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I have a board I'm working on with a coworker; we are debating whether to go 4-layer or 6-layer board, and would like to use 6-layer but haven't found a reasonably priced fab house.

Is there any reputable PCB fab house out there that has good pricing on small-quantity (3-10 pcs) 6-layer PCBs? (approx 5"x6", nothing fancy) The best we've been able to do is about US$700, whereas there are specials on 2- or 4-layer PCBs that are in the $200-$300 range.


clarify background info: the board has 3 widely-used nets = AGND, DGND, +5V, which basically spells 5 layers, and there doesn't seem to be much advantage to 5 vs. 6. We've looked at sharing the AGND and +5V layers, that's an option; we've looked at routing the +5V by hand, that's an option; we've looked at combining AGND and DGND nets and living with the noise. The right thing to do from an engineering standpoint is a 6-layer board, but if it's going to be 2x the price it may be cost prohibitive given our particular situation (further details are beyond the scope of this forum).


clarification: (the board was made last year for $$$, but the question is still valid)

I asked about 6 layers and I meant 6 layers. The background info is only for educational purposes. As far as cost tradeoff judgement goes, here's where I was coming from:

For a shop that is interested in high-volume ultra-low-cost, you can either spend more time to design a 4-layer board well because of layout constraints, or rush through a 4-layer board design and hope it works.

Same thing for a hobbyist without much money wanting low quantities.

For a shop that is interested in time-to-market, you can either spend the money and use a 6-layer board, or rush through a 4-layer board design and hope it works.

We were in the middle, and had a coworker who was leaving, so I had to go with something that worked; we didn't have time to respin. Cost turned out to be not as much a barrier as I thought, but in some situations I get flak from management when cost is high, and it's really helpful to have a modest price option so I don't have to deal with that.

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6-layer PCB - nothing fancy! –  Toby Jaffey Jul 28 '10 at 21:19
    
I thought the same thing, but have been helping a lot of professors get board orders in recently, so I think I could almost quote what specs he means. –  Kortuk Jul 29 '10 at 5:08
    
Another list of PCB fabs: electronics.stackexchange.com/questions/1893/… –  davidcary Mar 2 '11 at 19:37
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Sounds like you have some layout issues - your AGND and DGND layers shouldn't be overlapping (they'll couple together), so you shouldn't need separate planes for the two. –  Connor Wolf May 20 '11 at 2:01
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13 Answers

in my experience having truly separate AGND and DGND nets almost never works out well in practice. 90% of the designs i see that try to do this end up with current loops that introduce EMI issues and can generate more noise in the analog portions of the circuit than using a single ground with careful part placement would.

Having two GND planes also creates a problem for routing in that signals referenced to a particular ground should only ever be run on layers that are adjacent to this plane or its associate power plane. This can result is a pretty funky stack up that can limit where you can run traces. Your best answer would be AGND,signal,?GND,POWER,signal,DGND but thats funky to layout, uses lots of vias, only gives 2 signal layers to route on.

What i would recommend is a single solid ground plane and careful part placement. High speed digital signals and noise will follow the path of least inductance to ground not the path of least resistance. The path of least inductance is the smallest loop area, for signals this is directly under the trace on the adjacent ground plane. In some cases a ground pour on top, bottom, or both can be helpful in reducing noise pick up as well. This is dependent on the components and the design layout.

Create virtual partitions, keep out areas, where you only run either analog or digital signals, keeping in mind that the return current path for the low frequency analog signals is the path of least resistance, while the return path for the high speed digital signals is the path of least inductance. As long as your careful to ensure that the return current paths don't cross, especially a digital return running under your analog sections. You shouldn't get much noise pick up at all.

If your have a particular device that is very sensitive to noise, such as a high resolution ADC, you can use a ground island to increase noise immunity, like this: alt text

In cases where i have some sensitive analog circuitry i will usually also use a power island that is separated from the digital power supply by an LC filter of some sort, depending on the digital frequencies i'm wishing to block.

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Wow. I really like this response. It positively EXUDES experience and trustworthiness. I sincerely hope I'm in a position to hire you someday. –  AngryEE Sep 23 '10 at 1:15
    
I understand your response, but like most electrical design rules, there are cases where they do not hold up. I think this works well in most cases, but there are also many cases where you need the separation. –  Kortuk Sep 24 '10 at 14:12
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I just received an email from e-Teknet about 2,4,6 and 8 layer promotions they are having.

The 6 layer boards are $79.99 each plus shipping, and the proto specials are a 4 board minimum. The specs are:

Maximum board size 35 square inches for 2-layer board, 30 square inches for multilayer boards. Less than 10" in either X or Y direction. 0.062" thick board (FR4 material), 1 oz copper, minimum conductor width/ space >= 7 mil, , minimum annular ring >= 7 mil, minimum hole size >=12 mil (plated through). Non plated through holes are allowed. Board size>1"x1". Tin-lead HAL reflow and green LPI, white silkscreen for both top and bottom sides. For promotions, the boards should have no countersinks, no cutouts and no panels and V-scores.

I have not ordered from e-Teknit but the salesman, Neil Munzinger, has been very responsive to my various queries. They also offer assembly services.

Neil Munzinger

Account Executive

P: 480-752-7854

F: 480-752-7855 E-mail: sales@e-teknet.com www.e-teknet.com

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I just emailed their sales department, because, while I don't have a board ready, I expect to require one soon, and I didn't want the promo to expire. I received the following reply: "The promotion pricing does not end it is ongoing. Juts part of our pricing structure. Thank you and let us know when your ready." Looks like a different definition of "promotion", but that's fine by me! –  Kevin Vermeer Sep 24 '10 at 16:12
    
That could be my mistake as well. I may have have misread the original email. If you end up ordering boards from e-teknit please post about your experience (quality, service, etc). –  jluciani Sep 27 '10 at 14:23
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Others have stepped around the same point, but if you are worried about cost you should really consider going with 4 layers. 4pcb is pretty reasonable for 4 layer boards.

I have found that people tend to think that more layers will result in a better board. This is not always the case. Don't let poor routing be ignored by going with more layers.

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We normally see eye to eye kellenjb, but on this I will have to side with jason. Every answer I have seem him make is very sound quality EE advice. I have a feeling he needs 6 for a nice layout, and 4 is just cutting by. –  Kortuk Jul 29 '10 at 5:10
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going to 6 layers to make routing easier isn't going to do much for your signal integrity. Going to 6 layers because a 4-layer routing cuts up your power planes and makes them ineffective as supply planes is something quite different. –  akohlsmith Jul 29 '10 at 13:54
    
I actually didn't take into consideration who was asking the question. I based my answer off of past experience with evaluating other people's layouts. –  Kellenjb Jul 30 '10 at 1:48
    
@Andrew, when i say making routing easier, I am including avoidance of embedded traces in ground/power planes and a number of EMC considerations. –  Kortuk Sep 24 '10 at 14:35
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Interesting problem. There isn't a "hobbyist" market for 6-layer, so the low-end fabs won't touch this, and high-end fabs charge their usual bucket-of-money NRE. Most people making 6-layer are at companies with the budget to prototype as needed.

Now, you should understand that this is essentially the same things as making three thin 2-layer boards that are then laminated together-- there is a reason that this is more expensive. Rather than generating just 1-2 photoplots for the copper there are 6, and three times the processing time for many of the steps... and three times the potential for goofs that require them to redo the whole board. Because errors are more likely, some fabs include electrical testing with 6-layer, which also contributes to the cost.

Looking around, pcbfabexpress can get you started around $500, but my experience is that you probably won't do much better, for domestic (US) at least. Overseas fabs should cost considerably less, and may be a better option for this sort of thing.

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I recommend Sunstone for this kind of work. I'm not affiliated with them, other than being a very happy customer. I've used a few board houses through the years, but these guys come out on top. Their rates are reasonable, they can accept Eagle board files directly, and every time I've contacted them they've been fast, friendly and efficient. I can't say enough good about them, these guys are on the money.

I just got back a set of boards (6 layer, .005 trace/space, .01 vias) -- I don't think you'll find a board like that for under $700 in small volumes. The trick is to panelize your boards and make an order for 2 panels with 5 boards each. You'll still be paying $700 but at least you'll have a lower per-board cost.

I just saw this link on hackaday: BatchPCB.com will get you cheaper boards if you're willing to wait a little. I've never used their service, and it's only up to 4-layers, but I'm throwing this out there for others to see as well.

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Could you elaborate a little more on this trick? It sounds good. –  pingswept Jul 29 '10 at 0:44
    
You have a single 4x3 board, for example. Instead of ordering two of these boards, you use panelization software (I prefer the Python script called gerbmerge) to make a panel of these boards. Board houses do this anyway, and my experience is that making a 3x4 board is only marginally cheaper than making a 10x14 panel of the same boards. (in my case it cost me $100 more to get 4x the boards out of my last order). When I do this also order the boards tab-routed so they're easy to cut apart. –  akohlsmith Jul 29 '10 at 1:34
    
"You'll still be paying $700 but at least you'll have a lower per-board cost." The board houses already do that to some degree; the difference in total cost between 5 boards and 10 boards might be only $50-$100. –  Jason S Jul 29 '10 at 13:16
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This works, unless your board house doesn't allow panelized boards, or charges extra for it (I'm looking at you, 4PCB). –  Connor Wolf Jul 30 '10 at 0:28
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Board houses that try to play dirty poker by saying my panel is "not a board" or that it's several boards don't get my business, plain and simple. I am asking them for some square footage of FR4 with copper layers, silkscreen and holes. Nothing more. (well electrical test and so on is good too, but the point is that if they want to charge by the board instead of by the panel, they should make it clear. I won't be doing business with them if they do, however.) –  akohlsmith Jul 30 '10 at 16:37
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PCBfabexpress is fairly cheap for 4 and 6 layer boards.

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cool, thx for the suggestion. –  Jason S Oct 25 '10 at 0:29
    
@scottMurphy, can you add more detail, this is currently only a comment. –  Kortuk Mar 22 '12 at 9:18
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I just sent a 4-layer board with some particularly small vias and fine pitch traces out for quote yesterday, and the winner was protoexpress.com. I've previously gotten special discounts from pcbexpress.com, but they don't appear to have any promotions running right now. I suspect you'll have trouble doing better than a 5-day turn for $650 or so.

Oh, one other thought-- try apcircuits.com in Alberta, Canada.

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Don't bother with APCircuits for anything other than 2-layer; they farm out their multilayer stuff to various US houses. –  akohlsmith Jul 28 '10 at 23:12
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http://www.pcbtrain.com will do 10 boards, 125mm x 150mm for £63.40 each ($101).

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Here are a couple of low priced options I've used before (though not for 6 layers).

PCB Universe (pcbuniverse.com) offers a deal similar to E-teknet - 4 pcs/99.99 each (but they provide the option of ordering more than 4 pcs at a discounted cost). Min cost = $400.00.

International Circuits (internationalcircuits.com) they provide a more unique service (fit as many pcs into preset panel sizes):

100 square inches for $350.00
200 square inches for $400.00

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+1, thanks...... –  Jason S Oct 25 '10 at 0:28
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You might want to browse through the list of PCB Manufacturers. Many of them have online calculators that will give you the cost of your board in a few minutes of typing in #layers, minimum trace/space, etc. Crank through a few of them and pick the best one.

"we've looked at combining AGND and DGND nets and living with the noise."

No matter what you do, you will have to live with some noise.

However, do you realize that keeping AGND and DGND separate causes more noise than a single GND plane?

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Everyone seems to say this. Most links show a ground plane that has been split in half and then had traces routed between it. This is not true. If you have an entire layer for Agnd and all associated traces routed with it you do not have increased noise. This is miss-information, that makes sense, but not when you have completely isolated layers. Do not split a ground layer in half, honestly, I do not consider it a good idea, but having a AGND layer and a DGND layer, that is different. –  Kortuk Sep 24 '10 at 14:46
    
I agree that a single copper layer divided into two regions, as in the experiments reported in the articles I linked to, is different from two independent copper layers, each one more-or-less covering the entire board, as described by the original poster. I am curious -- has anyone ever done an experiment showing whether having completely isolated AGND and DGND layers is better, worse, or about the same as an identical board with a single GND layer? –  davidcary Sep 25 '10 at 3:50
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SpiritCircuits sell 6 layer fabrication on their ebay store:

http://stores.ebay.co.uk/Spirit-Electronics/_i.html?_nkw=printed&submit=Search&_sid=429897585

Your order in multiples of 1 sq foot (approx 30cm x 30cm), at £45 per square foot. If your board is smaller than 1 sq foot, they'll panelise it and route to individual circuits for free (but only one design is allowed per square foot).

I'm not sure, but they may only deliver to the UK - you can always ask them.

I've recently ordered a couple of 2 layer boards from them, the service has been very good and the boards look good.

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I have a tendency to only buy American for prototypes because I believe you get what you pay for.. So far, I have purchased from various PCB Fab companies and their are two that come to mine when dealing with "Made in USA" PCB companies.

-Custom Circuit Boards (Link: http://www.customcircuitboards.com/) -Sunstone, like mentioned above (Link:http://www.sunstone.com/)

Both have always produced quality boards ONTIME!

Best of luck.

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You can choose a fab house in Asia with low price ,if the lead time isn't urgent. even plus shipping cost, The board manufactured in Asia will be lower than local factory.I Would like to give you a quote as below

For the 6 layers sample 10 pcs, (FR-4.1.6T,HASL) , Unit price:USD 47.9 ,The total cost will be USD 479 plus shipping cost by Fedex Lead time:10 Days.Transit time:3 days

you can contact Nancy via:5dpcbsales1@gmail.com for more info www.5dpcb.com

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