Cheapest way to get higher density PCBs

[stevenhoneyman]

I'm (still) looking to move from QFN to BGA to be able to fit more stuff in to the same size board. My sticking point at the moment is the price to get the PCBs fabricated. I asked elecrow, and the cost to go to 4mil space/trace for a 4 layer design (from their normal 6mil limit) was $140
If I was making stuff professionally, of course that wouldn't be any issue... but I'm just learning as a hobby/spare time filler so any cost saving measure when I expect to make mistakes is a good thing.

Please could someone more experienced than I am let me know what I should be aiming for to reduce PCB costs for specs to handle a few 0.8mm pitch BGA parts?

For example, what would the expected order of these from lowest to highest cost be?
- 0.3mm vias -> 0.2mm vias
- 6/6 down to 4/4
- filled vias in pads

Or there's the "cheating" options:
- DIY filled vias in pads
- aim for 5/5 and hope it's fabricated OK
- Reduce pad size and make via rings slightly smaller than allowed, so that 6/6 fits

Any 1 of those would be enough (I think), I'd just like a little advice on what to get a quote for and then I'll start on the layout to fit that spec!

[stevenhoneyman]

I should have added - defect rate isn't much of a problem, so out of 10 boards if only 3 were 100% OK, that'd be fine.

[T3sl4co1l]

If your problem is cost, stack a pair of two layer boards.

A four layer board costs, well, basically, twice what a two layer board does, give or take additional labor.

If you need circuitry per dollar, in a limited volume, you'll probably get there better with cheaper stock.  If you must have four (or more) layers for absolute maximum density, well, put your money where your space is(n't).

Tim

[stevenhoneyman]

Thanks. I guess it's the labor cost, because $140 is around ten times the cost of what I'm paying for 2 layer.

There's a site I was playing with that gives (inconsistent) instant quotes for various "higher spec" boards, and that gave me a hint that it is the layer count and not really the drill/track size that adds the huge amount. So I'm possibly thinking I could get away with 2 layers with 0.2mm vias and 4/4 tracks. I'll have to have a try and see if I can get that to look like it should work and then get some accurate quotes.

Failing that, I'll stop being a cheapskate and pay the 140

[T3sl4co1l]

Ya, drill/space is more a matter of "nah, she'll be roit!" versus inspecting things with a pocket loupe and fine-toothed comb.  Normally when you order 10, they make 11-13 and discard the bad ones; their losses go up for finer tolerances, so they have to charge more for more waste.  But it's almost constant labor, until the limitations of their process (printer raster pixel size?) become dominant.

Also, fine drills break easily, or really fine holes have to be laser drilled (pricier equipment? slower?).

Four layer boards take more steps obviously, and have to be lined up precisely (by x-ray, no less), however they're bonded.  (You can make two 'core' boards and laminate them together with one thin 'core' between them, or 'build up' each side, having relatively close top and bottom pairs.  The latter is more common, as it gives reasonable width ~100 ohm traces for high speed work.  The former would be good for extra supply bypass (closer planes = more capacitance, lower impedance supply), or internal routing with supply pours on the outer layers.)

Tim

[printedcircuit]

I'm (still) looking to move from QFN to BGA to be able to fit more stuff in to the same size board.

I would not call it high density PCBs. Your design do not contain via smaller than 1.5mm. and there is no blind/buried via. the manufacture capacity you listed above is a very common standard for a cheap fab in china. i do not know the quality they offer, but the price about the same compare to other Chinese fab.
my recommendation to lower the price is to increase the trace width, space to 4/4 mil or higher. and increase the diameter to 0.3mm or higher. try to reduce the size of the board. and do ask them for the laminate material. i suppose they use the 150-160 Tg FR-4 material for the price of 140.
the number of holes you want to drill usually does not matter much for small volume. last but not least, submit your design to multiply chinese fab. then you will have better choice on price.

[stevenhoneyman]

I'm (still) looking to move from QFN to BGA to be able to fit more stuff in to the same size board.

I would not call it high density PCBs. Your design do not contain via smaller than 1.5mm. and there is no blind/buried via. the manufacture capacity you listed above is a very common standard for a cheap fab in china.

Just in case there's some confusion - I agree, they're nowhere near high density... but they are definitely higher density than standard hobbyist specs (elecrow/itead/seeed/etc)

Good timing on your reply by the way, because the other day I received my first little test boards, which I went for the "cheat the specs" option and was sure to let them know that I was willing to accept any amount of failures caused by this. Interestingly, out of 10 boards, all of them were OK around the BGA part, but 4 of them are unusable due to drill alignment in the in-spec areas!

Here's one of the good ones (0.8 pitch, 12mil via drill, 4mil trace in the narrowest parts). The via on the right side, near the top is in-spec. any between BGA pads have a reduced annular ring.

[mikeselectricstuff]

Take a look at Wurth - they offer a lot of options, and cost adders for traces down to 0.1mm aren't that much. From memory smallest via pad after drill and annular ring ends up about 0.5mm, They also do HDI microvias but that gets really expensive
 http://www.wedirekt.co.uk/en/

[AndrewDojo]

I did a quick HDI "test case" study a couple of years back.

I took a fairly dense 2-layer board I had and reworked it as a 6 layer board using HDI methods to see how small I could get it.

My usual PCB fab company then quoted on the two designs.

Because of the significant reduction in board size for the HDI version, it wasn't anywhere near as expensive as I had feared.

The per cm^2 rate for the HDI board is much higher, but the number of cm^2's is reduced.

(I no longer have the hard numbers to quantify my findings)

[pcbfox]

maybe you can try  younghe-tech.com,  this may support you to make cost down ,

[technotronix]

I agree. The cost is to much, Go with two layer pcb instead 4 layer.

[tyrel]

the new seeedstudio fusion service can make PCB meeting all your requirements (4 layers, 4/4mils, 0.2mm vias) for as low as 100$.

[richardlawson1489]

Buy it online from the trusted PCB manufacturer.