Product Property Measurement Techniques

One of the major challenges associated with micromoulded products is how to quantify the geometric, mechanical and morphological properties of the products. The physical size of these products negates the use of conventional testing methods and alternatives must be sought.

The first stage of product assessment is usually performed during commercial micromoulding processes with a machine vision system, which typically consists of a CCD camera system linked to a PC. Each product is presented to the camera following ejection from the mould where it is matched against a number of dimensional criteria such as area pixel counts, correlation with standard polygonal primitives or critical chord lengths. These techniques offer an initial quality assessment integrated into the manufacturing process based on the net shape of the product , but cannot provide information regarding the structural integrity of the part, which may be influenced by variations in material morphology or the presence of impurities.

A more accurate measurement of the geometry of a product can be determined using a full 3-dimensional assessment technique such as atomic force microscopy or white light interferometry. These surface measurement systems provide 3D coordinates for a surface with nanometer resolution, but are time consuming and difficulties faced with integrating them into a production environment currently limit there use to a strictly off-line capability.

Generating mechanical property data from a micromoulding product cannot be performed using standard testing techniques due to the physical size of the products. Currently, this problem is addressed using nanoindenting which is a technique that sees common use in the characterisation of thin films. Such techniques do not, however, provide a bulk measurement of the mechanical properties of the product - they only penetrate a small way into the sample which correlates with the skin layer on a micromoulding, which may behave differently to material in the centre of the part due to differences in the thermal history. This can only really be addressed using a sectioning technique which exposes internal surfaces and allows hardness and modulus assessment through the thickness of the product.

White Light Interferometer image of an AFM tip