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H.P.

#13156

N2 Reduction | 29 December, 1998

Does anyone have angles on how to reduce N2 consumption at reflow process (i.e. process control equipment, etc.)?

Any help would be appreciated

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Earl Moon

#13157

Re: N2 Reduction | 29 December, 1998

| Does anyone have angles on how to reduce N2 consumption at reflow process (i.e. process control equipment, etc.)? | | Any help would be appreciated | N2 consumption is very "machine" and process dependent. Some machine designs are better equipped to be more efficient. Often more efficient machines have very carefully thought out methods and mechanisms to minimize consumption. Examples include dams or buffers at inlets and outlets restricting O2 interference and N2 loss. Others include oxygen reduction systems that "suck" out the unwanted gasses and stabilize inert gas use and blanketing in reflow or wave soldering areas requiring an inert atmosphere (fluxing and reflow zones as examples).

Machines having been retrofitted often do not take into consideration maximizing N2 use efficiency. Some machines with "built in" inert gas capabilities often have not been designed as well as possible.

There still exists a learning curve for some machine manufacturers (as part of the rush to get to market) required to promote efficient gas use. Some have been at it longer than others. There are several current examples of a reasonably efficient machine types available today. Plus, there are ways to get older machine types to perform better.

In advance of evolutionary design improvement, you may experiment with loss reduction and efficiency. There are many ways to approach the issue. Contact me off forum for more information concerning the methods required to effect efficiency and effectivenes of inert gas soldering capabilities.

Earl Moon

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Marc P.

#13158

Re: N2 Reduction | 30 December, 1998

| Does anyone have angles on how to reduce N2 consumption at reflow process (i.e. process control equipment, etc.)? | | Any help would be appreciated | There are a number of ways to reduce consumption:

1)One way to look at consumption is to view it as "loss". Nitrogen is lost up the exhaust stack and at the entrance and exit openings of the oven. Since there are minimum exhaust requirements, not much of a change can be effected through exhaust.

However, reducing the opening size of the entrance and exit will help. The opening size can be reduced by simply closing off any tunnel space that is not occupied by the PCB. Come down from above the PCB, up from below and in from both sides to create a "slit" for the PCB to pass through.

We have seen some users even tape cardboard onto the ends of the oven tunnel to accomplish this. While this is primitive at best, it will allow you to quickly quantify the effect. Then you can develop some more suitable tooling later.

2)An easy way to reduce consumption is to increase the oxygen PPM level in the oven. This is quite simple and typically does not have a detrimental effect on the solder results. We have seen many large OEM's running at as much as 500-1000 PPM of O2. Depending upon your current PPM levels, you may see as much as 10-25% reduction in consumption.

3)Closed loop controls--There is a Danish company "PBI Dansensor" that makes a closed loop controller. (I do not work for Dansensor so this is not a plug) With the closed loop system, you set the PPM level you want and the unit will open and close the nirogen inlet valve as required to maintain the desired level.

This approach dovetails with #2 above but provides a bit more accuracy and consistency in control as it compensates for heavy or light board loads and ensures consistent results.

4)Remove the mesh belt from your oven--If you are running exclusively on the edge hold conveyor, you can remove the mesh belt without impacting the functionality of the oven. However, by getting the mesh belt out of the way, you can further reduce the tunnel opening size and bring your tooling up very close to the bottom side of the PCB.

Clearly there are other methods employed by oven mfrs when they are building the oven. I would suggest you push the vendor of your oven to see what if any of these methods can be field retrofitted to your system

Hope this helps,

Marc

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