While micro-scale technologies were well established in the semiconductor and microelectronics fields, the same cannot be said for manufacturing micro features and products in materials different from silicon.

These technologies are generally classified as MicroEngineering Technologies (MET) and refer to the creation of high-precision three-dimensional (3D) products using a variety of materials and possessing features with sizes ranging from tens of microns to a few millimetres (See Fig. 2.3).

There is no clear agreement either defining the micro engineering or what a micro product or micro component is considered. Most authors talk about micro engineering simply in terms of size but L. Alting et al. [9] gave a more general view that has been accepted in this thesis.

Micro engineering is closely related to the whole process of conception, design and manufacture of micro products and thus, cannot be totally expressed without a definition of the concept of micro product itself.

It is difficult to give an exact definition of a term that seems to be only size-related in a rapidly changing era. The definition should, therefore, contain the philosophy and characteristics of a micro product. Of course a micro product is characterised by small dimensions, either of the product itself, or of functional features or structures of the product.

From a geometrical point of view, micro products can be classified as two-dimensional structures (2D) (optical gratings), 2D-structures with a third dimension (2½D) (fluid sensors) and real three-dimensional structures (3D) (components for hearing aids). The geometry affects the possible manufacturing methods and the associated production support in terms of handling, assembly and metrology.

Another important characteristic of micro products is integration. The reason for miniaturization has to be taken into account in order to distinguish between those products that need to be “small” to reach a more compact and portable version, and those products whose functionality is achievable only by virtue of their small dimensions.

Finally, a micro product is usually constituted by several components. Thus it is apparent to distinguish between a micro product and a micro component.

Thus, the definition of micro engineering accepted is as follows: Micro engineering deals with development and manufacture of products, whose functional features, or at least one dimension, are in the order of μm. The products are usually characterised by a high-degree of integration of functionalities and components.

The creation of truly three-dimensional miniature parts with a high aspect ratio is always a challenge in micromachining in terms of achievable accuracy and relative accuracies. Whereas the absolute accuracy (feature size) that can be reached in micromachining is excellent from millimetres range down to less than 1 mm, the relative accuracy is rather bad. In traditional manufacturing of precision parts; relative accuracies of 10-6 can be attained, but these relative accuracies cannot be reached in micromachining [10]. Fig. 2.4 shows habitual range of sizes to clarify about the range of sizes, accuracies, and relative accuracies one talks in micromachining.

With some processes, surface finishes as good as 1 nm can be created, which are approximately ten times the size of an atom. If the relative accuracy of a house, which is not considered to be a precision part is compared with the relative accuracy of a lithography based micromachine, it is noticed that both are approximately the same. The optimum level in relative accuracies is usually achieved at sizes that are bigger than micromachined features. In general, it is seen that the smaller the micromachined part is, the more difficult it is to achieve a good relative accuracy.

Previous /  Next