Prometheus for Rapid Prototyping - Forget Everything You Know About PCB Milling

[rocco]

The problem is that sadly PCB milling has been sold for a long time, with a lot of hype and its failed to deliver for many folks.     But your asking me to forget that.   So i'm assuming that this system does something different and will deliver something that the others cant.        So far, we know that it might be useful for some RF designs,  but I can't see any use-cases for anything else yet.

Ok, I see. That's not what I'm asking you to forget... it's not that Prometheus does anything that no other system can't, it's that it does what professional systems do for a significantly lower retail price. I'm asking you to forget how expensive professional PCB milling machines have to be. Or put another way, nothing near it's price (AFAIK) can do what it can do as fast as it can do it. That's all that I meant by the "Forget..." phrase. The big disconnect in price between every other professional machine and Prometheus is what's new.

Maybe I could say "forget having to spend $8,000 to get professional results from a PCB mill, where "professional" means sub-6-mil trace/space with a spindle greater than 30,000 RPM and forget spending $2,000 on a machine that doesn't give you professional results". That's too many characters to fit that into the title though. Yes, the title is advertise-y - I'm not asking everyone to literally forget everything about milling - I thought that would be obvious, and I elaborated on all this price/performance stuff in the first post that explained what's different.

You mentioned that you were sold on the idea of a PCB mill by a sales rep who promised something and the machine didn't deliver. I'm curious, could you tell me what kind of work you intended to do on you machine that made you disappointed (if it's not confidential)?

[mrpackethead]

Ok, I see. That's not what I'm asking you to forget...

" Forget everything you know "...  You asked me to forget everything i know...   



I'd still like to know what use-cases you think that PCB Milling provides a positive return on.   *on any platform) Other than RF, i'm not seeing one.      I woudl have thought this woudl have been quite a fundemental part of any strategy to sell it.   Other wise its a solution lookign for a problem..  I'd really like to know what problems its trying to solve.

[nctnico]

I'd still like to know what use-cases you think that PCB Milling provides a positive return on.   *on any platform) Other than RF, i'm not seeing one.      I woudl have thought this woudl have been quite a fundemental part of any strategy to sell it.   Other wise its a solution lookign for a problem..  I'd really like to know what problems its trying to solve.

I can imagine lots of customers for a PCB mill are just set in their ways and in their mind & workflow they require extremely quick prototypes. Messing with chemicals is usually surrounded by all kinds of environmental regulations so for a company it might be cheaper to buy a PCB mill compared to investing into a workspace where people can etch boards and have someone monitoring health & safety yadda yadda yadda.

[mikeselectricstuff]

I actually think the strapline is well-chosen - if it had been "forget all you know about in-house PCB production" that would certainly have been over the top.

What most people know/believe about PCB production is that LPKF machines are over-promised, expensive and often troublesome. Considering how long they've been in the business it's surprising they've not produced anything better/cheaper. These days they seem to be focussing more on expensive high-end lasers for stencils and PCBs.

If this machine can reliably and consistently do 5 mil track/space with minimal babysitting then I have no doubt that some people will find it genuinely useful, and undoubtedly more useful than an expensive, over-sold machine with poor software. As has been mentioned, LPKF have ruined the reputation of milling for some people.
Time will tell if that the resolution spec and good reliability is actually achievable in practice.

IME around 10 mil is the limit for reliable chemical etching using laser printed artwork, and drilling is a PITA. Even if you have a small CNC it's borderline impractical to CNC drill a chemical-etched PCB due to difficulty of alignment and small size errors in the laser-print process.
The mess and hassle factor on chemical etching isn't much an issue if you have room to set up a permanent dedicated space for it.

A couple of questions :
Have you done tests on achievable resolution vs. copper weight ? e.g. do you need to use 0.5 oz copper to get maximum resolution reliably?
What is the running cost in terms of tool usage?

Auto tool change would be a killer feature, especially for the drilling. I wonder if it would be possible to make a chuck that used a combination of friction/magnets for initial hold/release, plus centrifugal force to increase clamp pressure while running. At 50Krpms you potentially have a lot of force without much mass.

[ultrasmurf]

One possible use case, at least theoretically since I sometime wished I have one of those nice PCB milling machine : When doing a repair job, and you found out that one of the EOL chip has given up the ghost, and you could actually fix it with a different chip only that you need to have an adaptor to it. Or even replace the whole board with an implementation of simple microcontroller instead of transistor and IC. Most of repair I'm doing will be "please fix it by yesterday..." so having one tool that can make a simple PCB while im repairing other board will be superb... etching tools sometimes are not practical even for the industry, as some region have a stringent requirement to even have a license to obtain chemical (let alone use it...) and it will be too difficult to meet..

[janoc]

I can imagine lots of customers for a PCB mill are just set in their ways and in their mind & workflow they require extremely quick prototypes. Messing with chemicals is usually surrounded by all kinds of environmental regulations so for a company it might be cheaper to buy a PCB mill compared to investing into a workspace where people can etch boards and have someone monitoring health & safety yadda yadda yadda.

That's probably true, the safety regulations can be crazy, but you don't have the same problem with a workshop equipped with stuff like a milling machine producing fine FR4 dust? At least ferric chloride isn't carcinogenic, FR4 dust is. Other materials' dusts/shavings can be fire/explosion hazards. Then you have the coolants, cutting liquids (that's mostly for machining metal, though) - those need to be properly dealt with, etc.

I would expect that an expensive dust extraction/air filtering setup would be a minimum requirement, but I have never had to comply with these regs. What are the typical rules for these things?

Then there are the usual workplace safety trainings and such, but that likely applies the same whether you are etching or milling. Getting finger burned from the etchant or cut/torn off by a CNC machine is a hazard in either case.

[rocco]

I can imagine lots of customers for a PCB mill are just set in their ways and in their mind & workflow they require extremely quick prototypes. Messing with chemicals is usually surrounded by all kinds of environmental regulations so for a company it might be cheaper to buy a PCB mill compared to investing into a workspace where people can etch boards and have someone monitoring health & safety yadda yadda yadda.

That's probably true, the safety regulations can be crazy, but you don't have the same problem with a workshop equipped with stuff like a milling machine producing fine FR4 dust? At least ferric chloride isn't carcinogenic, FR4 dust is. Other materials' dusts/shavings can be fire/explosion hazards. Then you have the coolants, cutting liquids (that's mostly for machining metal, though) - those need to be properly dealt with, etc.

I would expect that an expensive dust extraction/air filtering setup would be a minimum requirement, but I have never had to comply with these regs. What are the typical rules for these things?

Then there are the usual workplace safety trainings and such, but that likely applies the same whether you are etching or milling. Getting finger burned from the etchant or cut/torn off by a CNC machine is a hazard in either case.

Nctnico's point may explain why universities like this - they don't have to deal with the regulations of chemical etching.

Note that I've found nothing that indicates that FR4 is carcinogenic but if you have a source, please post it - it would be good to know what regulatory body classifies it that way. We can compare the SDS of FR4 copper-clad with ferric chloride (links below). Both substances are, "Not classified or listed as a carcinogen by IARC, ACGIH,
CA Prop 65, or NTP" according to the SDSs by MG Chemicals. On the other hand, we see that ferric chloride causes "serious eye damage" (p. 2) while for FR4 copper-clad it says "Based on available data, the classification criteria are not met".

The exposure limits for the dust are shown on p. 5. For a vacuum/filter, you could choose a ULPA filter over HEPA if want the best in filtration but the extra fraction of a percent difference costs way more. FR4 is no picnic but on paper it looks like ferric chloride gives more to contend with, from a regulatory standpoint.

Section 11: Toxicological Information
FR4
Symptoms Summary
Eyes May cause redness and mild irritation.
Skin May cause mild irritation.
Inhalation May cause nose, throat and lung irritation.
Overexposure to dust or metal fumes may lead to respiratory tract
irrititation.
Ingestion No effect known
Chronic No effect known

Ferric chloride
Symptoms Summary
Eyes Causes burns, severe irritation, redness, or pain.
Skin Causes redness, pain, or brown stain on skin.
Inhalation Inhalation of vapors or mist may cause irritation, coughing, or sore
throat.
Exposure to large doses of hydrogen chloride can cause cough,
labored breathing, and shortness of breath.
Ingestion May cause severe irritation to the mouth, throat, esophagus, and
stomach. In large doses, it may also cause abdominal pain, nausea,
vomiting, diarrhea
Chronic No known effects

Links:
SDS for FR4 copper-clad: http://www.mgchemicals.com/downloads/msds/01%20English%20Can-USA%20SDS/sds-500-series.pdf
SDS for ferric chloride: http://www.mgchemicals.com/downloads/msds/01%20English%20Can-USA%20SDS/sds-415-l.pdf

[tooki]

I still can't fathom why the experts on here can't accept that there is a market for these machines and there has been for decades.

Because many people are incapable of seeing beyond their own needs: if a product isn't a good fit for them, then it's not a good fit for anyone. (Look at the computer and phone platform wars: most of it is simply refusal to accept that a competing platform might be a better fit for someone else.)

[rocco]

A couple of questions :
Have you done tests on achievable resolution vs. copper weight ? e.g. do you need to use 0.5 oz copper to get maximum resolution reliably?
What is the running cost in terms of tool usage?

Auto tool change would be a killer feature, especially for the drilling. I wonder if it would be possible to make a chuck that used a combination of friction/magnets for initial hold/release, plus centrifugal force to increase clamp pressure while running. At 50Krpms you potentially have a lot of force without much mass.

All of my testing has been with 1 oz. copper (FR4 and Rogers). I could imagine 0.5 oz copper yielding even better results since the tool doesn't need to plunge as deep.

Tool cost is the most significant consumable cost. I'm going to offer 3 classes of bits: economy, performance, and accuracy. Economy bits are estimated to retail at $12 each and should do a few boards with them (not many; a few). The disadvantage is that they need to be run slower, around 13 IPM. You can do 8-mil trace/space with them. Performance class bits are 15 degree tapered end mills that can do 4/5 trace/space at high speed. The bit in the video that did the milling was a 7-mil diameter bit of this type, and in the video it's max feedrate was 85 IPM, which is insanely fast for that size tool. These will range from $16 to $19 each depending on size (smaller tend to cost more). With volume, I'll be able to offer these even less, which is really cheap if you shop similar tools on competitor sites. The Accuracy class are standard square end mills (the cutting profile has right-angles; it's not a "V" shape). These cost about the same and are in between economy and performance in terms of speed. They have the shortest life though, so they're offered if you're really crazy about trace consistency. You might just get one or two full-size boards with these before they break. Anything more is a bonus (I mean, if your boards are only 2"x1", then you'll get many more - I'm talking about full-size boards). I imagine the performance class of bits will be much more popular because the are nearly as accurate and last longer and cut faster.

A good estimate for the bit depreciation cost of a double-sided 5"x4" board could be anywhere from $4 to $20, depending on which kinds of bits you choose. This is a rough estimate. Cut the board area in half and same goes for the cost.

An important thing I should mention: the bits are somewhat custom for the current spindle design and they should be purchased from us to work properly, which I know doesn't sound great but the spindle design is a huge part of the reason I can build this tool for thousands of dollars less, so that's one of the compromises I had to make. The bits I'll retail are cheaper than those offered by the other guys by 15% or more anyway, so it shouldn't be a huge drawback for people. However, I am also working on a universal spindle that could accept all types of bits and still have great runout specs (if it passes testing).

[mikeselectricstuff]

the bits are somewhat custom for the current spindle design

But will your spindle take standard carbide PCB drill bits ?

[rocco]

They are carbide, yes. The part that's custom or hard to find is that the depth ring needs to be set at .587" for a standard 1.42" long tool (that's not a big deal). The more difficult spec to meet is that our bits have a shank diameter of .1248" +0/-.0001. Very tight tolerance window. But like I said, they're actually cheaper, probably because I'm ok accepting a lower profit margin on them. I also work directly with US manufacturers.

A universal spindle design is something I'm working on and would like to see. I'm not intentionally trying to lock people into using my bits - it was a compromise I made that enabled me to design a spindle that achieves .0001" Total Indicated Runout and 50,000 RPM max speed, for something not costing $1,000 - $2,000, just for the spindle. At that point, Prometheus would be approaching the price point of the other professional machines on the market and there wouldn't be a point. So that was the compromise.

If anyone knows of a spindle with those specs or better that I could buy off-the-shelf for $150 or less, please, please, please let me know! I'm not being sarcastic - I would gladly put that in there and then as a bonus Prometheus could accept universal bits. I just don't know that anything that cost-effective exists. I've looked and haven't found anything, so I was forced to make my own in order to hit my price target. A typical import spindle with an ER collet will usually yield .003 - .005" of runout. A European manufacturer of a rotary tool quotes that their tool has just .001" of runout (which is 10 times more than Prometheus but at least closer than the others) so I got one but actually measured that it was .003". You can find the right specs for 4 figures; at 3 figures I have had no luck.

[rocco]

Oh sorry - you were asking about drill bits. The same answer applies, but those are significantly cheaper than the end mills.

[mikeselectricstuff]

Oh sorry - you were asking about drill bits. The same answer applies, but those are significantly cheaper than the end mills.

Yes - because you may need quite a few different sizes, so using off-the-shelf bits would be useful. Shaft precision is probably less important as drills should mostly self-guide, and there won't be any lateral force.
Will your system produce enough torque at lower speeds for bigger drill bits- say up to 3mm or so ?

[rocco]

It's still important to be less than or equal to .1248" shank diameter otherwise the current spindle won't accept them. I totally agree it would be useful. Makes my job easier too because I won't have to stock so many parts. That's why I'm hoping the universal spindle design works out. Fortunately, my bit manufacturers are understanding of this and willing to deal in smaller quantities as I get going.

I've tested that 3.175 mm drills work. That's the size that you see in the video that made the first two holes for the alignment pins.

[mrpackethead]

I still can't fathom why the experts on here can't accept that there is a market for these machines and there has been for decades.

Because many people are incapable of seeing beyond their own needs: if a product isn't a good fit for them, then it's not a good fit for anyone. (Look at the computer and phone platform wars: most of it is simply refusal to accept that a competing platform might be a better fit for someone else.)

Despite being asked, and dodging the question the OP has to yet provide some idea of what use-cases this method provides a positive return on.     Its not a question of acceptance. I'm declaring that despite trying ( with considerable money and time ) I can not see a proposition ( other for some corner case RF stuff ) that is better than i can do with getting pcbs made in a more traditional way ( which is resonably quick and fast ).   If this process can be shown to save me time/money ( the two are largely interchangable ) i'd be all over it.    Even if this device was free ( as in $0 ) the full picture economics dont' seem to work for me.    But i'm completely open to seeing how it can work.

[free_electron]

small question. You do through hole . how ?

[rocco]

small question. You do through hole . how ?

When it comes to vias, I've not added anything beyond the known methods - either slip a wire through the hole and solder top and bottom pads, or use rivets made for this purpose. I've personally never used the rivets, but I've heard that other people have had success with them.

Vias are another pain point and one that I'm going to play with. For now, my immediate goal was just to deliver a machine that competes with the professional ones on specs but costs 1/3 or 1/4 the price. Then I'll work on a better via system and ability to add a solder mask (resist, as some call it) as well.

[mikeselectricstuff]

small question. You do through hole . how ?

When it comes to vias, I've not added anything beyond the known methods - either slip a wire through the hole and solder top and bottom pads, or use rivets made for this purpose. I've personally never used the rivets, but I've heard that other people have had success with them.

Rivets are OK but reduce the hole size - fine for vias but less so for through-holes. Can be a little fiddly - need good tweezers.
Snap-off through-linking pins are about the quickest, but they could do with making smaller ones.
The trick for using wires is to bend a wire into a "U" and feed it through 2 holes, solder then  cut off - the U makes it much more stable and easier to solder neatly and stops the other end wiggling about when the second side is soldered.
 
One advantage of a  cnc mill type system over chemical etch is it makes it potentially possible to use the same plating process as 'proper' PCBs, where the holes are drilled first and then plated before patterning. I don't know much about the chemistry involved to know how practical it is to do in-house - I know it involves a catalytic process to make the inner walls conductive, followed by electro-plating.

[m98]

LPKF has a nice product for via plating, the ProConduct paste. Just apply a protective adhesive film before drilling the vias, then after drilling apply the paste with help of some kind of DIY vacuum table contraption and cure it in an oven.

[janoc]

Nctnico's point may explain why universities like this - they don't have to deal with the regulations of chemical etching.

Um ... no. Even universities have to follow the same regulations as industry does. There could be exception for research labs and similar situations but not when they are running a workshop making PCBs (or anything else) for their internal use. The safety rules are the same.

Note that I've found nothing that indicates that FR4 is carcinogenic but if you have a source, please post it - it would be good to know what regulatory body classifies it that way. We can compare the SDS of FR4 copper-clad with ferric chloride (links below). Both substances are, "Not classified or listed as a carcinogen by IARC, ACGIH,

Haven't found the studies, but the FR4 material sheet (http://www.tlm.co.th/download/msdsesd3000.pdf) shows this:

Fibrous Glass: This product contains fibrous glass. Although early studies showed possible links between fibrous glass and cancer,
current research indicates no links between fibrous glass and human cancer. Glass wool, which differs form glass in it morphology,
continues to be evaluated as a possible humancarcinogen. (Group 2B) by the IARC.
OSHA PEL = 5 mg/m3
 (resp); 15 mg/m3
 (total)
ACGIH TLV = 5 mg/m3

and

Machining, grinding or sawing this material may generate harmful dusts. Continuous filament glass fiber is not considered fibrogenic,
however, it is woven from E-Glass fibers which are listed by IARC as "special purpose glass fibers" and designated as "possibility of
carcinogenic in humans." Inhalation of copper fumes, while not expected to occur under typical conditions of use, may cause metal fume
fever.

I think the problem is the production of fine particles that are known to cause human cancers when inhaled in general (similar like particulate air pollution, silicosis, etc.), not necessarily FR4 specifically.

The exposure limits for the dust are shown on p. 5. For a vacuum/filter, you could choose a ULPA filter over HEPA if want the best in filtration but the extra fraction of a percent difference costs way more. FR4 is no picnic but on paper it looks like ferric chloride gives more to contend with, from a regulatory standpoint.

Not sure about that - the FeCL3 health hazards are about the same or smaller than for many domestic cleaning products, where strong acids and hydroxides are common, some even produce chlorine gas (!). So I wouldn't expect some crazy requirements beyond basic safety training, fume exhaustion and proper disposal arrangements being required unless working with it on a huge scale.

The hydrogen chloride part doesn't apply unless you mix hydrochloric acid there, which is not normally done.

[rocco]

Nctnico's point may explain why universities like this - they don't have to deal with the regulations of chemical etching.

Um ... no. Even universities have to follow the same regulations as industry does. There could be exception for research labs and similar situations but not when they are running a workshop making PCBs (or anything else) for their internal use. The safety rules are the same.

I meant that universities may prefer milling because if they're milling (and not etching), then they don't have to deal with regulations regarding chemical etching (because they're not doing it in the first place if they use a PCB mill).

[mrpackethead]

What is this machine useful for.  how could i justify it to my boss.

[janoc]

I meant that universities may prefer milling because if they're milling (and not etching), then they don't have to deal with regulations regarding chemical etching (because they're not doing it in the first place if they use a PCB mill).

Ah okay. I read it as you saying that universities have somehow looser safety/environmental regulations than the industry.

However, what you are saying goes certainly both ways. If the uni has a machine shop then milling is a logical choice. If they have chemistry/biology labs, adding an etching machine for the electronics/robotics/EE department would be a no-brainer but they may not have the trained staff to run and maintain a CNC. Most places I have been to had both kinds of facilities though, including for student use. So this is not really a major issue -  the "mess" is there because of some other department already, so some more doesn't matter much.

[Mechatrommer]

What is this machine useful for.  how could i justify it to my boss.

here again... https://www.eevblog.com/forum/reviews/prometheus-for-rapid-prototyping-forget-everything-you-know-about-pcb-milling/msg1189948/#msg1189948 and nobody is forcing you to justify it to your boss...

i just realized the OP claim 5 mils tolerance, i believe this is highly optimistic value. we need proof for that. in the video already showing inconsistencies in isolation/mill thickness, that i estimate between 0.5mm - 1mm milling. 20 mils (0.5mm) tolerance maybe believable/achievable. my 0.5mm drill bit may break at an instant.

[mrpackethead]

What is this machine useful for.  how could i justify it to my boss.

here again... https://www.eevblog.com/forum/reviews/prometheus-for-rapid-prototyping-forget-everything-you-know-about-pcb-milling/msg1189948/#msg1189948 and nobody is forcing you to justify it to your boss...

No body is. But I'm desperately trying to figure out what the tangible benefits to owning one is.  Because clearly there are people who believe there is.   But as yet, nobodys provided a 'full cycle' story about how it helps.