I would like to add a little more to this discussion.
Last August we had a serious problem occur when a board house arbitrarily added thieving dots to one of our PCBs. This significantly reduced the spacing requirement in a safe-unsafe area. As it turned out, we did not catch the problem immediately because the hipot test did not uncover the problem. Eventually the PCB board house started using a different stamping ink on their inspection stamp that had organic content and it failed hipot. They were using stamp pad ink from the local office supply and could not immediately identify its content. As it turned out the basic board design had enough spacing (barely) because it was originally designed with 230V (L-N) systems in mind and is only used on 120V (L-N) products. We still insisted that they remove the dots from the Gerber files. In the process I learned that there are several things to watch for. 1) Thieving dots and thieving bars are used primarily for balancing copper during etch and plating and for balancing the wave during assembly. These dots may be added at the time Gerber files are generated or even edited into the Gerber files by the PCB house and never show up on a CAD system. 2) Venting of PCBs, I am not entirely clear on this but I understand that this is a modification to the ground plane and other copper fills, to allow process gases to escape from between the laminates on inner layers. Watch for changes in ground currents and reduced maximum current capability. This also has the Gerber files editing problems. 3) Inspection stamps should be epoxy based only, also adhesive labels often applied by companies to identify PCB's should not be printed with LaserJet toner! Toner is very conductive and should not be allowed to bridge safe/unsafe areas. Attached is a photo of a PCB with the thieving dots and triangular inspection stamp that failed hipot. If you look closely at the stamp you can see the trench created by the hipot test. -doug ================================= Douglas E. Powell Regulatory Compliance Engineer Advanced Energy Industries, Inc. 1625 Sharp Point Dr. Ft. Collins, Co 80525 mailto:[email protected] www.advanced-energy.com ================================= -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Thursday, January 18, 2001 7:15 AM To: [email protected] Subject: Copper Thieving Please excuse my lack of knowledge..........................what is "copper thieving"? ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
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