TECHNET Archives

October 2011

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Phil Bavaro <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 25 Oct 2011 11:10:44 -0700
Content-Type:
text/plain
Parts/Attachments:
text/plain (646 lines)
Dean Richard (sounds about right!),

Did you by any chance help author IPC-1601?  It has a familiar ring to
it.....

I have asked my admin to buy a copy the document as I have been having
some issues with sleepwalking lately.  I learned a new word today.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, October 25, 2011 10:38 AM
To: [log in to unmask]
Subject: Re: [TN] How do we determine the Maximum Acceptable Moisture
Content (MAMC) for a board?

Sorry, Patrick, but that will not work. Did you mean 100 deg. C?

For all of you with questions about baking, storage, handling, and
packaging of PWBs and CCAs, please read IPC-1601. It is an excellent
source of information on:
How to determine the RATE of moisture ingression for any PWB or CCA, as
well as various slash sheet materials.
How to condition a PWB or CCA to achieve its maximum saturated moisture
content (no, it cannot be done by immersion in water).
How to determine its RATE of moisture removal (the rate is important,
not the initial weight or final weight).
How to determine the OPTIMUM bake time and temperature for any given PWB
or CCA (customized for yours!).
How to RETAIN the level of dryness considered safe for reflow,
wave/selective soldering, and hand soldering.
Why a vacuum bake does little to help reduce the bake temperature/time,
and in fact may even damage the PWB/CCA beyond repair (especially if you
leave the vacuum in place and remove the heat).
Why a desiccator such as a McDry or Dr. Storage cabinet is a useful
(although not necessarily required) piece of equipment and should be
present in every assembly and fabrication house.
Why bake temperatures should not exceed 105 deg. C.

And a multitude of other useful tidbits of information. Get it today at
www.ipc.org while supplies last! Can't sleep at night? What better way
of achieving somnambulistic bliss could there be? Can you think of a
drier subject? The cost of this document is cheaper than any
over-the-counter sleep aid or any other method. Well, except maybe some
great...never mind, can't talk about that here.

dean


-----Original Message-----
From: Goodyear, Patrick [mailto:[log in to unmask]]
Sent: Tuesday, October 25, 2011 10:58 AM
To: 'TechNet E-Mail Forum'; Stadem, Richard D.
Subject: RE: [TN] How do we determine the Maximum Acceptable Moisture
Content (MAMC) for a board?

All,

While we don't make circuit boards we do do a lot of repair on vintage
circuit boards.  We are located on the Pacific coast RH runs around 80%
or higher.  We have a huge issue with measling on boards when we rework.
If we have time we put them in an oven at 150 deg for a day or so to dry
them out, when we can't we use a heat gun to raise a localized area to a
higher temperature to drive off the moisture, this works fairly well,
but issues still prevail.

One could put the boards in a vacuum chamber at a higher temp say 100
deg F. something similar to an autoclave to dry the boards, I suppose
they could then be sealed with a moisture barrier, vacuum vapor
impregnated, hmmm it might work.

Pat

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, October 25, 2011 6:08 AM
To: [log in to unmask]
Subject: Re: [TN] How do we determine the Maximum Acceptable Moisture
Content (MAMC) for a board?

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


______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask]
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives For additional information, or contact
Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------



______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask]
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0 To
unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives For additional information, or contact
Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

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.
> > > For more information please contact helpdesk at x2960 or
> > [log in to unmask]
> > > __________________________________________________________________
> > > ____
> > >
> > > ---------------------------------------------------
> > > Technet Mail List provided as a service by IPC using LISTSERV 16.0
> > > To unsubscribe, send a message to [log in to unmask] with following
> > > text
> > in
> > > the BODY (NOT the subject field): SIGNOFF Technet To temporarily
> > > halt or (re-start) delivery of Technet send e-mail to
> > > [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE
> > > mailing per day of all the posts: send e-mail to
> > > [log in to unmask]: SET Technet Digest Search the archives of
> > > previous posts at:
> > http://listserv.ipc.org/archives
> > > For additional information, or contact Keach Sasamori at
> [log in to unmask]
> > > 847-615-7100 ext.2815
> > > -----------------------------------------------------
> > >
> >
> >
> >
> > --
> >
> > 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]
> > www.rokah-technologies.com
> >
> > **
> > This e-mail message is intended for the recipient only and contains
> > information which is CONFIDENTIAL and which may be proprietary of
> > Rokah Technologies. If you have received this transmission in error,
> > please inform me by e-mail, phone or fax, and then please delete all
> > of the original files and all other copies exist.
> >
> >
> >
______________________________________________________________________
> > This email has been scanned by the MessageLabs Email Security
System.
> > For more information please contact helpdesk at x2960 or
> [log in to unmask]
> >
______________________________________________________________________
> >
> > ---------------------------------------------------
> > Technet Mail List provided as a service by IPC using LISTSERV 16.0
> > To unsubscribe, send a message to [log in to unmask] with following
text
> in
> > the BODY (NOT the subject field): SIGNOFF Technet
> > To temporarily halt or (re-start) delivery of Technet send e-mail to
> > [log in to unmask]: SET Technet NOMAIL or (MAIL)
> > To receive ONE mailing per day of all the posts: send e-mail to
> > [log in to unmask]: SET Technet Digest
> > Search the archives of previous posts at:
> http://listserv.ipc.org/archives
> > For additional information, or contact Keach Sasamori at
[log in to unmask]
> > 847-615-7100 ext.2815
> > -----------------------------------------------------
> >
> >
>
>
> --
>
> 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]
> www.rokah-technologies.com
>
> **
> This e-mail message is intended for the recipient only and contains
> information which is CONFIDENTIAL and which may be proprietary of
Rokah
> Technologies. If you have received this transmission in error, please
> inform
> me by e-mail, phone or fax, and then please delete all of the original
> files
> and all other copies exist.
>
>
> ______________________________________________________________________
> This email has been scanned by the MessageLabs Email Security System.
> For more information please contact helpdesk at x2960 or
[log in to unmask]
> ______________________________________________________________________
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 16.0
> To unsubscribe, send a message to [log in to unmask] with following text
in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to
> [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to
> [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at:
http://listserv.ipc.org/archives
> For additional information, or contact Keach Sasamori at
[log in to unmask] or
> 847-615-7100 ext.2815
> -----------------------------------------------------
>


______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask]
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
To unsubscribe, send a message to [log in to unmask] with following text
in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
For additional information, or contact Keach Sasamori at [log in to unmask]
or 847-615-7100 ext.2815
-----------------------------------------------------

______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask]
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
To unsubscribe, send a message to [log in to unmask] with following text
in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
For additional information, or contact Keach Sasamori at [log in to unmask]
or 847-615-7100 ext.2815
-----------------------------------------------------

______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or
[log in to unmask] 
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
To unsubscribe, send a message to [log in to unmask] with following text
in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search the archives of previous posts at:
http://listserv.ipc.org/archives
For additional information, or contact Keach Sasamori at [log in to unmask]
or 847-615-7100 ext.2815
-----------------------------------------------------

------------------------------------------------------------------------------
This message and any attachments are solely for the use of the addressee and may contain L-3 proprietary information that may also be defined as USG export controlled technical data. If you are not the intended recipient, any disclosure, use or distribution of its content is prohibited. Please notify the sender by reply e-mail and immediately delete this message and any attachments.




______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2