Tight fitting Backplane dimensions (IEEE 1101 Subrack) / Panelizing - Page 1
Forum section: electronics / general

author: adrifromhh
author_rank: Contributor
timestamp: December 19, 2018, 12:14:18 pm
content: Hello, I hope this is the right subforum.I'm constructing a modular backplane for a 19'' subrack. Each slot, 4 units wide, has it's own backplane segment which houses the DIN 41612 connector.The standard IEEE 1101.1 tells me the width of a 4 unit frontpanal should be: 4 x 5.08 - 0.3 [+0 / -0.2] = 20.02 mmI'm planning to order at JLC PCB. They specify their outline milling / v-scoring precision at ±0.2mm.Please have a look at the attached picture of the board.The curved shape of the board is my solution to the 7.62 mm distance from the sidewall of the subrack to the first mounting hole. The boards are supposed to be mounted very easily. This way you can just align the first one to the side wall. (I hope)My questions are:How much clearance should I have between each segment so ensure them fitting nicely besides each other?I want to panelize the boards before manufacturing. Would you put the V-score at the top and bottom? The boards have to fit exactly in the subracks mounting rails. (128.7 mm +0/-0.3)

author: adrifromhh
author_rank: Contributor
timestamp: December 20, 2018, 11:21:50 am
content: Anyone? I thought this was a pretty straight forward question.How much clearance should i leave between pcb's that are supposed to be fitted tightly next to each other?

author: Rerouter
author_rank: Super Contributor
timestamp: December 20, 2018, 12:03:00 pm
content: Quote from: adrifromhh on December 19, 2018, 12:14:18 pmClearance is generally based upon how much flex your rail system and board give, the Idea is that when its being moved and jostled about, the boards should not flex enough to contact one another, e.g. electrolytic capacitor tops with throughole solder joints of the next board. for this I would say 0.5mm - 1mm depending on your manufacturing method, skewing closer to 1mm if you plan to double load and dont have an offset already planned into your front plates,For similar reasons you generally will see higher components set back a bit from where the rails start, this is because the board can be quite unparrellel at insertion, and you both dont want to hit the next cards components, and dont want to damage components near the backplane connector until its properly being guided.As for V-scoring, the edge is going to be rough, plan atleast 0.06mm of margin on vscored edges, if you need perfect dimensions you need routing.

author: adrifromhh
author_rank: Contributor
timestamp: December 20, 2018, 02:12:34 pm
content: Thank you for your reply!I think you got my question a little bit wrong. The 5.08 mm grid, where the connectors are being mounted is fixed by the standard. Also the clearance between components and the nex board.What I'm doing is segmenting the backplane into pieces. The standard only specifys one-piece backplanes, so I'm transfering the dimensions for frontplates to my segmented backplane. The standard tells me to have 0.3mm of space between frontplates. What I'm basically asking is: How much space should I put between PCB backplane elements, so they fit nicely besides each other. This clearance is not changing the position of the connector mounting hole, but being subtracted from the width of the segments.I think I'm going with these dimensions:0.5 mm feels right to me. (If I set my caliper to that pitch)±0.2mm is JLC PCB's routing precision, so I'll add that as a worst-case scenario.0.5 mm +0.2 mm = 0.7 mm