E R Prack | PubMed Health

PubMed1993

An introduction to process visualization capabilities and considerations in the environmental scanning electron microscope (ESEM).

Process visualization can be a very powerful tool for understanding dynamic processes. Process visualization requires a non-destructive technique that can be monitored in real time. In this paper various methods of non-destructive inspection will be described and compared. The applicability of these non-destructive inspection methods to process visualization will be compared and contrasted. Particular attention will be paid to a recent development in this area, the environmental scanning electron microscope (ESEM) which is inherently a non-destructive inspection technique with the advantages of electron microscopy for superior magnification and depth of field capability. The ESEM offers a unique platform for process visualization studies. The majority of process visualization is currently done using optical microscopes with hot stages for observing morphological effects top down (optical microscopes) or from the side (contact angle). Major limitations of these optical methods include lack of magnification, poor depth of field, and clouding of optics. Process visualization is best carried out utilizing a non-destructive technique, such as the ESEM, since invasive sample preparation techniques such as conductive coatings alter the sample and make interpretation more difficult. Common process variables such as thermal profiling and the effect of ambient conditions have been examined using the ESEM. Other process variables that could be of interest in the future will be discussed. There are limitations in the ability of the ESEM to reproduce actual process conditions, such as pressure and mass flow rate trade-offs. The ESEM can also be combined directly and indirectly with other analytical techniques to determine the composition of the sample and/or byproducts of a reaction that is being monitored.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1993

Dynamics of soldering reactions: microscopic observations.

This paper provides a summary of some in situ, high-resolution studies of solder spreading reactions on microelectronic circuit metallizations. Experiments are described that focus on the use of the environmental scanning electron microscope, or ESEM. Those experiments have been complemented by studies using optical hot-stage microscopy and have been supplemented by additional analytical tools such as energy dispersive X-ray microanalysis, Auger and ESCA to evaluate chemical processes. Two general results from dynamic scanning electron microscope observations are that 1) molten solder alloys undergo a segregation process during spreading in which a "precursor" film spreads in advance of the bulk solder and 2) the spreading front, which may be enriched in Sn from Pb-Sn or Bi-Sn solders, or In from Pb-In solders, spreads along high-reactivity features of the metallization surface as a reacting "precursor" film. A third observation from these tests is that, in unconfined geometries, the reactive metallization, if not sufficiently thick, can be dissolved by the solder before wetting is complete, leading to dewetting of the solder. Both the kinetics and extent of spreading of these films and the relationship of these phenomena to the commonly measured contact angle and wetting forces are currently being examined by a range of complementary techniques. Information gathered in these studies shows that process temperature as well as composition, reactivity, and relative amounts of the solder and metallization species should all be factors of interest to the those responsible for control of soldering processes.

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