CircuiTree - January 2009 - (Page 19) Tech Talk other spaces separating circuits. The use of pulsed sprays (Impulse Process, LP-Chemie) was mentioned in Part A. Because the pulsed sprays increase the etch rate in narrow spaces, this technique will reduce etch rate differences due to circuit patterns. Another interesting approach is the combination of chemical etching and electrochemical etching (or de-plating) as described in Reference 5 (see Figure 7). The board, covered with a resist pattern, becomes the anode in a plating cell that also contains an etchant. Chemical etching is slow in narrow openings in the resist, and it is faster in wide open areas. With electrochemical etching, on the other hand, the etch speeds are reversed: small openings in the resist (i.e., small copper features surrounded by large resist areas) are areas of high current density as indicated in Figure 7 by the higher density of field lines. Here, copper de-plates (corrodes) faster than in wide open areas of lower current density. So the differences in chemical and electrochemical etch rates offset each other, resulting in more uniform etching. ■ Figure 7 Combination of Chemical and Electrochemical Etching which is undesirable. One approach to avoid this, assuming the design allows enough room for it, is to flank the outside, functional lines with nonfunctional (dummy) lines (see Figure 6). Now the nonfunctional lines will over-etch, which is of no concern. The same concept can be applied to the Siemens and Atotech panel plate/tent and etch processes mentioned in Part A. These processes make use of laser ablation of an immersion tin or organic etch resist. Instead of laser ablating all non-wanted copper, which consumes a lot of time, one can separate a circuit line from nonfunctional, large copper areas by ablating only a small gap, forming a space of equal width to the References Please visit www.circuitree.com to view the references for this column. Karl H. Dietz is CircuiTree’s technical editor. Email karl.h.dietz@USA.dupont.com bnp Trade EDUCATION Showcase your expertise, introduce new products or programs, or suggest new business opportunities. BNP Media provides the editorial, design, and distribution via our leading magazines. CUSTOM MEDIA Custom Media Group creates The BNP custom media solutions using rich content and innovative media to build relationships and t lt Every project i t k and j t is turnkey d create results. E mapped to your marketing goals and budget. BNP Custom Media combines the power of over 60 media brands, extensive vertical market readership, expert editorial and award-winning design into one powerful media package. Custom MAGAZINES Go beyond an expensive catalog and take the lead in your business segment by publishing your own magazine. BNP Media provides the editorial, design, and distribution horsepower; you provide the direction. Commemorative PUBLICATIONS Celebrate anniversaries and milestones with custom publications that tell your story in a rich, colorful way. BNP Media has extensive experience with commemorative books and publications. Integrated MEDIA All BNP Custom Media can be formatted for the Web. In addition, choose from Web-only content and features to target your message and increase your online exposure. FOR MORE INFORMATION CONTACT: Steve Beyer, Director BNP Custom Media O: (847) 516-1977 C: (630) 699-7625 beyers@bnpmedia.com circuitree.com • January 2009 CP0708HouseAd_7-25x4-875.indd 1 Untitled-1 1 19 7/2/08 8:42:13 AM 6/20/08 3:31:18 PM http://www.circuitree.com http://www.circuitree.com
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