Vacuum hold down

The probe station should have some means for holding down the device under test. A common approach is to use vacuum hold down, but many probe stations have platens with vacuum ports spaced to hold down whole wafers rather than diced parts. It is possible to block some of the outlying vacuum ports with tape so that sufficient vacuum can be developed in the inner vacuum ports to hold down the die. Alternatively, the die can be held in place with double-sided sticky tape, but this tape can leave a residue on the probe station platen and the back of the part under test. 

Pre-polymer of PDMS was cured with holding down the edges of the slightly oversized Mylar backing film using vacuum plate at 67 °C on hotplate for 18 h. Thicker plates were fabricated as follows. To ensure the PDMS stamp were absolutely flat and uniform, two PDMS pre-polymer mixture (1 5) layers were coated and put in contact via lamination. Thus, a 25 pm thick layer of PDMS pre-polymer was directly coated on the PR master surface and another 25 pm thick layer was coated on to the stamp s Mylar backing (Fig. 10.27a, b). The two pre-polymer layers were then laminated before the curing step. 

Fig. 10.29. Distortion measurements collected at 36 points equally spaced across a 12-inch x 12-inch stamp supported by a 250 pm thick Mylar backing. In this case a vacuum plate was used to hold down the Mylar backing on the glass master during the composite stamp curing step (67 °C on a hot plate for 18 h). (a) The top frame shows a vector diagram...

A standard test method for RGA is Method 1018.4 of MIL-STD-883F according to which mass spectrometry is used to detect moisture and other volatilized compounds present in sealed microcircuit packages. The sealed modules are first preconditioned to remove external contaminants and adsorbed moisture by prebaking for 16-24 hours at 100 5 °C then placed in a vacuum holding chamber that is attached to the spectrometer. The device and chamber are then pumped down and stabilized at 100 5 °C, after which the lid of the device package is punctured and internal gas from the package allowed to enter the mass spectrometer. 

Here the mechanical properties are not so important because the external windows are not subjected to big temperature variations, and they do not need to be clamped down hard because the vacuum inside the cryostat holds them in place. 

Many phases of an autoclave cycle may be controlled through pressure signals. Pumping down to preliminary vacuums continues until pressure signals isolate the pump and open a steam valve. The sterilization hold phase may also be controlled by pressure signals. The pressure at which the specified temperature was reached may be maintained within limits of pressure (and hence of tern-... 

Favourable features of empty columns are that they give a low hold-up and a small pressure drop, so that their main applications are in the fields of micro-distillation (section 5.1.1), high-temperature distillation (5.3.2) and vacuum distillation (5.4.1). In such columns the exchange takes place between the vapour and the film of liquid falling down the walls. The possibilities and problems involved in the use of falling films have been studies in detail by Malewski [15]. 

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