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[on:]

OSH's DRU minimums are 6 mil trace width / 6 mil spacing / 13 mil drill size / 7 mil annular ring.  In routing a 100 pin BGA part I have found that to meet these rules on a 2 layer board I have to make my pads 12 mils.  The default for this part is 16 mils.  So this gives me pause and I ran it by the guy who supports DipTrace over at their forum and he thinks it is not a good idea either.  The fact is, with these minimums, there doesn't seem to be any way to route the innermost pins on a 2 layer board without getting the pads down to 12 mils.  

Are there PCB manufacturers that have smaller DRUs than the ones I stated above that OSH Park uses?  This was the fanout I was able to get with OSH's minimums plus making the pads 12 mils.  It is the best I can do and the autorouter does worse.

[Reply #1 on:]

Itead goes smaller. I normally use 12mil drills with them.

[Reply #2 on:]

PCB capabilities for IteadStudio
(need conversions from mm to mil to mm:
10 mil = 0.254mm
.15mm = 5.9mil, call it 6 mil)

Layers
 1 - 4
 
Material
 FR-4

Board Dimension (max)
 500mm X1100mm
 
Board Dimension (min)
 10mm X10mm
 
Outline Dimension Accuracy
 ± 0.2mm >> 7.9mil
 
Board Thickness
 0.40mm--2.0mm >> 15.7mil to 78.7mil
 
Board Thickness Tolerance
 ± 10%
 
Dielectric Separation thickness
 0.075mm--5.00mm >> 3 mil to 197 mil
 
Conductor Width (min)
 0.15mm( Recommend>8mil ) >> 6mil
 
Conductor Space (min)
 0.15mm( Recommend>8mil) >> 6 mil
 
Outer Conductor thickness
 35um
 
Inner Conductor thickness
 17um--100um
 
Copper to Edge
 0.25mm,0.5mm >>10 mil, 20 mil  (why 2 numbers?)
 
Plated Component,Plated via Diameter(Mechanical)
 0.3mm--6.30mm >>12mil to 248 mil
 
Plated Hole Diameter Tolerance(Mechanical)
 0.08mm >> 3 mil
 
Unplated Hole Diameter Tolerance
 0.05mm >> 2 mil
 
Hole Space(min)
 0.25mm >> 10 mil
 
Hole to Edge
 0.4mm  >> 16 mil
 
Annular Ring(min)
 0.15mm >> 6 mil
 
Aspect Ratio
 8:01
 
Solder Resist Type
 Photosensitive ink
 
Solder Resist Color
 Black ,Green, White, Blue ,Yellow
 
Solder Resist Clearance
 0.1mm >>  4 mil
 
Solder Resist Coverage
 0.1mm >> 4 mil
 
Plug Hole Diameter
 0.25mm--0.60mm >>10 mil to 24 mil
 
Selective Finish
 HASL, ENIG
 

[Reply #3 on:]

I can confirm iTead's minimums as well.  I have done several 6mil traces and 10mil drills boards through them.

[Reply #4 on:]

I can confirm iTead's minimums as well.  I have done several 6mil traces and 10mil drills boards through them.

I'm not seeing how 6 mil traces beat 6 mil traces but 10 mil drills certainly beat 13 mil drills.

My only concern is seeing this:

http://hackaday.com/2012/09/11/bed-of-nails-and-accuracy-in-pcb-manufacturing/

Do you think this was an outlier?

[Reply #5 on:]

I see 64 pads around the perimeter. Where do the other 36 go? Pads on the bottom layer?
Looks like their might be a hint of another layer, kinda dark on my moniter, like dark brown on black.

[Reply #6 on:]

Any comments about pad size?   In DipTrace the default pad size for the Atmel 2560 CBGA is 16 mils.  Is 12 mils a show stopper?  How is that determined, manufacturer specified or CAD vendor specified or somethign else?

[Reply #7 on:]

Pad size for the balls should come from the spec sheet of the part you are using.
Pad size around the outside is your call for mating to traces for the rest of the board. Go as wide as you can while leaving 8-10mil clearance in between to meet DRU rules for trace clearance/seperation distance.

[Reply #8 on:]

From the datasheet for the ATmega640/1280/1281/2560/2561

In the details for the 100C1 CBGA:

Ball diameter: Min: 0.35mm (13.78 mil) Typ: 0.40mm (15.75 mil) Max: 0.45mm (17.72 mil)

It doesn't actually give a recommended landing pattern as such, unfortunately, like a lot of other data sheets do, so it's pretty much guesswork what the size should be.

16 mil is a good size as it's pretty much the "typical" ball size.  14 mil would be acceptable I guess at a pinch.

I wouldn't go below 14 mil - that's just asking for trouble.

[Reply #9 on:]

From the datasheet for the ATmega640/1280/1281/2560/2561

In the details for the 100C1 CBGA:

Ball diameter: Min: 0.35mm (13.78 mil) Typ: 0.40mm (15.75 mil) Max: 0.45mm (17.72 mil)

It doesn't actually give a recommended landing pattern as such, unfortunately, like a lot of other data sheets do, so it's pretty much guesswork what the size should be.

16 mil is a good size as it's pretty much the "typical" ball size.  14 mil would be acceptable I guess at a pinch.

I wouldn't go below 14 mil - that's just asking for trouble.

16 mil is exactly what DipTrace provides on that pattern so they agree with you.  I guess I will try again with 14 mil pads and see what I can get it to do.