Anyone have any experience with 4pcb or know of a good and cheap pcb fab that can do 20"+ boards. My only issues with 4pcb is that for 4 layers the cost increase two-fold. The other 2 layers are simply power and ground with absolutely no routing except for vias which are not blind or buried. While I can do without the inner two power planes it sure makes it easier to route and the circuit is more stable. The fabrication is only slightly more complex than 2 layers so I don't see the need to pay twice as much.
4pcb is quoting me about 25$ a board for 4 for 2-layer 20"x15". I do not need any special techniques except somewhat small traces of approximately 8mils and small holes of around 13mil/25mil. I do need at least 2oz copper but the more the better. 4pcb does not charge any more for 4oz over 1/2oz.
4-layer PCBs at best are made with a 2-sided "on top", then a zero-sided (for insulation), then a 2-sided "on bottom"; there are other combinations to get the same effect - but 3 boards is a minimum requirement. Each etched board, whether it is "busy" as a doily or no traces at all goes thru the same processing steps and thus charge for time and materials at a standard rate -->for the process
It shouldn't cost twice as much The inner planes are virtually solid except through stand-off from PTH. These can be done very quickly using very cheap methods. Since there are no burried, micro, or blind vias it does not require much more processing.
Think about it this way. 1 board costs 350$, 25 boards 500, and 50 boards 700. This is for 2-layer. 4-layer is essentially 2x2layer so by getting 4 layers I have increased the number of boards by a factor of
So, if I ordered 25 2-layers then 25 4 layers(which is 50 2-layers) would cost around 700. Add the addition cost of the prepregs and copper and the pressing process, you might get 800.. but not 1000.
I do realize that it is almost two seperate processes but for the most part it is no different than doing 50 2-layer boards. The plane layers only need to have a drop of resist put where the PTH would be. 2 double sided boards could be used and only an inner prepreg would be needed. The additional costs would simply be the inner prepreg layer, the drop of resist(Which would depend on the number of holes but would be insignificant) and the short time to press all the boards together. Of course one could just require the need for 2 photomasks but they are not expensive either.
Since virtually everything is automated it is not double the cost. You are simply paying for a setup fee, the cost of the material, and their markup. It's easy for them to mark up double the cost on 4-layers because they can claim exactly what you have said... even though it is not true.
The point is that it is definitely not double the cost. It should at least scale down inversely with the number of boards in addition to what it already scales down as(so it might start out double in very small quantities). Of course this is actually how it works as 20+- layer boards, such as motherboards would cost 20x as much as single layers and would not be as cheap as they are. E.G., if it cost 5 to make a single layer then it would cost 100$ to make a 20 layer board... that doesn't include the components. You can get motherboards for 30$ easily.
In fact I have known people who get 2-layer, in small quantities, and convert them to 4-layer. They split the board in 2, put a 2-layer board inbetween. They predrill the copper out where the PTH(which in thsi case they are not plated) so the plane layers do not make electrical contact. This is actually quite easy as they just use the 2- layer board as a template then countersink the holes to widen them. Then they glue and press them together and use wire's for the vias. Obviously this isn't a good way for quality boards or for many PTH's but seems to work well for simple boards that require large inner planes.
Don't get me wrong, I do understand there are additional costs. I disagree with you that in all cases it must be at least double that of
This is really simple. If you do not like that vendors prices shop around. If you can't beat the prices the first vendor offers, do what you will. Where is the beef?
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