Ian, In my former life, we used metal enclosures, metallized plastic enclosures; and we even used a metallized fabric liner affectionately called the "EMC diaper" in one case.
All three of these solutions will usually provide the required sheilding effectiveness over large expanses of surface. What you need to do is: 1. Determine how you will mate separate parts of the case to continue the shield. 2. Determine if the coating is galvanically compatible with any metal parts that come in contact. 3. Plan for recycling if you are shipping to Europe. Some coatings recycle better than others. 4. Plan for your desired environmental specs. Some coatings will flake and/or peel under certain conditions like salt spray. Some plastics may not hold up very well if your product is to be used in extremely high (deformation) or low (brittleness) temperatures. 5. Plan for safety. If you need to pass safety testing, ensure that you use a coating application vendor that has a current UL card for applying the coating that you want to use to the plastic that you want to use. 6. Watchout for overspray. Keep the painted surfaces painted, keep the conductive surfaces clean. 7. Watchout for short circuits. One of my co-workers wanted to experiment with coated plastics, so he just grabbed some cases out of stock and sent them out to be sprayed. When he used them, he almost had a fire because the vendor dutifully coated the inside of the battery box...which short circuited all of the batteries when installed. 8. Intangibles...If you use a coating, you may have to figure out some creative ways to ground shield tails for keypads, ground circuitboards to the chassis, ground connectors to the chassis, etc... In general, with the type of equipment that I used to work with; metal casework was just as much of a hassle as coated plastic; this was because many of the problems outlined above are indiginous to both metallized plastic and metal chassis. In my experience, I used a few different coating methods with the following results: Electroless plating ...excellent conductivity and adhesion...high initial cost...meant for high quantities Aluminum Vacuum Depositing ...good conductivity and adhesion...medium cost...good for medium quantities Spray on coatings ....good conductivity ... adhesion was fair...low cost...generally easiest for prototypes and small quantities Best regards, Chris Maxwell > All > We are hoping to move from metal to coated ABS enclosures for various > products as these provide a significant cost saving. Thus I would welcome > any comments as to how to ensure that the coated ABS versions are as > resilient from an EMC point of view as the metal ones. > In general is it possible to achieve the same shielding effectiveness from > a > coated ABS enclosure as from a metal one? > > Ian Gordon > > > > *********************************************************************** > The information contained in this email and any attachments may be > confidential and is provided solely for the use of the intended > recipient(s). If you are not the intended recipient, you are hereby > notified that any disclosure, distribution, or use of this e-mail, its > attachments or any information contained therein is unauthorised and > prohibited. If you have received this in error, please contact the sender > immediately and delete this e-mail and any attachments. > > No responsibility is accepted for any virus or defect that might arise > from opening this e-mail or attachments, whether or not it has been > checked by anti-virus software. > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Jim Bacher: [email protected] > David Heald: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
