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Backplane Take 1

A project log for Retro rack and backplane computer

Old style modular system for development of retro computers

Hacker404Hacker404 04/07/2017 at 09:086 Comments

Well here is what went wrong (in pictures) -

Above: Plain printout using color LASER printer.

Above: Dirty FR4 roughly cut to oversize.

Above: Cleaned

Above: Dextrin sheet made by Pulsar - This is the *good* sauce, you get 100% toner transfer every time

Above: Dextrin that has been printed on

Above: Dextrin taped to leading edge of board for fusing

Above:Toner fused to FR4 by laminator

Above: Toner Reactive Foil (Green TRF). The is the *secret* sauce. It will get you down to 5 mil traces when you get the other things right as well.

Above: TRF ready for fusing with laminator

Above: You can see the traces fused.

Above: I missed it! The green diagonal line on the fourth socket position from the right that you can see on the Toner Reactive Foil. Explained later.

Above: I missed it again, that same line after etching.

Ok, The problem wasn't the beer lol. I am drinking that now - not when I was doing the board.

A number of things went wrong and here they are -

1) I used 10 mill traces when there was room for 15 mill traces. I wanted to fix this in the CAD but there was no way to edit trace widths except for one segment of one trace at a time. This shouldn't have been a problem BUT it added to other issues. I have made PCB this way down to 7 mill traces.

2) The diagonal line mentioned in the pictures above was a clue that I missed. The printer I used has a tear in the fuser film sleeve and that more or less destroyed the quality of the end product.

3) This board won't fit into my etch bowl. I left it elevated at on end and used a brush to brush on the etch. This really doesn't work for the etch I use as it needs to be kept at 70 C which doesn't happen when one end of the board is in free air. As a result the board is over etched in the middle and under etched on the ends.

I didn't have a good look at the board yet but it's probably unusable. I will have to come up with a plan 'B' or try to find a lager etch bowl or make the board in two halves. And either fix that printer or try or buy another.

Anyway, I will worry about that another day.

Discussions

K.C. Lee wrote 04/08/2017 at 09:12 point

If you are using eagle cad, you can change trace width of selected group.

Think you have it tough with delivery?  5 weeks is so much faster than I can get  these day in Canada.  When I order stuff from China with free shipping, it can take up to 2.5 months - most of it is because it sits in Canada Customs for anything other than first class mail.  Anything over $20, I get nailed having to pay duty plus heavy processing fees that is more than duty.

Last year when I order OSH park from US with first class USPS, it sat at the UPS depot for more than 1 month before it was handed over to the postal system.

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Hacker404 wrote 04/08/2017 at 10:04 point

Man! that is bad. I have heard others talk about how hard it is in Canada. Hopefully that will become less of a problem as time goes on as international consumer trade can't stopped and it will become too hard for governments to manage even to get some 'cut' of the money. 

For me the US is the last place I order from. I can't get anything out of the US for less than $50 to $70 shipping. 

I order mostly from China / Taiwan / South Korea which is fine for a lot of things but the US has for a long time been a leading manufacturer of silicon technology. It's a shame that with all the skills the US has, I have to treat them as a 'last resort' because of their highly expensive transport costs.

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K.C. Lee wrote 04/08/2017 at 10:44 point

The trend has gone worst over the last 2 years actually.  2 years ago, it took 3 weeks, then that became 4 and went up to 1.5 months last Oct.  Now it is 2.5 months. Most of that is in a warehouse at customs.  The postal system used to scan everything before that and they have gone out of their way to remove any tracking in their system.  It used to be $40 limit, but the lobbying got it slashed to $20 and that was before the millennials were born and was never adjusted. The government actually loses money for collecting duties/sales tax that low.

Ordering from US based digikey is actually pretty good with next day delivery and hassle free with prepaid sales taxes, but they are the only few that offers such sweet deals.  Stuff from China have improved over the last 4-5 years to the point I had sourced entire project parts. I order lot of stuff from China, but the 2.5 months is a bit too much and pretty much kills any HaD contest time frames.

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Vince Hodges wrote 04/08/2017 at 12:32 point

If you're near the border, there are companies that offer a US delivery address for a small fee ($5 for the one I use) - usually a lot less than shipping to Canada.  Might be quicker too.  I've never had to pay (on US made goods mind you) duties or even taxes.

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Hacker404 wrote 04/08/2017 at 08:30 point

I may be able to get to two layers if I can buy large enough double sided FR4. 

Unfortunately, when it comes to getting boards made, I might as well be on the moon. I am in *wrong* part of the *wrong* hemisphere. It would take 5 weeks to get a board here at the lower costs and even they are upwards of $80 plus postage for a board this size. If I though the back-plane in the bin (and I probably will) then it's cost me a measly $10 and an hour or so of time. 

A PCB house would be good when I have ironed out any issues but if I *start* with a PCB house then I am going to be dead before I can finish this. 

Thanks for you comment all the same and I hope I can manage without starting with PCB fab, otherwise I will just be proving you right.

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Yann Guidon / YGDES wrote 04/07/2017 at 19:14 point

I'm sorry mate :-(

This kind of board needs (at least) 2 layers of PCB, you'll save money and time by going to a professional fab :-/

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