Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


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Tab-Routing | 20 February, 2006

Histroically we have designed our pcb panel configurations around the v-score format. The QA Dept of our company is is suggesting that we revert back to tab-routing as away to avoid damage to senistive components like large package ceramic capacitors during depanel. Most of our mfg sites have routers, but our design sites do not and are looking at purcahsing nibblers as one option since they tend to deal in low-volume builds. Before we proceed going with tab-route designs, I want to establish a set of "design rules" for the engineering teams. Are there rules for specifying tab locations, tab sizes/widths, and route/slot dimensions - etc? Or is all of this a standard function of the CAD software & libraries you use? I have looked around the Internet at nibblers and other systems, but do not see any rules other than a few notes about mouse-bites?

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Tab-Routing | 22 February, 2006

Tricky question. 1. If you are using fiducials on the snap-off areas then try and have the tab adjacent to these. 2. In many instances your tab locations will be determined by the case in which you are fitting the PCB. You don't want to be filing down the tab stub where it interferes with the housing. The position of card fingers, tracks, pads, shields etc may also be a factor. 3. PCB thickness, size and layout will also be a factor. 4. In general go as thick and as often as you can, keeping in mind you have to cut them out at a later date.

If you can; get your fabricator to do a bare board, (no plating or drilling for cost reasons), mock-up of the design and run these through the oven or wave several times at different angles to see what happens. Once you are satisfied with the result and have several production runs under your belt you may wish to consider having a punch tool made to do the operation in one step - routing takes time and adds costs. You will have to figure out if you can recoup the cost of the tool. Try starting here: 1.6mm to 1.00 mm thickness PCB use a 3mm wide tab of <5mm length every 50mm. Less than 1mm thickness space them every 40mm. The stiffer you make the panel the better for the production staff.

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Tab-Routing | 22 February, 2006

Here's your design rules: * IPC-2221 * IPC-2222

Bonus is that they include the works, not just break-away tabs

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