epm
Structure and Function
September 2007 Edition
Operating Manual CIG compact TMS DuplexAutomatic Soldering Machine
Page 3-17
3.6 Inert Gas System
The soldering quality of inert gas soldering machines depends first and foremost on the re-
sidual oxygen proportion. Thanks to the sophisticated design, it is possible to lower this
proportion in the epm CIG compactto an adjustable, desired PPM value.
3.6.1 Inert Gas Atmosphere
The automatic gas supply into the soldering chamber, in which the process modules are lo-
cated, prevents oxidation during the soldering process.
As compared to the normal tunnel systems, the CIG compact has a greater gas volume.
The advantage of the larger volume is that the inert gas atmosphere reacts much more
slowly to penetrating oxygen. This means that the oxygen proportion remains very constant
even with a high throughput.
3.6.2 Residual Oxygen Measurement
Constant monitoring of the residual oxygen proportion is essential for the production moni-
toring. An oxygen analyzer is mounted below the inlet tunnel for this purpose. The device is
supplied filtered gas from the soldering chamber through a measurement pipe. The value of
the residual oxygen is displayed in ppm on the PC in the MIS system.
The residual oxygen content of the inert gas atmosphere is permanently monitored and dis-
played digitally. The input target value in ppm O
2
is a maximum acceptable value. Should
this value be reached during the production, there is a malfunction, e.g. faulty gas supply,
and the machine goes into alarm mode. It is possible to specify 2 alarm values, owing to
which the valves of the gas supply are controlled.
The measurement cell of the oxygen analyzer works according to a coulometric process, in
the case of which the oxygen from the measurement gas is reduced in the electro-chemical
measurement cell. The electrolyte in the measurement cell makes it possible for the hy-
droxide ions to migrate to the anode, where they are in turn oxidized into oxygen mole-
cules. An electrode voltage of about 1.3 V DC causes reduction and oxidation as well as
the migration of the hydroxide ions.
NOTE
Always first switch off the measurement instrument before opening the soldering ma-
chine. Never replenish electrolyte, only add distilled water.
The PPM measuring instrument indicates the measured PPM value in the machine.
3.6.3 Gas
Consumption
The extremely low gas consumption values of the CIG comapct result in the inert gas at-
mosphere getting heated uniformly. This heat supports the preheating of the PCBs, so that
the soldering speed can be increased significantly without using up additional energy for
the preheating. Excellent soldering results were obtained even with a soldering speed of 2-
2.5 m/min.
However, since values with a few tens of ppm still guarantee adequate soldering values, a
lower (more cost-effective) quality of nitrogen can be used for the CIG compact.
