Hello again Brian,

No offense intended on my last posting.  I was saying the waste of
resources etc in a very tongue-in-cheek manner and that is something "we"
do not do.  However, I was in no way trying to say you wasted resources nor
generally anything negative about your company - I mistook our beggining
discussion as light banter - so I apologize if I offended you.

Anyway, starting afresh from a process discussion view point, I don't
understand why the internal dimensions of the reflow unit would affect the
N2 consumption rate.  For instance say that  assuming a sealed unit (i.e.
an ideal sealed box) with two openings and a constant flow rate.  The
consumption rate of gas exiting should be a direct function of the total
opening size, the internal absolute pressure and the external absolute
pressure.  Or more simply, the opening size in "the box" and the relative
internal pressure.  Once the ideal box is at steady state with a constant
flow rate, the consumption should be the same regardless of the internal
cavity volume.

However, the size of the internal cavity volume will have an effect on the
residual oxygen content when it relates to re-circualtion etc.  Which comes
back to Paul's equation - which BTW Paul is very good- thanks for the
input.  Well Brian, let me know what you think on this position and I am
actually glad to have a discussion about the mechanics of the reflow
process - this topic does not get discussed very often on technet.  Take
care...

Doug Bennett
Sales Engineer
Heraeus Amersil, Inc.


At 01:49 PM 4/30/98 -0400, you wrote:
>Also reflow oven/ wave solders do not consume nitrogen, they only use
>the material for atmosphere.  Any only waste is the energy to generate
>the nitrogen.
>
>>>> ETS <[log in to unmask]> 04/30/98 11:58am >>>
>Doug,
>
>Pretty cheap shot there. What are you trying to say, that I and my
>company
>promote waste of our natural resources. If I were you I would not make
>any
>claims that I cannot support with facts.
>
>I would also like to challenge your statement of your reflow using one
>half
>to one third of the N2 that our reflow systems (or any others for that
>matter) use. I am sure that the people on this forum would like to see
>who
>has the lowest N2 consumption. In addition you should mention how
>wide, long
>and tall your process cavity is as that makes a big difference. At ETS we
>compare N2 consumption to throughput.
>
>Brian
>
>>Hello again Brian,
>>
>>In my immediate defense I have to say that not only do we discourage
>the
>>wanton waste of natural and national resources by using too much
>Nitrogen
>>but also we offer a Reflow System that uses one-half to one-third of
>the
>>consumption rate of any oven I have seen on the market.  Ok, ok, I'll
>stop
>>with the tongue-in-cheek adverts =-)
>>
>>On to the technical issues, I would say that the effect will not be quite a
>>linear relationship but it should be pretty close.  At the same flow rate
>>and all variables being constant (bar the additional oxygen molecules) I
>>would not see you having any problem getting under 50 ppm with a 25 -
>30
>>ppm source - if that is indeed what they are able to get (I suggest
>making
>>sure they are correct about their numbers).  So, unless someone
>disagrees,
>>I do not think the expansion rate differentail between N2 and O2 will be
>>significant.  If you find out otherwise please let me know.  I may not be
>>telling you anything new, but there's my two-cents.  Take care.
>>
>>Doug Bennett
>>Sales Engineer
>>Heraeus Amersil, Inc
>>Atlanta, Georgia, USA
>>770-623-5630 ext 4225
>>
>>
>>
>>At 03:39 PM 4/29/98 -0700, you wrote:
>>>Doug,
>>>
>>>I appreciate your input but it does not really answer my question. I am
>>>aware that by putting high amounts of N2 in the machine the customer
>can
>>>reach the same PPM level as the source Nitrogen but no customer in
>their
>>>right mind is going to want to pay for that. You may ask your
>customers to
>>>do that but we look for affordable N2 processing methods for our
>customers.
>>>Sorry, had to put at least one plug for my company just to return the
>favor!
>>>;-)
>>>
>>>The real question is at the same flow rates how will the purity levels in
>>>the process cavity be affected if the source is 25 - 30 ppm. Keep in
>mind
>>>that ETS ovens run at approx 9 ppm throughout the process cavity
>when the
>>>source is less than 5 ppm (approximately 2-3 ppm). Should the
>customer be
>>>able to acheive less than 50 ppm (in other words add the inpurities in
>the
>>>source to the PPM levels acheived in ETS Factory or does the
>expansion rate
>>>of O2 affect this number)?
>>>
>>>I appreciate any advise offered.
>>>
>>>Brian
>>>
>>>
>>>
>>>
>>>>Hi Brian,
>>>>
>>>>To answer your question they will be able to reach whatever
>>>>purity level their gas is spec'ed at as long as they are willing to pay
>for
>>>>it in total nitrogen consumption.
>>>>
>>>>Simply put, the spec residual oxygen level will be dependent on the
>>>>internal (relative) positive pressure of the gas inside the process
>>>>chamber.  Specific formulas for consumption depend on oven design
>so it is
>>>>best to use empirical data - i.e. run experiments.  But if they crank up
>>>>the internal pressure they will be able to reach those levels but they
>will
>>>>have to pay for it, and prices of Nitrogen in Asia are quite expensive.
>>>>
>>>>On another note, your customer will also have fluctuating levels of
>>>>residual oxygen along the length (and width for that matter) of the
>process
>>>>chamber.  This situation depends on your configuration for feeding
>nitrogen
>>>>into the process chamber.  So, if your customer has concerns about
>>>>reliability of a steady residual oxygen level throughout the entire
>process
>>>>chamber this could be a problem.
>>>>
>>>>Hope this helps
>>>>
>>>>Doug Bennett
>>>>Sales Engineer
>>>>Heraeus Amersil, Inc.
>>>>Atlanta, Georgia
>>>>770-623-5630 ext 4225
>>>>
>>>>
>>>>At 04:48 PM 4/27/98 -0700, you wrote:
>>>>>Dear Technet,
>>>>>
>>>>>My company builds reflow ovens that are capable of processing in
>a Nitrogen
>>>>>(N2) atmosphere. We are getting ready to send an N2 machine to a
>>customer in
>>>>>Asia. While preparing for the installation our customer found that his
>>>>>source N2 has 25 - 30 PPM of Oxygen (O2). At our factory we
>have source N2
>>>>>that is 99.999% pure or has 1-3 PPM of O2. With this source purity
>level we
>>>>>are able to acheive less than 20 PPM of O2 in the process cavity.
>With this
>>>>>in mind what purity level should our Asian customer be able to
>acheive with
>>>>>his source of 25 - 30 PPM?
>>>>>
>>>>>Is there a relationship between source N2 and process cavity purity
>levels
>>>>>at constant flow rates? Does it have something to do with the
>expansion
>>>>>rates of these gases during heating?
>>>>>
>>>>>Thanks in advance for all replies.
>>>>>
>>>>>Brian Stumm
>>>>>
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