2 Experimental preparations

2。1 Micro roller embosser

A general purpose thermal laminator is used as a roller embosser, which consists of two rollers, i。e。  an  upper roller 1 and bottom rollers 2, as shown in  Fig。 1。  The upper roller 1 is an active roller made of steel with an embedded heater。 The bottom roller is a passive one made of hard rubber without embedded heater。 The diameter of both rollers is about 100 mm with a width being 400 mm。 The  pressure  for  embossing  and  rotation  for    substrate

Fig。 1 Equipment for micro roller embossing used in this  study。 Roller 1 was a driving roller with an embedded inner heater; roller 2 is a supporting roller made of hardened   rubber

Fig。 2 Variations of temperature on surface of roller 1 along roller width。 The measurement started from a guider and the temperature slightly increased from left to right along roller   surface

feeding can be pre-applied to roller 1 via a controller。 The pressure can be set up to 14 bars, and the feeding speed ranges from 0 to 20 mm/s。 Surface temperatures over the roller-width were measured and the stability and unifor- mity of surface temperatures were characterized by means of a portable temperature sensor。 It was found that surface temperatures actually measured were different from the temperatures pre-determined via the controller。 However, variations of the temperatures measured over the roller surface were within 2。5°C, as shown in Fig。 2, which was well acceptable。 The measured temperatures will be indicated  in the following  sections。

Fig。 3 Six identical  pattern units designed on the nickel  mold。  UL, UC and UR represent the left, central and right units in upper row; LL, LC  and LR  represent the left, central and right units in lower row

2。2 The film nickel mold

A nickel film with a thickness of 75 lm was used as the substrate for mold making。 The nickel film, the overall panel size of which was 200 mm 9 180 mm, was coated with a layer of thick photoresist, followed by UV pattern- ing, nickel electroplating and photoresist strip-off。 By precisely controlling parameters for electroplating such as solution concentration, temperature, PH value and plating current, a nickel film mold with an effective panel size of 150 mm 9 150 mm was obtained。 The height of electro- plated protrusive patterns was approximately  38 lm and the total thickness of the nickel mold was 113   lm。

There were six identical units over the effective area of the nickel mold, as shown in Fig。 3, the three units in upper row are named from left to right as UL, UC and UR, and the three units in lower row as LL, LC and LR, respectively。 Figure 4 shows an optical microscopic image of one unit UC among them。 Two groups of patterns (group A and group B) in each unit were targeted for characterization to explore pattern quality。 Group  A  includes  50 lm  line/ 200 lm pitch and 75 lm line/300 lm pitch; group B includes patterns for interconnections and passive compo- nents。 Figure 5 shows the patterns (75 lm line/300 lm pitch) in Group A, it can be seen that the patterns were about 38 lm high and uniformly distributed on the film

Fig。 4 One of the six units on the electroplated nickel mold。 Group A includes patterns of 50 lm line/200 lm pitch and 75 lm line/300 lm pitch; group B includes patterns for interconnections and passive components

Fig。 5 Pattern profiles of 75 lm line/300 lm pitch  on  the  nickel mold measured using a stylus profilometer。 The height of protrusive lines was approximately 38  lm

mold。 Figure 6 illustrates a three dimensional measurement of a square inductor in group  B。