Circuits Assembly - July 2008 - (Page 38)

PWB Rework ‘Web Circuits’ Mike Buetow Avoiding re-spins is made easy and economical through a novel additive process. A large network systems company had a single prototype PCB to prove out its design change before re-spin and ordering new prototypes. However, the change required traces connected to BGA pads under the device to be brought out and new SMT pads installed. · One of North America’s largest electronics firms has production scheduled with its Mexican EMS provider and 6,700 RoHS PCBs are in the supply chain. Traces and SMT pads need to be added and reliability is a major concern. · Another major company has five boards with OSP finish requiring four additional components and the boards. While most companies in these situations would opt to re-spin the design, cost and time often make that a gut-wrenching decision. Laconia, NH-based Additive Circuits (additive.com) believes it has a less expensive, more elegant solution. “Web circuits” are the brainchild of Art DesMarais, founder of Additive. His concept calls for installing solid copper traces and SMT pads between existing pads, vias and through-holes – basically, anywhere an interconnection is needed on the unpopulated board. The process, he says, costs a fraction of a re-spin and reworked boards can be turned around in days. Avoiding the re-spin starts with the Gerber files and engineering change orders. Although Additive works only with bare boards, the company provides customers with a range of known design rules, everything from conductor width and spacing to the eventual component placement soldering operations. “We’re concerned with the assembly, the compatibility with it,” says DesMarais. Once the CAD files are in place, unwanted traces are deleted and designated pads are isolated, including inner-layers. Then comes the web circuit process. The “web” starts with 1 oz. electrodeposited copper foil that conforms to IPC-4562. The foil is mechanically etched into the shape, length and width of the to-be-installed traces. This is also where the web circuit gets its name. “The circuit is held together with tabs,” explains DesMarais. “If the tabs were broken, it would fall apart, like a spider web.” The process can add circuits on outerlayers, but also can perform etch cuts on innerlayers and pad isolations. Mechanical end-mills with computer x,y and z control are used for cuts, which DesMarais finds faster and more cost-effective than lasers. Next, an isolation layer made from B-stage epoxy Figure 1. Used to avoid design re-spins, Web circuits can connect BGA pads … circuitsassembly.com 38 Circuits Assembly JULY 2008 http://additive.com http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - July 2008

Circuits Assembly - July 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business Global Sourcing On the Forefront Screen Printing Tech Tips Will Electronics Follow the Sun? ‘Warm’ Manufacturing Heats Up Reputation Trumps Recession, China ‘Web Circuits’ A Novel Non-VOC Conformal Coating Krypton: Benchmarking Customer Satisfaction 2008-09 CIRCUITS ASSEMBLY Buyers Guide Wave Soldering Pb-Free Lessons Learned Process Doctor Materials World SMTA Int'l Product Preview Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - July 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.