Manufacturing Processes Multiple Choice Questions on “Abrasive Jet Micromachining – 5”.
1. Elastomer masks are provided in the form of foils.
a) True
b) False
Answer: a
Clarification: These types of mask usually provided in the form of ready-made foil with self-adhesive properties. Besides, elastomers can show ductile, elastic and brittle behaviour and experiments have to be carried out under relevant practical conditions.
2. Photo-resists are _____ materials.
a) photogenic
b) photosensitive
c) photo-dissociate
d) photo-emissive
Answer: b
Clarification: Photo-resists are photo-sensitive materials. There are two types of photo-resists; positive and negative. The major drawback is that it needs Expensive equipment to prepare the mask.
3. Positive resists are formed when resist is exposed to UV light.
a) True
b) False
Answer: a
Clarification: For positive resists, the resist is exposed with UV light wherever the underlying material is to be removed. In these resists, exposure to the UV light changes the chemical structure of the resist so that it becomes more soluble in the developer.
4. After treatment with UV light, resist is washed away by the developer solution.
a) True
b) False
Answer: a
Clarification: The exposed resist, after UV treatment is washed away by the developer solution, leaving windows of the bare underlying material. In other words, “whatever shows, goes.” The mask, therefore, contains an exact copy of the pattern which is to remain on the wafer.
5. SU-8 is most commonly used negative resist.
a) True
b) False
Answer: a
Clarification: Negative resists behave in just the opposite manner as that of the positive resists. Epoxy-based SU-8 is one of the good negative resists. It is able to provide features with high aspect ratios (>10) with UV-lithography.
6. Structures with high aspect ratios are possible with _____
a) photo-resist material
b) metals
c) elastomers
d) porous silicon
Answer: b
Clarification: Stainless steel masks are very suitable for high particle velocities and fast machining operations. Structures with high aspect ratios are achievable due to the low erosion rate of steel. Attention has been paid to the adhesive layer, which should not only stick the two materials together but also avoid under etching.
7. Feature is the major drawback of metal masks.
a) True
b) False
Answer: a
Clarification: The limiting factors for all metal masks are the feature and the structuring procedure where no free-standing contours are possible. Metal masks should be applied preferably for medium and large sizes.
8. Elastomers are suitable for high air pressures.
a) True
b) False
Answer: a
Clarification: Elastomer foils are easy to pattern and allow a high complexity of the design but the procedure is somewhat time consuming. They are not suitable for high air pressures due to their elastic deformation behaviour.
9. At higher particle velocities, adhesion between the mask and the workpiece material becomes weak.
a) True
b) False
Answer: a
Clarification: The adhesion is significantly weaker for complex patterns and higher particle velocities that may cause a release of the foils from the substrate. Their applicability is limited to single workpieces and feature sizes down to 75μm.
10. High aspect ratios are not possible with SU-8 material.
a) True
b) False
Answer: a
Clarification: A good compromise in terms of feature size and imaging accuracy gives the epoxy based photo-resist SU-8. Since the maximum thickness of an SU-8 layer is about 300μm, no high aspect ratio is achievable and its application is limited to shallow cavities.