Jerry, A many years ago I was involved in determining if traces, tracks, or etch could be used as a fuse. The testing we did was very controlled. The testing results proved it was impossible to predict with any confidence. The etch would not open without destroying the PWB, causing a fire or other more catastrophic destruction. We used PWB from 9 vendors the results had so much variation it was impossible to predict when and under what conditions the etch was going open reliabley. Controlling the spread of molten metal and the de-bonding of etch that shorts to other circuits is impossible.
Covering the area with fish paper does not solve the problem. The problem is the etch itself. Regardless of the energy present anetch fuse is un-reliable. In fact the higher energy is usually more of a problem than lower energy. Unless the laws of physics have been re-written an etch is unpredictable and un-reliable. An etch is NOT acceptable as a fuse by UL or IEC 950. Duane Marcroft Telecom and Data Communications Consultant Peer Communications [email protected] > > >On June 5 Jerry Martin wrote: > >We are designing a product that will be used in a Network Interface >Device (NID) that mounts on the outside wall of a house. The enclosure >will be a 5V material and the customer will not have access to the >network circuitry. > >We would like to submit the product to UL 1459 (knowing that it will be >replaced by UL 1950 in April, 2000). > >With so much energy available during the overvoltage test, we're >concerned that etch will open. Is it o.k. if the etch opens and we pass >the dielectric strength test afterwards? The enclosure will be covered >with cheesecloth and there is no way for flaming particles to get out. > >Thank you for your replies, > >Jerry > >Jerry, > >Having etch open is not considered a passing condition. There have been >discussions where people try to use etch as a fuse. Safety agencies do not >accept that construction since there can be manufacturing inconsistancies. >Sometimes the etch can peel off the board and short something else, >causing even >a worse hazard. > >I would be concerned about an etch that would blow before the wiring >simulator >fuse, usually a Bussman MDQ 1.6 A Time Delay fuse. > >Opinions expressed are my own, and not those of my employer. > >Eric Petitpierre >Pulsecom >Herndon, VA >[email protected]
