Abstract This paper presents a micro roller embossing process for patterning large-area substrates of laminated green ceramic tapes。 The aim of this research is to develop a large-area microstructure formation technique for green ceramic substrates using a thermal roller laminator, which is compatible with screen printing apparatus。 A thin film nickel mold was developed via photolithographic pattern- ing and nickel electroplating on a 75-lm-thick nickel film。 The mold had an effective panel  size  of  150 mm 9 150 mm with the height of plated protrusive patterns being about 38 lm。 Formation of micro patterns was successfully demonstrated over the whole panel area on laminated green ceramic tapes using roller embossing。 Micro patterns for inductors, heaters as well as interconnection with 50 lm line-width were embossed on green ceramic substrates。 By means of tuning process parameters including roller tem- perature, applied pressure and feeding speed, we have demonstrated that micro roller embossing is a promising method for patterning large-area green ceramic  substrates。76179

1 Introduction

Low temperature co-fired ceramic (LTCC) materials have been widely used for multi-functional substrates, and are becoming more and more attractive for a variety of emerging applications such as microfluidic devices and three    dimensional    modules    for    power      electronics

(Gongora-Rubio et al。 2001; Smetana and Unger 2008)。 To meet various application-oriented needs, it is becoming increasingly important to develop alternative different processes for patterning unfired green ceramic tapes (Imanaka 2004)。 The conventional methods for fabricating micro vias and cavities on inpidual green ceramic tapes are mechanical punching (Wang et al。 2006) or laser dril- ling (Hagen and Rebenklau 2006)。 However, these methods have limitations, for instance, the minimum depth of gen- erated patterns is restricted by the thickness of a green ceramic tape; and the lateral dimensional of a minimum feature is limited by the sizes of punching needles or laser beams。 Formation of non-circular micro patterns such like micro channels or wedge-shaped patterns is more chal- lenging for both mechanical punching and laser   drilling。

One of alternative methods to generate micro patterns on green ceramic tapes is using micro embossing process (Cameron et al。 2006), which has been used increasingly to fabricate microstructures on polymers (Charest et al。 2004; Worgull et al。 2005; Datta and Goettert 2007)。 Micro embossing for patterning green ceramic tapes will enhance the advantages of LTCC as a substrate material。 Several research groups have demonstrated the feasibility of pat- terning green ceramic tapes using simultaneous embossing,

i。e。 to emboss an overall panel simultaneously with a rigid mold; micro pillars and wedges have been patterned on green substrates (Andrijasevic et al。 2007; Rabe et al。 2007)。 However, being composed of ceramic-based pow- ders and polymeric additives, green ceramic tapes are flexible with low strength。 This flexibility and low strength will increase the difficult in demolding; an embossed green substrate could be possibly torn up or seriously warped during demolding。

In this study, we proposed to generate micro patterns on large-area  green  ceramic  substrates  by  means  of   roller

embossing Roller embossing is an emerging technique for manufacturing polymer-based microsystems (Tan et al。 1998; Chang et al。 2006)。 Comparing with the simulta- neous embossing mentioned above, the advantages of roller embossing, especially for patterning green ceramic sub- strates, are: (1) localized embossing area that eases difficulty in demolding; (2) localized contact with heater so that only a small area of substrate is heated; (3)  reduction in limitation of substrate size; (4) lower embossing force。 A thin nickel mold was developed via nickel electroplating protrusive patterns on a nickel film of 75 lm thick。 The mold has an effective panel size of 150 mm 9 150 mm, which is compatible with the panel size of standard screen printing。 Formation of micro patterns was successfully demonstrated using roller embossing on laminated green ceramic tapes (HL2000 from Heraeus) over the whole panel area。 Micro patterns such as inductors and heaters were formed on the green ceramic substrates。 The achievements demonstrated that micro roller embossing  is a promising method for patterning large-area green ceramic substrates。