Mail*Link(r) SMTP FWD>DES/FAB/ASSY: Ruggedized Revisited Jeff, Sorry, but in my previous response I forgot to include some thoughts/experiences on component mounting on the PB itself. In the past, we've "ruggedized" many commercial/industrial Class 2 products to withstand the rigors of some of our R&D environments. Generally shock/vibration is the major concern and therefore, the "ruggedization" of the component mountings need to be considered for PBA's being subjected to shock and vibration is a major concern. Vertically Mounted Axial Leaded components: Some of the concerns are vertically mounted, axial leaded components. The greater the mass the greater the problem. Lay them flat against the PB if possible, if not stake at least a couple (three preferred and hopefully in a "triangular" layout) together using a non-corrosive RTV staking adhesive. lllll aaaaaaa aaaa l l cccccc cccccc ccccc l where the "a"s are the staking adhesive c c c c c c l c c c c c c l the "c"s are the component body c c c c c c l c c c c c c l the "l"s are the component leads cccccc cccccc ccccc l l l l l l l the "pb"s are the printed board pbpbpbpbpbpbpbpbpbpbpbpbpbpbpbpb l l l l l l It is best if the components can be bonded together to for a tetrahedronal-like truss for "mutual" support. Also, becareful with power semi's, especially the TO-220 like families, in particular those that have clip/slide-on cooling sinks, use a cooling sink that mounts into the PB. In some cases, you have large "single" components that are mounted away from everything else (isolated) and there is no way to obtain "mutual" support, in these cases, sometimes it is possible to add a fastener mounted "standoff" (or brace) along side the component and use either a staking adhesive to bond the component to the standoff or to use a plastic cable tie-wrap(s). A couple of times we needed to "ruggedize" normal Class 2 for limited-use automotive like environments and there wasn't room to add "standoff's". So we adhesive bonded 3 diagonal braces from the top of the component to available open areas on the PB, it didn't look great, but for R&D applications, it worked. Horizontally Mounted Components Observe the mass/component lead requirements in IPC's design and assembly spec's. Most components up to a 2W resistor like size are not a problem. Large electrolytic capacitors, radial or axial leaded can be a concer. Tie them down or adhesive bond them. Large power resistors and inductors are sometimes mounted 6mm and more off the surface of the PB --- it's a disaster. For power resistors, it's done so as not to burn holes in the PB base material. For inductors it to provide cooling and to reduce the distributed capacitance across the inductor. Though most of you aren't into high voltages (>a few hundred volts) it controls the electrical spacing. For high impedance analog stuff, it reduces the capacitance controls the insulation resistance for high valued feedback resistors (Rf) [Rf -- that's not radio frequency that's electronickers shorthand for the feedback resistor] in analog amplifiers. These pose real problems, but you need to either mount them lower or provide some kind of support for them. For example: ccccccccccccccccccccccccc --c c-- where the "c"s are the component body l ccccccccccccccccccccccccc l l ssss ssss l the "-"s & "l"s are the component leads l ssss ssss l l ssss ssss l the "s"s are low dielectric constant plastic l ssss ssss l spacers that are adhesive bonded to the PB pbpbpbpbpbpbpbpbpbpbpbpbpbpbpbpbpbpbpb and to the component body. l l the "pb"s are the printed board Avoid the use of "plug-in" socketed components and connectors, or use one's with shock/vibration restraints or use a staking adhesive to hold the mated components in place using a non-corrosive staking adhesive (we genrally use RTV's). Hope this helps, Ralph Hersey e-mail [log in to unmask] -------------------------------------- Date: 7/22/96 4:41 PM From: Jeff Seeger Hello, TechNet! I have a situation where our customer is being asked for "ruggedized" product. The product category is generally Type 3 and 4 PWB's, with Class 2 expectations, fine pitch components both sides, (of course) moderate high-speed rules. Product is built in ~100 piece lots. Is there a general scheme of "ruggedizing" the PWA, or does this simply imply an upgrade to Class 3 standards? I'm not sure density will allow a full Class 3 implementation. Is there anything non-subjective about "ruggedizing"? I've not seen it mentioned anywhere. Would selective upgrades to Class 3 qualify as "ruggedized"? Which areas? Of course, I have no specific performance requirements, just the word "ruggedized". From the nature of the product, I would guess there could be application for mobile equipment. Can any "rugged" folks out help an old soft-in-the-head design guy? Thanks alot, and best regards, Jeff Seeger Applied CAD Knowledge Inc Chief Technical Officer Tyngsboro, MA 01879 [log in to unmask] 508 649 9800 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** ------------------ RFC822 Header Follows ------------------ Received: by quickmail.llnl.gov with SMTP;22 Jul 1996 16:40:22 -0700 Received: from ipc.org by simon.ipc.org via SMTP (940816.SGI.8.6.9/940406.SGI) id SAA00449; Mon, 22 Jul 1996 18:30:23 -0700 Resent-Date: Mon, 22 Jul 1996 18:30:23 -0700 Received: by ipc.org (Smail3.1.28.1 #2) id m0uiTXY-0000MUC; Mon, 22 Jul 96 17:33 CDT Resent-Sender: [log in to unmask] Old-Return-Path: <simon.ipc.org!bort.mv.net!rapidcad!jseeger> Date: Mon, 22 Jul 96 18:24:35 EDT Message-Id: <[log in to unmask]> From: "Jeff Seeger" <simon.ipc.org!bort.mv.net!rapidcad!jseeger> Subject: DES/FAB/ASSY: Ruggedized PWA's To: [log in to unmask] X-VMS-Mail-To: UUCP%"[log in to unmask]" Resent-Message-ID: <"MVZMh2.0.TM6.f60zn"@ipc> Resent-From: [log in to unmask] X-Mailing-List: <[log in to unmask]> archive/latest/5303 X-Loop: [log in to unmask] Precedence: list Resent-Sender: [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************