The document describes research into fabricating micro vias in LCP substrate using mechanical punching and subsequent cleaning. Chemical etching using sodium permanganate and sodium hydroxide was found to effectively remove LCP and copper burr leftovers from punching. However, carbonated LCP debris remained. 30 minutes of oxygen plasma cleaning at 125 watts power successfully removed the debris, yielding uniform via walls. The sequential process of wet etching and plasma cleaning was necessary for clean micro via fabrication using mechanical punching.

1. The 60 th ECTC Paris Las Vegas, Nevada, June 1 - 4, 2010 Investigation of Chemical De-burring and Subsequent Plasma Cleaning of Mechanically Punched Micro Via Array Fabricated in LCP Substrate Mohammad K. Chowdhury , 1 Li Sun, 2 Shawn Cunningham, 2 and Ajay P. Malshe 1* 1 Materials and Manufacturing Research Laboratories (MMRL) University of Arkansas, Fayetteville, AR 72701 2 WiSpry Inc., Irvine, CA 92618 * Contact: E-mail: apm2@uark.edu, Tel: (479) 575-6561, Fax: (479) 575-2669 Chowdhury , Li Sun, Shawn, and Ajay

4. How The Punching System Works? Chowdhury , Li Sun, Shawn, and Ajay µ -Via Fabrication by Mechanical Punching: Die Bushing Pin LCP Copper Copper LCP Copper Copper Before Punching Copper Copper LCP After Punching APS 8718 Automatic Punching System Pacific Trinetics Corporation 6” x 6” Sample Holder Punch Pin Holder & Die Bushing LCP Copper Copper LCP Copper Copper Copper Copper LCP Figure: Uniform and nice via formation

5. Driver Applications: Chowdhury , Li Sun, Shawn, and Ajay Ref:http://www.mpdigest.com/issue/Articles/2009/june/mmic/Default.asp In MMIC (Microwave Monolithic IC) Ref: http://www.pcdandf.com/cms/magazine/220-2009-issues In 3D Packaging & MCM Module Ref:http://www.cmst.be/projects/img9.jpg In Flexible Electronics Ref: http://www.techwear-weblog.com In Wearable Electronics www.smalltimes.com In RF-MEMS Devices in Cell Phone www.ec.europa.eu – ANASTASIA Project In Satellite and Aerospace Applications

10. Chemical Etching Using Promoters Chowdhury , Li Sun, Shawn, and Ajay 75 µm Via, 187.5 µm Pitch, 10 x 10 Array PROMOTER 3308A (20 – 40 % NaMnO 4 ) @ 85 0 C PROMOTER 3308B (NaOH < 30%) @ 85 0 C 3314 Neutralizer (3% H 2 SO 4 + 3% H 2 O 2 ) 5 Min 1 Min 5 Min 5 Min 10 Min 15 Min PROMOTER 3308A (20 – 40 % NaMnO 4 ) @ 85 0 C PROMOTER 3308B (NaOH < 30%) @ 85 0 C 3314 Neutralizer (3% H 2 SO 4 + 3% H 2 O 2 ) 1 Min 5 Min 5 Min 5 Min 10 Min 15 Min PROMOTER 3308A (20 – 40 % NaMnO 4 ) @ 85 0 C PROMOTER 3308B (NaOH < 30%) @ 85 0 C 3314 Neutralizer (3% H 2 SO 4 + 3% H 2 O 2 ) 5 Min 5 Min 1 Min 5 Min 10 Min 15 Min

23. Summary of µ- Via fabrication Micro via fabrication by mechanical punching 5 Minutes Oxidation of the LCP burr by 20 – 40% NaMnO4 Chowdhury , Li Sun, Shawn, and Ajay 5 Minutes Etching of the LCP burr by < 30% NaOH 5 Minutes Neuratilzation by (3% H 2 SO 4 + 3% H 2 O 2 ) 30 Minutes oxygen plasma cleaning with 125 watt power at 320 mili torr pressure with 160 sccm of oxygen flow