Sizes and dimensions for panelization with breakaway tabs (mouse bites)?   - Page 1
Forum section: electronics / general

author: Corporate666
author_rank: Unknown
timestamp: June 05, 2017, 06:45:57 am
content: Are there any standards or rules of thumb for panelizing boards when using breakway tabs with holes drilled on the tabs?Specifically...1) What is a standard width for the slot around the board outline?2) How wide should the tab be for a 1.6mm FR-4 PCB?3) What size drills should be on the tab? Should the drill centers be directly on the PCB outline? Or perhaps the drill diameter should be tangent to the board outline?4) How closely spaced should the drills be on the tab?5) Should the drills be on both ends of the tab (PCB side and panel side)? I've seen it done both ways - with drills only on the PCB side, but also done with drills on both ends. Is there a reason to choose one vs. the other?6) How frequently (in linear inches or linear millimeters) should tabs be placed around a PCB?And on a related note - when you folks are panelizing boards, do you generally leave the copper on the unused portion of the panel? Or put a cross-hatch or dotted fill? Do you indicate anything special on your gerbers - instructions, specifications, indicating which is the PCB and which is the panel (in case it's not obvious), etc?Comments are appreciated - just wondering how other people do it. I've winged it so far by loosely copying panelizations that were done by PCB manufacturers on my behalf. But there are a bunch of PCB's being worked on here at the moment and I'd like to learn more about the topic.

author: ebclr
author_rank: Super Contributor
timestamp: June 05, 2017, 08:14:10 am
content: http://support.seeedstudio.com/knowledgebase/articles/388503-what-are-the-pcb-panelization-rules

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 05, 2017, 08:55:12 am
content: What I use :0.5mm holes, 0.75mm apart.Length depends on panel size and number of tabs - typically 4-8 holesSlot width 2mm - this is a fairly standard size, below which manufacturers start charging more as they have to run smaller tools more slowlyIf I need a final PCB edge with no bumps ( e.g. it needs to slide into a slot in a channel) I offset the rat-bite row into the PCB and bend the ends of the slots to meet the row of holes.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 05, 2017, 09:01:34 am
content: Quote from: Corporate666 on June 05, 2017, 06:45:57 amThat depends.If you are panelising individual PCBs within the panel, so when broken out there is a PCB-shaped hole with the tabs left in the panel you should only rat-bite the PCB edge so it leaves the tabs on the waste.If you are panelising a set of PCBs such that the slot forms the edges of two adjacent PCBs, you need to rat-bite both edges of the tab. The advantage is better panel utilization, but the disadvantage is that you then have to snap off all the tab remnants after you've broken the PCBs out.

author: Corporate666
author_rank: Unknown
timestamp: June 05, 2017, 06:14:54 pm
content: Quote from: mikeselectricstuff on June 05, 2017, 08:55:12 amThanks Mike - great info. I'm spreading a few new designs among a couple different Chinese PCB houses and often times the sales people have a "yes, yes, we can do it - just send gerbers and place the order!" mentality instead of answering questions about router bit diameter for cutting slots, and drill sizes that aren't specialty and cost more - so the above info helps greatly.On the other post re: holes on one or both sides of the tab - the way you described it makes sense and was my understanding, however I've had a few board houses panelize boards where the remaining panel is discarded, and they put holes on both ends of the tab. I thought there may be a reason for that (less stress on PCB while depaneling or something), but it was probably just a habit thing on the part of the person who panelized the board for me.

author: Corporate666
author_rank: Unknown
timestamp: June 05, 2017, 06:15:56 pm
content: Quote from: ebclr on June 05, 2017, 08:14:10 amExcellent resource, thank you!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 05, 2017, 08:10:40 pm
content: Quote from: Corporate666 on June 05, 2017, 06:14:54 pmCould be because they use a standard library part, but it's also possible that to de-panel, they punch the tabs out, which would require double bites.

author: Matt-Brown
author_rank: Regular Contributor
timestamp: June 06, 2017, 04:43:51 pm
content: I work for a contract pca assembly house. We usually get single up gerbers and panelization is left up to us. The most important thing is to have an array that works with most processes and machines. We like to keep to a sheet of paper 8.5x11. for rails we use 0.3 inches or 7.62mm all the way around with 4 tooling holes at the corners and fids 3mm in all directions away from the holes (I would prefer it if most board designers added 3 fids to their boards also though and sometimes we have board houses add them also). For routed boards we almost always see the ratbites at both sides (on the rial side and on the board side). Routing a board and adding ratbites is more expensive than simple v-score. so if your board is rectangular and you dont have overhanging parts go with that option.A typical board house FR4 base is 18 inches by (I am guessing on this next measurment) 10 inches. So to not pay for weaste laminate we try and panelize and have the board house break off our arrays so not to waste so much and keep cost down.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 06, 2017, 05:31:43 pm
content: On designs where I haven't specified what kind of panelization to use, and where the outline is more or less rectangular, I almost always see v-score.Some things to be aware of:- The score has some width to it.- V-score separation can damage parts near the edge.- The scored edge is rough (the core gets torn), but it is very straight.- No copper can connect across the score (even inner layers are iffy). Keep this in mind for DFT (Mike and Dave have videos about this -- you can get traces over plain tabs and mouse bites, not others).Non-rectangular outlines are routed, and usually supported with mouse bites or small tabs.Board houses won't usually combine tab and score, but they can be very handy to specify. I like to use these when a smooth board edge is desired, and where low breakaway force is desirable, or where a separator tool can't get access (e.g., under connectors that overhang the board edge).Personally, I'd use tab-and-score all the time, where applicable, because it's just so nice and clean. It likely adds a small cost because of the extra routing, plus scoring (versus just scoring, or minimal routing to capture whatever bumps, corners or other features the outline has), so it's not necessary everywhere.As for implementation, I either add a note (arrow + text) specifying what kind of tabs to use on the required edges, or draw the tabs, with a note that they don't have to be done exactly as I've drawn, but that they should be done in this style to the usual standard. So, the position and number of tabs might be different, but I expect the same kind of tabs.Tim

author: Mattylad
author_rank: Regular Contributor
timestamp: June 07, 2017, 06:02:29 pm
content: I have used routed and scored panels lots of times, never been a problem specifying it.When you use mouse bites, you can place the hole within the board outline so that when broken the sharp little edges left are within the edge of the board so do not cath fingers when being assembled. They will also require that you consider them when placing components and routing as a clearance from them is required.Clearance is also required on scored edges, the descoring machine (pizza cutter) can require a 3mm ish gap between the edge and components - check yours.

author: wraper
author_rank: Unknown
timestamp: June 07, 2017, 06:09:43 pm
content: Quote from: T3sl4co1l on June 06, 2017, 05:31:43 pmActually you can, Mike had shown how to do it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 07, 2017, 06:40:58 pm
content: Ah, good point!Tim

author: ar__systems
author_rank: Frequent Contributor
timestamp: June 07, 2017, 09:10:10 pm
content: Quote from: wraper on June 07, 2017, 06:09:43 pmHehe, that video actually show conductors over mousebites, not over v-score.On my recent project I ran conductors across break line on bottom side and requested 2/3 depth scoring of top side only.

author: wraper
author_rank: Unknown
timestamp: June 07, 2017, 09:33:32 pm
content: Quote from: ar__systems on June 07, 2017, 09:10:10 pmHehe, you didn't watch the video or even look on the thumbnail.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 07, 2017, 10:58:53 pm
content: Quote from: wraper on June 07, 2017, 06:09:43 pmThat didn't actually work out very well in the end - some of the plating did get mangled - I wouldn't recommend it without further experimentation and some redundancy.We changed to a routed panel for production - tracks over ratbites were fine but I didn't want to risk teh v-score for the 14K strips we made.