIG stackup design forced me to have to
use it in order to keep extremely the high density microvia technology board
from delaminating due to the spacing of the drilled holes and the properties
of the laminates.

Besides that, it also saves 22 hours when it comes to rebaking boards before
reworking them.

Hope this is clear enough for everyone to understand.......

Phil

Bev Christian <[log in to unmask]> wrote:Paul, There is a big diference in
the scale of interest between a printed circuit board and the dimensions on
a Si wafer. I am afraid you are going to have to prove to me with data that
this could ever be an issue with a PCB.
Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Paul Edwards
Sent: August 31, 2005 1:43 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking &
Solderability


Bev,

Both N2 and H20 exists as a gas molecules in the air..
In the presence of static charging sources they can be ionized and
disassociated to form nitrogen compounds..

This can be easily seen in Si wafer cleaning processes prior to epi...

Paul

Paul Edwards
Process Engineering
[log in to unmask]
Tel: 408-433-4700
FAX: 408-433-9988
Surface Art Engineering
81Bonaventura Dr.
San Jose, CA 95134
DUNS: 944740570
CAGE/NCAGE: 1XZ48

-----Original Message-----
From: Bev Christian [mailto:[log in to unmask]]
Sent: Wednesday, August 31, 2005 10:30 AM
To: TechNet E-Mail Forum; Paul Edwards
Subject: RE: [TN] ENIG/ Immersion Gold Plating and Pre-baking &
Solderability

Paul,
Please explain to me how in the world molecular nitrogen (N2) is going to
react with water vapor in a benign environment like a near vacuum at less
than 200C. I quote from the Webelements website
http://www.webelements.com/webelements/elements/text/N/chem.html:
"Reaction of nitrogen with air
Nitrogen gas does not react with air under normal conditions.

Reaction of nitrogen with water
Nitrogen gas does not react with water. It does, however, dissolve to the
extent of about x g kg-1 at 20°C (297 K) and 1 atmosphere pressure."


We aren't not talking about lightning bolts of charge here. I would expect
the amount of charge caused by static to be relatively small, BUT I can
always be educated. :) Bev RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Paul Edwards
Sent: August 31, 2005 1:22 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking &
Solderability


Dave,

In the vacuum baking environment, the vacuum is used to lower the partial
pressure to 0 to increase the molecular diffusion of the water out of the
laminate structure..

In your experiments, the gas(N2 or Ar), serves as a thermal transfer agent
so gas filled baking would be more effective than the vacuum baking, if the
thermal energy source were heating coils...

If laminate absorbing IR sources were used instead, a vacuum bakeout would
be more effective than a "dry" gas bakeout.

Again assuming the thermal energy source is a heating coil, the ideal baking
method would be to use "bone-dry" or -100F (1ppm) or better Ar, assuming
that the moisture in the PCAs would not raise the moisture level within the
total Ar load to 0F (800ppm)...

I wouldn't use N2 because of molecular acid formation when the N2 reacts
with H20 and static electric charging sources that could occur in high air
flow environments...

Paul

Paul Edwards
Process Engineering
[log in to unmask]
Tel: 408-433-4700
FAX: 408-433-9988
Surface Art Engineering
81Bonaventura Dr.
San Jose, CA 95134
DUNS: 944740570
CAGE/NCAGE: 1XZ48

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Wednesday, August 31, 2005 7:53 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking &
Solderability

Hi Bev! Exactly! And most folks who use a vacuum bake process just kick on
the vacuum and away they go! They don't realize that the bake/vacuum recipe
they have chosen might be impeding the removal of moisture.

Dave



Bev Christian
OM>
To
Sent by: TechNet [log in to unmask]

cc


Subject
08/31/2005 09:48 Re: [TN] ENIG/ Immersion Gold AM Plating and Pre-baking &
Solderability

Please respond to
TechNet E-Mail
Forum

; Please respond
to
Bev Christian
OM>






The trick is to have the evaporation process (driving the concentration
gradient) to be slow enough to not comsume all the heat available so that
the water stays liquid.
Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Vladimir Igoshev
Sent: August 31, 2005 10:15 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking &
Solderability


Hi Dave,

That is a nice example of an adiabatic process, but it's "slightly
different" from "pumping" moisture out of a board. :-) I'm a bit surprised
with the results of your experiments. I'd expect both process to complement
each other and speed up the process: vacuuming - to maintain the
concentration gradient (driving force) and heating - to speed up diffusion
(and prevent moisture from "freezing" :-)).

Regards,

Vladimir

Vladimir Igoshev, Ph. D.
Senior 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]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of David D. Hillman
Sent: Tuesday, August 30, 2005 6:31 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking &
Solderability


Hi Richard! Just a word of caution - I did some experimenting a number of
years ago to see if either baking or vacuum baking was more effective in
removing moisture from a pwb. I expected that the vacuum baking would be the
winner but the design of experiments results demonstrated that baking was
more effective. The physical process of pulling a vacuum to remove water
ends up playing with the change of state (liquid to gas, gas to liquid, etc)
behavior which impacts the ability to remove water from the pwb. I did some
research and found a need example of pulling a vacuum on a disk of water -
the change of state from a liquid to a gas resulted in the formation of ice
(not exactly the result anyone wants to achieve)! The research illustrated
that with the right controls and a well characterized vacuum/heating recipe
you can effectively remove moisture faster than just baking but in a
practical sense, having a nitrogen or argon atmosphere with a typical baking
process was just as effective and lower cost. Any moisture baking process is
going to degrade the pwb solderability so avoiding baking if possible is the
best option.

Dave Hillman
Rockwell Collins
[log in to unmask]




"Stadem, Richard"
D-AIS.COM>
To
Sent by: TechNet [log in to unmask]

cc


Subject
08/30/2005 08:27 Re: [TN] ENIG/ Immersion Gold AM Plating and Pre-baking &
Solderability

Please respond to
TechNet E-Mail
Forum

; Please respond
to
"Stadem, Richard"
D-AIS.COM>






I do not know the answer to that, but it sounds like a good idea. I do know
that back in the 70's a major military OEM used to regularly bake pwb's at
150 F (note F, not C) at a 1/2 gravity vacuum, and they claimed the moisture
was not removed if they did not have the 1/2 gravity vacuum.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Creswick, Steven
Sent: Tuesday, August 30, 2005 8:24 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking &
Solderability

Richard,

Is it an approved/acceptable process to place the PWB's into a vacuum
chamber at room temp?

I would not hazard a guess as to how great of a vacuum for what duration,
however. Just curious if it is done in the surface mount industry.

Nothing gets any more simple than a dessicantor box though!

Steve Creswick - Gentex Corp


-----Original Message-----
From: Stadem, Richard [mailto:[log in to unmask]]
Sent: Tuesday, August 30, 2005 9:05 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG/ Immersion Gold Plating and Pre-baking &
Solderability


Baking of ENIG plated boards may be a requirement in order to drive out
moisture even though it can exacerbate a nickel oxide formation that is
already started. But there are other options for moisture removal, including
lower bake temperatures at longer times. You could even lease a precision
scale and see at what length of time is required for simply putting the PWB
into a drybox (a dessicator box such as McDry, not a nitrogen box) and
allowing it to dry at room temperature for a period long enough to reduce
the moisture content by 90% or more. J-STD-030 does state that the bake
times and temperatures they list for components and pwbs are guidelines. If
you can prove your bake process or dessication process is removing the
moisture, then you are qualifying a lower temp and longer time. You will
need to use a number of pwbs in order to do this, as there is some variation
in weights caused by resin content, etc. But you should be able to show a
reduction in the average of weights (mean weight).

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Schaefer
Sent: Friday, August 26, 2005 10:10 AM
To: [log in to unmask]
Subject: [TN] ENIG/ Immersion Gold Plating and Pre-baking & Solderability

Does baking these types of plating affect solderability? If so what factors
play a part (i.e. baking temperature, plating thickness, baking time,
etc...). I know that if baked it can cause the Nickel Oxide layer to become
less solderable if the plating process is Poor (thanks Richard S.). Is there
is a factual study that proves that baking any type of gold plated boards in
any way shape or form reduces the solderability and/ or reliablity of the
joints/ product? I am trying to gather data to prove to management that
baking is a bad decision with this type of plating and should never be
performed. Also if a Gold Plated board of any type is suspect for high level
moisture content - how do you remove the moisture "IF" baking is not
acceptable?


Chris Schaefer
Suntron Corporation

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