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Old 5th Jun 2017, 2:53 pm   #21
David G4EBT
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Default Re: More homebrew computerless PCB progress

Some useful info here on all aspects of PCB making:

http://www.electricstuff.co.uk/pcbs.html

Several free PCB CAD packages here:

http://www.electroschematics.com/224...sign-software/

I'd reiterate that most PCB CAD software is designed for automated professional manufacturing processes - not for DIY processes for which it isn't especially well suited. In particular, narrow tracks will be undercut during etching, and small pads will risk being obliterated during the drilling process. Wherever possible it's best to leave as much copper on the board as can be achieved as that speeds up etching and reduces the risk of undercutting of tracks and pads. It makes no sense to have tracks just 1mm wide if there is space to widen them to 2 or 3mm, or to have 2mm diameter pads when they can be 4mm.

To reduce the risk of skidding of the drill bit, it's best to make sure that there is a clearly defined hole about 0.6mm diameter on the pads so that when the board is etched, the hole will act as a guide for the bit when drilling. That's especially so if using HSS drills which flex and 'whip' slightly at the tip, even if set well into the chuck. Carbide drills don't flex, last longer, but snap like carrots if caution isn't used. They've also got larger diameter shanks than will fit in a PCB drill, but if anyone wishes to use a standard pillar drill, (not a good idea, but if needs must...), they'll fit into the chuck.

I sometimes make projects from magazine articles (EPE etc) and when using their PCB artwork to create a mask, I always beef up the tracks and pads using MS Paint. As an example, the attached pic is of a PCB for an EPE 'Active Antenna' project from years ago, which had needlessly thin tracks and small pads, which I beefed up and made the holes in the pads more clearly defined, as shown.

A small PCB drill, drill speed controller (easy homebrew project) and good quality drill stand (ie, definitely not Dremel), minimises the risk of slip-ups when drilling. By the drilling stage, already a lot of time has been invested in creating the artwork, making the mask, exposing, developing and etching the board, so one slip at the drilling stage writes off all that time and effort. Most small hobby drills - Dremels and their clones, run at 10,000 - 30,000 RPM - way to fast for PCB drilling.

Of course, if a board is wrecked, it's only the time that's been wasted and a small amount of PCB material, so it can be done again, (and again), but it's borderline OCD to do the same thing over and over again, and to expect a different outcome. Might just as well mackle something up on strip-board and be done with it.

Have fun - every success in your endeavours.
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Old 5th Jun 2017, 3:50 pm   #22
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Default Re: More homebrew computerless PCB progress

If you're a glutton for punishment and are using FR2 board, you can always use an archimedes drill for PCBs. No skidding, dead accurate.

However, cramp.
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Old 5th Jun 2017, 6:10 pm   #23
David G4EBT
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Default Re: More homebrew computerless PCB progress

Quote:
Originally Posted by MrBungle View Post
If you're a glutton for punishment and are using FR2 board, you can always use an archimedes drill for PCBs. No skidding, dead accurate.
I often use an Archimedes drill for enlarging holes that won't take some component leads.

I tend to just drill all holes 0.7mm, but that's not large enough for things like 1N4007 diodes of 3-legged voltage regulators so I open them up with the Archimedes drill.

Re FR2 board, 'FR' stands for fire retardant. An explanation of the various grades of PCB laminates might (or might not!), be of interest:

FR2 (and FR1) is phenolic resin and hard paper, both of which are hygroscopic (absorb moisture). The material is obsolete and isn't produced or used anymore commercially, but can still be found cheaply from e-bay sellers. Also, phenolic resins emit small amounts of phenol and formaldehyde and pose a health risk, but even so, I like the aroma!

FR3 = Epoxy resin + hard paper. It looks similar to FR2 but doesn't use phenolic resin.
It tends to be used in budget-priced consumer electronics.

FR4 is epoxy resin + glass fibre fabric: This is the most commonly used material in the fabrication of single and multi-layer PCBs.
It's RoHS/WEEE compliant and has near zero moisture absorption:

https://en.wikipedia.org/wiki/FR-4

FR5 = Epoxy resin + thermostable glass fibre fabric which can tolerate higher operating temperatures.

For the likes of us, really, it's a choice between FR2 & FR4.

I only use FR2 for things like front panels for projects instead of say aluminium sheet, and it does have the merit of being easy to drill and file, but I never use it for PCBs, for which I always use FR4 due to FR2 being hygroscopic.

Some might say: "Well if it's only being used indoors in dry conditions, it doesn't matter that FR2 is hygroscopic". Not so - it does matter. Indoors is not 'dry' in terms of relative humidity (RH), which is the most common measure of humidity. It's a measure of how close the air is to being saturated - that is how much water vapour there is in the air compared to how much there could be at that temperature for it to be fully saturated.

Average annual relative humidity outdoors in the UK ranges from 70% (low) to 90% (high) and varies little in different parts of the country:

Source: https://www.currentresults.com/Weath...ity-annual.php

Surprisingly perhaps, typical indoor relative humidity levels in centrally-heated and well ventilated UK domestic properties ranges from 50– 55%, much higher than we might imagine.

Source: http://www.telegraph.co.uk/finance/p...or-a-home.html

So that explains why paper caps break down over time due to the absorbtion of moisture, and why - over time - FR2 PCB resin/paper substrate (commonly known in yesteryear as 'SRBP' - synthetic resin-bonded paper) ceases to be an insulator and morphs into being a resistor and it's why it's long since not been used in the commercial manufacturing of PCBs.

False economy IMHO when FR4 is cheap enough on e-bay.
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Old 5th Jun 2017, 6:35 pm   #24
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Default Re: More homebrew computerless PCB progress

There's also -- or there used to be, when I worked in the industry -- CEM-1; a single-sided laminate which we used for things like boiler controls. It was sort of intermediate grade between FR2 (cheap, nasty SRBP, not recommended for mains) and FR4 (glass fibre, also available double-sided). There may also have been a CEM-3, but I don't remember clearly enough to say for sure.
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Old 5th Jun 2017, 8:37 pm   #25
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Default Re: More homebrew computerless PCB progress

Have to agree that FR2 smells nice
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Old 8th Jul 2017, 9:18 pm   #26
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Default Re: More homebrew computerless PCB progress

Quote:
Originally Posted by MrBungle View Post
If you're a glutton for punishment and are using FR2 board, you can always use an archimedes drill for PCBs. No skidding, dead accurate.

However, cramp.
Mr B in my younger days ( possibly out of inexperience/exuberance and enthusiasm) ,I found a motor from a well known office equipment recording equipment with the innards of a "chocolate" drop 2A connector used to connect the drill to the motor ,with a push switch in the circuit, worked well. Motor was 12-18v, but it did the job, powered from a rectified output from my Weller. Trick was not to use too much force.
As I've mentioned in another post, I noticed Aldi selling a small cordless ,which might be better suited for PCB work than the normal sized cordless.
However, I saw someone mention not to use drills in drill stands. Strangely enough way back in the Stone ages ( or so it seems now), I did a stint at Dollis Hill, and we used these to drill our one off PCB. no dramas or problems, just a neat driled PCB.
Julie- strangely enough, cleaning out a cupboard, I came across a bit of double sided I "WON" in my days at GEC. This was a bit of board that hadn't developed properly ,and it was cheaper to sling it ( or sell it off), than rework it.

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Old 8th Jul 2017, 10:51 pm   #27
David G4EBT
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Default Re: More homebrew computerless PCB progress

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However, I saw someone mention not to use drills in drill stands.
Really? That sounds like a very odd thing for anyone to have said. I wonder what flawed logic they relied upon to make that assertion?

Drilling a PCB calls for pinpoint precision, especially if the layout has been created in one of the many CAD packages which create thin tracks and small pads, really meant for commercial CNC production - not homebrew. The more holes to be drilled in a PCB, the greater the risk of the drill skidding and spoiling - if not wrecking, the board. By that stage, the board has been exposed, developed, etched, many holes drilled, then ooops, one slip of the drill bit and it's curtains.

Just to illustrate what can happen, below is a PCB of a drill speed controller I designed. (The second pic shows it in use, with a Minicraft drill and stand).

That said, there are some poor quality drill stands around, not least of which seems to be the Dremel one as there is too much play in it from what I've seen.

I'd drilled the holes in the PCB with the Minicraft drill and drill stand, using a new 0.7mm HSS drill bit, which I only use for one PCB then discard as they're not expensive. I use a magnifying lamp to make sure I place the bit with precision for each hole to be drilled. You'll see how cleanly and accurately the holes are drilled - not throwing up any burrs, as the drill is in an out in a couple of seconds.

But look at the misplaced hole in the pad at the top left - the last of 53 holes! That happened because I hadn't marked a large enough hole in the mask to help centre the drill for that pad, so a hole to aid drill placement wasn't etched. I could, and should, have just centre punched it, and a little voice in my head told me that as I drilled it, but I went right ahead and drilled it anyway. The bit skidded slightly, and in this instance didn't cause a problem, but suppose it had been one of the 8-pin DIL I.C. pads? It could easily have wrecked the PCB after considerable time already expended, apart from blunted pride. I'm almost ashamed to post the pic, but that's my penance for being slapdash and I've promised the little voice in my head to not do it again.

I've seen countless youtube videos of guys holding a PCB in one hand and a 'Dremel' style drill, or an even larger electric drill in the other, but to be brutally honest I think that's very much at the 'bodgertronics' end of the hobby. It's their time - not mine, they're not breaking any laws, not causing any harm, and I'm sure won't take any lectures from the likes of me. They'll do it their way - I'll keep bimbling on doing it my way.

Apologies if I'm making a nuisance of myself.
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Old 8th Jul 2017, 11:36 pm   #28
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Default Re: More homebrew computerless PCB progress

If it's any consolation, all of my holes look like that Dremel stands for you!

More seriously, I've decided to skip this problem entirely my using surface mount components. Well, surface mounting normal components to start with. I built another RF probe and just surface mounted everything as I managed to snap my last 0.7mm drill (in a rubbish Dremel stand - it's going on eBay next week!). This then lead to the purchase of some 1206 resistors and a few Schottky dual diodes in SOT23, and some 1206 sized C0G capacitors. Then I was pleasantly surprised at how cheap the SA612AN's are in SOIC from RS and the price of varactors. Then I discovered chip inductors. So an hour or two after Parcel Force crammed the Jiffy bag through the letter box when I was in I had a working and rather quite stable SMD VFO floating at 7.030KHz. The thing is half an inch down each side! Drift is 100Hz/min for the first 5 mins and then 10Hz a min. Blasting it with a hair dryer only causes 50Hz drift or so as well (when inside an aluminium project box) and it recovers quickly. Very impressed!

I've too busy to take it any further for a while unfortunately though due to work. I haven't even fired up the soldering iron for a week and a half.
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