If you have ever examined any of our previous materials and processes courses you will realise that this grouping of what we have called Enabling processes is something that is new to this module. Why have we done this?
The thought processes started as a result of a trip to our old friends DEK Printing Machines at Weymouth, when the comment was made that most of the printers sold are not used for solder paste. Now in all previous courses, stencil printing had been described as the first stage in the assembly process, and screen printing (if at all) as used for applying legend to print circuit boards. This ignored the use of the same process in making chip components and thick film circuits, and for applications such as coding.
Not only is screen/stencil printing used in a number of applications, but it is actually only one of the number of different patterning processes. Some of these are alternatives, whilst on other occasions multiple processes are used. For example, solder mask may be applied overall by double-sided screen printing, and patterned by photoimaging.
This led to the decision to pull together all the patterning approaches, and discuss the general issues, such as the nature of the surface, the area of the deposit, and the thickness and evenness of deposit required. This allows alternative printing processes, and alternatives such as dispensing to be considered at a basic level, independent of any particular application. The benefit is that it becomes easier to explain the issues involved in modified and new processes, and to see the commonalities between the different applications.
So patterning became our first “enabling process”, to which we have added a number of others, plating, component placement, joining techniques, cleaning techniques, and methods of providing protection. We have also taken a brief look at the processes used to make mechanical elements of the assemblies.
In this Unit you will find a description of the processes and their applicability, and the major factors involved in their use. In order to avoid duplication, each of the succeeding units focuses on aspects of the materials and processes that are fundamental to the topic under consideration. We have not repeated any of the material in this section, though we have provided links.
For example, in the section in Unit 6 that refers to solder paste printing, we have talked about the solder paste itself, about handling and storing paste, and cleaning the stencil, whilst the generic material on printing in this unit looks at different stencil types, at paste release, and at machine setting to get the right results, because these aspects apply to all materials and not just to the paste used for this particular process.
A consequence of grouping information in this way is that the background material to this unit is extensive. Bluntly, if you follow every link pedantically you will get left behind! So we encourage you to read the top-level material, and explore further only when it is needed at a later stage, or if you are aware of major gaps in your prior knowledge. As with the Materials of electronics unit, be selective in your preliminary reading, but make yourself aware of where supplementary materials are to be found.
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