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> Determination Of Moisture Content In Pcb, determination of moisture content in PCB
sameh
Posted: March 15, 2016 02:36 pm
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Hello
As part of my PFE to get an engineering degree, i'm dealing with PCB's in order to evaluate risks of moisture in printed circuits leading to delamination. I want to find a method to determine the MACA (maximum acceptable moisture content) in the PCB (Printed Circuit Board) as shown in the 1601 IPC standard (MACA is an estimate of the maximum amount of absorbed moisture that printed board can tolerate without damage when exposed to soldering heat and is expressed as a percentage of the dry weight of the printed board). In fact, by measuring the mass of PCBs before and after drying in the oven, when the PCB is saturated with moisture ( when it can no more gain weight), we can consider this percentage of moisture absorption the maximum one but how could we judge if that percentage is acceptable or not ? there's no standard that required a certain threshold or precise from which level we can say that the PCB isn't damaged and we should accept it !!
The moisture absorbed by the resin of the PCB is the main cause of delamination! How to know at what level of humidity, this delamination is observed?
Thank you for helping me to solve this problem
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Sch3mat1c
Posted: March 15, 2016 07:43 pm
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You'd have to perform a statistical analysis of failures, considering many different sizes and layouts of PCB. For example, a two layer board with only thin traces will outgas easily, but a thick board with many layers and many ground planes will not.

It would be a very time consuming study, but would provide the most direct evidence. The experimental design would probably be: design or obtain a representative sample of commercial boards, spanning various thicknesses, layer counts, and copper densities. Soak at high humidity for a sufficient time*, then subject the samples to an aggressive heating cycle to cause delamination. Probably an ultrasound crack detection test will be needed to verify which boards have failed, and to what degree.

*A step could be added here to identify how much soaking time is needed, for each type of board.

Perhaps there are existing articles you can reference instead.

Tim


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Hamlet
Posted: March 16, 2016 10:39 am
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Giving a quantitative description of the effects of delamination will be the key in this study.

To add to Sch3mat1cs idea of UH crack detection:

Another possibility would be to use X-ray tracing of live circuit boards. Also you could eliminate a variable or two by designing a specific test PCB layout, eg a potential divider matrix so that you could electrically and systematically address well dispersed points on the PCB. And then you could perhaps order PCB's from a selection of manufacturers, chosen by their technology.

http://www.nikonmetrology.com/en_US/Produc...nics-inspection

Here is a free and very thorough book on flex PCB's: http://flexiblecircuittechnology.com/flex4/

As Sch3mat1c said, this is a ton of work, especially given that there are very many PCB technologies (vias, adhesives and no adhesives, base material). As a thesis research, it'd make sense to limit your quest to perhaps one or two types of PCB. Single layer FR4 and maybe a double layer FR4.

PS - have you called someone at IPC? I bet a few phonecalls to them would be a fast track to concept validation and potential references to articles or the right people to call.

Cheers,
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Sch3mat1c
Posted: March 16, 2016 10:15 pm
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Speaking of alternate measurements, matrices and stuff: humidity usually affects electrical characteristics, like dielectric constant (so the capacitance between traces changes), or dielectric loss (which may require building resonators in the GHz range, and a VNA, to measure effectively).

Tim


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MacFromOK
Posted: March 16, 2016 11:32 pm
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Hmmm... I wonder if atmospheric pressure change (altitude) affects arcing to a noticeable degree?


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Sch3mat1c
Posted: March 17, 2016 01:27 pm
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We weren't talking about arcing..? But yes, look up Paschen's law.

Tim


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MacFromOK
Posted: March 17, 2016 07:51 pm
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Yeah, I know. That just popped into my head. biggrin.gif

Thanks. beer.gif


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sameh
Posted: March 24, 2016 10:54 am
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HELLO
Thank you for your help but I still could'nt find a method to calculate the MAMC sad.gif
In fact, it was written in the IPC that the MAMC in the PCB's moisture content must be between 0.1% and 0.5% compared to the resin mass and less than 0.1% compared to the total mass of PCB, i wanted to know on what basis and what's method IPC had used to determine these percentages?
haw can i please contact IPC ?

This post has been edited by sameh on March 24, 2016 10:57 am
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sameh
Posted: March 28, 2016 09:59 am
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HELLO
Please how can I contact IPC to know how they determine the MAMC !! it's so urgent please
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gremlinsa
  Posted: March 29, 2016 08:06 am
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QUOTE (sameh @ March 28, 2016 10:59 am)
HELLO
Please how can I contact IPC to know how they determine the MAMC !! it's so urgent please

ARG doh.gif ....

#1: Goto the IPC website --> http://www.ipc.org/

#2: Scroll to bottom of the page...

#3: Write down the Number next to PH..

#4: Pick up the phone...

#5: Dial the number you wrote down...

#6: TALK!!!!


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sameh
Posted: March 29, 2016 03:59 pm
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i know it's not such difficult thing but i wanted a mail to contact a responsible at IPC not the cell phone
thanks anyway
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johninmi
Posted: March 29, 2016 04:08 pm
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There is information for contacting by e-mail at that Website, too..

At the bottom of the page it's under the "Contact" link.. In the "Contact" link, there is a Menu with links for Technicals requests, as well as for other departments..

Good luck..
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