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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 25 Oct 2011 13:08:06 -0500
Content-Type:
text/plain
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text/plain (676 lines)
I agree. This looks like one of those Chinese PWB fabricators your Uncle Dean warned you about.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ian Hanna
Sent: Tuesday, October 25, 2011 11:53 AM
To: [log in to unmask]
Subject: Re: [TN] How do we determine the Maximum Acceptable Moisture Content (MAMC) for a board?

looks like it`s a pcb for a `waterproof mp3`not a waterproof pcb -- in usa
they make pcbs for space application - but these also are sub-assemblies
and do not fly on their own...





From:
Inge Hernefjord <[log in to unmask]>
To:
<[log in to unmask]>
Date:
25/10/2011 11:42 AM
Subject:
Re: [TN] How do we determine the Maximum Acceptable Moisture Content
(MAMC) for a board?
Sent by:
TechNet <[log in to unmask]>



Richard,
if you want waterproof boards, buy from.....China...I hesitated to use the
name..was afraid you would throw up..( chuckle)

http://www.alibaba.com/product-gs/423958616/waterproof_mp3_bare_pcb.html

If this was true, we would have seen a veritable success.
I think it's about misusing the word 'waterproof' , or at least different
opinions about what waterproof means.

Inge




On 25 October 2011 15:08, Stadem, Richard D. <[log in to unmask]> wrote:

> Hi, Inge.
> Delamination and measling still occur, but much more infrequently. I
> believe this is simply due to a much more robust pre-preg quality in the
> market. However, delamination does occur more frequently with polyimide
> slash types. You just gotta pre-bake or you will eventually have issues.
>
> And don't try to save money by buying PWBs from China. You will get
burned-
> big time. I have been getting calls quite frequently in the past year to
> look at various lots of PWBs manufactured in China with all kinds of
quality
> issues. Problem is, some of the more reliable PWB companies have
attempted
> to form offshore partnerships in an effort to reduce costs and become
more
> competitive, but did not do their homework when selecting an offshore
> supplier, and did not place a company rep at the site. PWB suppliers
never
> voluntarily reveal to their customer that they are buying offshore.
> Invariably, poor workmanship and/or poor materials slip through and are
not
> detected until during manufacturing or after.
>
> I am not saying all Chinese or all offshore PWB fabricators are of poor
> quality, I am simply stating that there are a lot of companies out there
> that make crap, and you have to be very careful of your PWB's pedigree.
>
> Waterproof PWBs? I would need a lot of data to believe that claim.
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
> Sent: Monday, October 24, 2011 4:43 PM
> To: [log in to unmask]
> Subject: Re: [TN] How do we determine the Maximum Acceptable Moisture
> Content (MAMC) for a board?
>
> I forgot a question I had to you all:  how frequent is delamination
(caused
> by water vapour) nowadays. It's a long time since I heard of serious
> problems. Perhaps one or two cases with a single board or two, but in a
> mass
> production that would not be count as an issue.
>
> IF delamination is much lower today, what is then the reason, and is the
> improvement global or significant for a limited number of suppliers? And
> also this (perhaps stupid) question: Has anyone seen boards marked
> 'waterproof' . I read somewhere about such boards and my guess is that
the
> boards were coated. But waterproof? Hmmm..
>
> Inge
>
>
>
>                              -------------------------
>
> Hi all,
>
> I think many industries make their decisions based on empirical data and
> own
> experience.
> My own opinion is, and few will agree, that the whole idea of a
> standardized
> humidity level is disputable, because the humdity is not constant from x
to
> y, nor from Z 1 to Z2. Furthermore, the humidity is varying with time
and
> temperature, sometimes within seconds. Moreover we have the board's
surface
> condition, percentage of copper,  access to mobile ions and a lot more.
> Which was pointed at by Dave
> Hillman.
>
> It all starts with the ability of water condensation on the surface
> followed
> by the rate of penetration of gas and water vapor into the board
structure.
> The water content on the very surface is not included in the discussion,
> because it's not relevant for the soldering process. It's the inside
> accumulation of water that is the input for the standard.
>
> To get knowledge of the water content, you 'simply' perform a weight
> control
> of the board, starting with boards that have been in a humid atmosphere,
> e.g. from stock or from a humidity test. Then you bake out the water and
do
> a weight control again. The diff is the water content.
>
> Here starts the questions and the aquestionings. The bakeout is the
first
> problem, because you don't know how effective this process is. The
actual
> standard says, that we hope that at least 90 % of the water will find
its
> way out and disappear. But who knows. It's a question of the leakage of
> water molecules through millions of micron sized pores in the epoxy
> structure. And the one who has learned about the percolation of
molecules
> know that this is very complicated a thing. furthermore we have the
> diffusion of water vapor through the same micron sized 'orifices', also
a
> far from easy to understand process. Depending on the charachter of
these
> labyrints, we have a variation of water escaping rate. Compare with the
> water on the surface. Water molecules can stick to the outermost
crystals
> as
> billions of droplets, or cover the entire surface as one and a single
one
> water layer. The evaporation of water can vary a lot. Imagine what
happens
> when you clean your glasses. You breathe on them, water condensates in
less
> than  seconds, and you have some more seconds to rapidly wipe the glass
> with
> a tissue. If you are late, you'll see how the water leaves rapidly.  If
you
> do the same on a sheet of plastic, the water film can stay for minutes.
> Likewise, the transportation of water from the inner regions of a PWB
can
> vary a lot, depending on what base material is used, number of copper
> layers, reinforcement materials etc. Some water can be so bound to the
> structure by the capillary force, that it's nearly impossible to get rid
of
> it. There is a lot more to say, but I stop here (to the relief of many).
>
>
>
> Now, what about the small activity with small resources for analysis and
> advanced incoming inspection? They have no idea about the water content
> Perhaps a passus in the purchase  handling. Yes, it's one way. Another
way
> is to look back and see how their products behave in a long term. A
further
> way is to avoid long storage before soldering. Perhaps they have someone
> who
> knows a little about nature's behaviour, i.e. the ambition to get a
state
> of
> equilibrium. If you have 50% RH in a room and put a PWB on the desk,
> humidity will increase in the board until there is an equality on inside
> vs.
> outside. How fast?   It depends on how many PTHs you have, o how many
vias
> and how  the edges of the board are humidity inlets.  One way to get an
> idea
> is to create buried capacitors in the PWB, expose the board to humidity
and
> measure the capacitance change vs. time.  You'd be surprised how fast
> humitity gets on inside of a board. Halfways to quilibrium can occur
from
> 10
> hs to 100 hs. So, a board that has been lying for weeks in a humid
store,
> may hold  such a lot of water, that you are far from 0.1 wt% after
bakeout.
> You may have 0.5 wt%, 1 wt% or more. Without knowing. Tests on a variety
of
> boards gives that equilibrium is obtain after as short a time as a few
> hours
> to as long long a time as one year!
>
>
> So, that's why I wonder with what confidence we follow the 0.2 % rule.
With
> all respect to those who work with the IPC norms. Am not against, nor
pro.
>
> End of old man's gagging
>
> Inge
>
> PS, If you don't have Chris Hunt's splendid report (he is a TN member),
I
> got it. Title: Moisture Measurements in PCBs and Impact of Design on
> Desorption Behaviour.  Not a paper with pages and pages with maths that
you
> don't understand, but a language and with  illustrations that explains
> complicated things so even a gaga like me can melt.
>
> Inge
>
>
> - Show quoted text -
> On 23 October 2011 00:03, David D. Hillman
<[log in to unmask]>
> wrote:
>
> Hi Rigo - yes, Doug would give you the standard " it depends" response
> because as you detailed,there are too many inputs to your question. The
> reason that the IPC-1601 committee only put suggested values in the
> standard is that clear, data determined, industry wide applicable values
> for requirements could not be established. The committee is continuing
to
> investigate, research and gather published data on that task.
Establishing
> industry wide applicable values is a difficult task as the committee
does
> not want to impose any requirements that are not based on data and are
not
> value added for the industry.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
>
> "Garcia, Rigo (GSFC-300.0)[MANTECH SRS TECHNOLOGIES]"
>
> <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 10/21/2011 01:31 PM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
>
> "Garcia, Rigo (GSFC-300.0)[MANTECH SRS TECHNOLOGIES]"
>
> <[log in to unmask]>
>
>
> To
> <[log in to unmask]>
> cc
>
> Subject
> [TN] How do we determine the Maximum Acceptable Moisture Content (MAMC)
>
> for a board?
>
>
>
>
>
>
> Hi everybody,
>
> Does anybody know how do we determine the Maximum Acceptable Moisture
> Content (MAMC) for a board?
>
> I understand that IPC-1601 states that for most designs a MAMC between
> 0.1% and 0.5% of moisture weight to resin weight is adequate. However,
it
> does not describe the basis to establish the range. I can think of many
> variables that can affect this number like minimum pitch, voltage
across,
> component clearance, whether the board gets conformal coating or not,
etc.
> I would like to know if anybody knows of a safe method to determine the
> MAMC for a given board.
>
> Paul... I can already see your "it depends" coming... :)!
>
> Thanks for the help!
>
> Rigo Garcia
>
> Sr. Quality Assurance Engineer
> Workmanship Standards, Code 300
> NASA, Goddard Space Flight Center
> Greenbelt, MD  20771
> Phone. (301) 286-6129
> Fax.       (301) 286-6576
>
>
> ______________________________________________________________________
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>
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> -----------------------------------------------------
>
> On 23 October 2011 07:31, Reuven Rokah <[log in to unmask]> wrote:
>
> > Hi Bev,
> > You can check the graph for vapor pressure (psi) vs temp. of Werner's
> white
> > paper for PCBs.
> > I believe this graph is based on experimental measurements. I assume
that
> > there are more factors (than the PV formula) influencing the vapor
> pressure
> > inside the PCB layers during reflow.
> > Reuven
> >
> > On Sun, Oct 23, 2011 at 3:48 PM, Bev Christian
> > <[log in to unmask]>wrote:
> >
> > > Reuven,
> > > I respectfully disagree.  Even if we assume a peak reflow
temperature
> for
> > > eutectic tin/lead solder of only 205C and a high 260C for SAC305 the
> > vapor
> > > pressure due to trapped air and/or moisture is still not going to
> double.
> > >
> > > P1V1=n1RT1
> > > P2V2=n2RT2
> > >
> > > R = a constant
> > > n1 = n2
> > > V1 = V2
> > >
> > > Leaving
> > > P1/P2 = T1/T2
> > >
> > > 300/P2 = (205+273)/260+273)
> > >
> > > P2 = 300*533/478
> > >
> > > P2 = 334  That is only an 11% increase.
> > >
> > > Not sure where the 300 came from in the first place, but no matter
what
> > > number you start with, it does not double.
> > >
> > > Bev
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask]] On Behalf Of Reuven Rokah
> > > Sent: Sunday, October 23, 2011 5:03 AM
> > > To: [log in to unmask]
> > > Subject: Re: [TN] How do we determine the Maximum Acceptable
Moisture
> > > Content (MAMC) for a board?
> > >
> > > Hi Garcia,
> > > You didn't mention the most important variable: the process
technology,
> > the
> > > vapor pressure (300 to 650 psi) of Lead free is more than double
than
> > > Leaded
> > > process at the reflow peak temp.
> > > the MAMC for Leaded process should be 0.20% and for Lead Free 0.17%.
> > (ref.
> > > Werner Engelmaier PCB FAB Notes).
> > > Reuven
> > >
> > > On Fri, Oct 21, 2011 at 8:31 PM, Garcia, Rigo (GSFC-300.0)[MANTECH
SRS
> > > TECHNOLOGIES] <[log in to unmask]> wrote:
> > >
> > > > Hi everybody,
> > > >
> > > > Does anybody know how do we determine the Maximum Acceptable
Moisture
> > > > Content (MAMC) for a board?
> > > >
> > > > I understand that IPC-1601 states that for most designs a MAMC
> between
> > > 0.1%
> > > > and 0.5% of moisture weight to resin weight is adequate. However,
it
> > does
> > > > not describe the basis to establish the range. I can think of many
> > > variables
> > > > that can affect this number like minimum pitch, voltage across,
> > component
> > > > clearance, whether the board gets conformal coating or not, etc. I
> > would
> > > > like to know if anybody knows of a safe method to determine the
MAMC
> > for
> > > a
> > > > given board.
> > > >
> > > > Paul... I can already see your "it depends" coming... :)!
> > > >
> > > > Thanks for the help!
> > > >
> > > > Rigo Garcia
> > > >
> > > > Sr. Quality Assurance Engineer
> > > > Workmanship Standards, Code 300
> > > > NASA, Goddard Space Flight Center
> > > > Greenbelt, MD  20771
> > > > Phone. (301) 286-6129
> > > > Fax.       (301) 286-6576
> > > >
> > > >
> > > >
> ______________________________________________________________________
> > > > This email has been scanned by the MessageLabs Email Security
System.
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> > > [log in to unmask]
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> ______________________________________________________________________
> > > >
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> > > > -----------------------------------------------------
> > > >
> > >
> > >
> > >
> > > --
> > >
> > > Best Regards,
> > >
> > > *Reuven Rokah*
> > >
> > > Mobile: 972-52-60-120-18
> > > Tele-fax: 97239360688
> > > <http://www.rokah-technologies.com/>[log in to unmask]
> > > [log in to unmask]
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> > >
> > > **
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Rokah
> > > Technologies. If you have received this transmission in error,
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> > > files
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> > >
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> > >
> >
> >
> > --
> >
> > Best Regards,
> >
> > *Reuven Rokah*
> >
> > Mobile: 972-52-60-120-18
> > Tele-fax: 97239360688
> > <http://www.rokah-technologies.com/>[log in to unmask]
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