You can refer PCBs as MSL=3 for baking requirements.
I am working successfully with Chinese manufacturers about 20 years.
Reuven

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ב-25 באוק 2011, בשעה 15:28, Jack Olson <[log in to unmask]> כתב/ה:

> Thanks for clarifying that!
> 
> I don't know physics (I do board layout), but Werner gave presentations to
> MANY board designers using those "double" numbers, warning about the risk of
> delamination at the higher lead-free soldering temperatures.
> So in my opinion, the correct water vapor pressure is not what interests
> most people in the electronics industry. What we really want to know is how
> much effort we need to put into making sure we don't have delamination
> problems. (which I assume is related to moisture content).
> 
> Can someone just blurt out the easy answer I can memorize? (smile)
> 
> but thanks Per-Erik, that is good information
> 
> Jack
> 
> .
> On Tue, Oct 25, 2011 at 2:51 AM, Per-Erik Tegehall <
> [log in to unmask]> wrote:
> 
>> The formula used on wikipedia is for calculating the water pressure when
>> you have water vapour in *equilibrium* with liquid (bulk) water in a
>> confined volume, and that is hardly the case when a PCB is passing a
>> soldering process. ****
>> 
>> ** **
>> 
>> On the other hand, using the formula PV=nRT may also give the wrong answer
>> if n (the number of gaseous water molecules in the confined volume) is
>> assumed be unaffected when the PCB is heated. At room temperature, most of
>> the water molecules in the PCB will be bonded (adsorbed) to surfaces inside
>> the laminate. This bonded water will have other properties than bulk water.
>> Compare with an adsorbed water film on a hydrophilic surface which will form
>> at relative humidities far below 100%. When a PCB is heated, the absorbed
>> water will evaporate causing an increase of the internal pressure due both
>> to an increase of the temperature and an increase of n in the formula
>> PV=nRT. ****
>> 
>> ** **
>> 
>> The question is at what temperature will the absorbed water molecules be
>> evaporated. Due to the strong bonding of adsorbed water molecules (compared
>> to bulk water) the temperature probably needs to be considerably above 100C
>> before all water molecules have been evaporated. If we assume that all of
>> them have been evaporated at the soldering temperatures used for SnPb
>> soldering, then n would be unaffected by a further increase of the soldering
>> temperature and the formula PV=nRT could be used to calculate the increase
>> in pressure. If this assumption is wrong and there still are some water
>> molecules that have not been evaporated, an increase of soldering
>> temperature would result in a larger increase in pressure, but far from an
>> increase with 100%. Also, this means that the pressure will be far below 300
>> psi even for SnPb soldering.****
>> 
>> ** **
>> 
>> A similar question has also surfaced when discussing the effect of absorbed
>> humidity on blistering of conformal coatings. So far, I have not seen any
>> measurements or relevant calculations of what pressures could be expected
>> under these conditions. Do anyone else have knowledge of such measurements
>> or calculations?****
>> 
>> ** **
>> 
>> Per-Erik Tegehall****
>> 
>> ** **
>> 
>> ** **
>> 
>> -----Ursprungligt meddelande-----
>> Från: TechNet [mailto:[log in to unmask]] För Jack Olson
>> Skickat: den 24 oktober 2011 16:27
>> Till: [log in to unmask]
>> Ämne: Re: [TN] How do we determine the Maximum Acceptable Moisture Content
>> (MAMC) for a board?
>> 
>> ** **
>> 
>> you can check it on wikipedia...****
>> 
>> http://en.wikipedia.org/wiki/Vapour_pressure_of_water****
>> 
>> ** **
>> 
>> look at the chart, ****
>> 
>> compare the difference between 493Kelvin and 533Kelvin ** **
>> 
>> (nearly double)****
>> 
>> ** **
>> 
>> Jack****
>> 
>> **
>> 
> 
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