Propeller 2 Package Information ( PCB Footprint )
Tubular
Posts: 4,621
Now that the design has been sent to the fab, is it possible to get a recommended PCB footprint, so we can make some PCBs to suit ?
thanks
Lachlan
thanks
Lachlan
Comments
We don't have an exact package yet, though I don't know if there's anything needed beyond "14mm-square-body TQFP-128".
Here are some drawings by Practical Components of this type of package
http://www.practicalcomponents.com/drawings/pdf/TQFP/A-TQFP128-14x14-1dwg.pdf
http://www.practicalcomponents.com/drawings/pdf/TQFP/A-TQFP128-14x14-2dwg.pdf
http://www.practicalcomponents.com/drawings/pdf/TQFP/A-TQFP128-14x14-3dwg.pdf
Have you checked if the P2 die will also bond in a MQFP80, 14x20mm, that has a lead pitch of 0.8mm, and may give a softer transition point ?
Jmg, I think that's a very good idea if it could be done. I wonder if it will fit.
Wilt, Jmg is referring to the way the existing Prop QFP package has a 0.8mm pitch, and many of us are used to hand or reflow soldering those. If the Prop2 could also have the same pin pitch (in that particular rectangular case), it eases the adoption process.
It may seem odd, but NOT having the leads stick out, may be better. Schmwartboards rely on the solder to flow under the package edge and connect with a natural viscosity of the liquid solder.
Exposed leads at 0.4mm may just be a rather huge shipping and handling headache, as well as a construction challenge. In other words, consider a different approach to smaller pins. Retrain your soldering technique rather than try to hold back the future.
http://www.youtube.com/watch?v=wUyetZ5RtPs
I really recommend .5mm as the tightest pitch. I would recommend using the QFN package for the .4mm pitch, maybe even BGA, and use .5mm for QFP.
That's my 2 cents, having reworked .4mm, .5mm, .65mm, and .8mm.
Romney, is that you? Your reality distortion field is turned on again!
EDIT: Now it's Crazy Busey! What's next, Nutz Nolte?
a digitally controlled static controlled soldering iron with a .015 pointed tip is mandatory.
It is also a good idea not to drink any coffee before soldering one of these chips down.
Russ
Out of maybe 20 or so boards I've made so far, I think only one didn't require rework on this big chip...
The worst part is that it's very difficult to see when pins are shorted together... I have to use a 10X loop to inspect all the pins...
That is the absolute minimum I'd recommend.
FWIW, there was an article on HAD about an STM32F4, which is comparable in pin count. Funny thing is, it's 168Mhz and rated at 210 DMIPS (a contrived C based benchmark). The P2 will be the same package and 1280 MIPS
One tactic that Parallax could take is to put the P2 die into a smaller pin count package, say, QFP-64 or PLCC-84, with reduced I/O, but easier for Hobbyists to handle.
There are several pitches inside those drawing files, I think its the TQFP-128 with 0.4mm (else I have a board to revise!)
Jmg suggested (reply #3 above) the 14x20mm MQFP80 with a 0.8mm pitch, same as the current prop qfp, which makes some sense too. Prop2 certainly has plenty of I/O, many applications won't need it all.
1.17mW per MHz per COG. That means with all 8 COGs running, 9.375mW per MHz.
It just so happens that the numbers are the same for MIPs, so it's 1.17mW per MIP or 651uA per MIP.
5.2mA per MHz with all 8 COGs running, 651uA per MHz per COG.
If using RCSLOW, and it's 20Khz like the Prop 1, that's 13uA per COG, 104uA for all COGs.
If using RCFAST, and it's 12Mhz like the Prop 1, that's 7.8125mA per COG, 62.5mA for all COGs.
Of course this is all speculative until they actually get silicon and can test it in the real world.
It's not about soldering skills. It's about PCB trace widths and clearances.
A 0.4mm pitch device requires a trace and space design rule that is less than 6mil.
This means I can't use cheap PCB services that need >= 7mil rules.
With 0.5mm pitch there are no such problems.
While I do not intend to make "developer" boards, I do have ideas for products, and 0.4mm spacing puts the current P2 plan off my radar.
I suspect that the 0.4mm package is less expensive.
Jazzed,
The 0.4mm means you need 8 mil services, (0.2mm pad and 0.2mm spacing is ~8 mil each). So just about anyone offers this level.
The board I just laid out uses 7 mil, which is also very widely available. There are just a couple of spots that need 6 mil, due to the Prop1 being included inside the Prop2 footprint temporarily (for testing; generally won't be required!), and they generally allow this
But the point is you can do it with 8 mil track & space if you want.
regards
Lachlan
According to the body tests I did this morning, I get DRC errors between QFP pads with 0.4mm pin spacing. There are different parameters for pins and track/space, but I get consistency warnings on having different rules.
The PCB fab houses seem to happily go a little bit below their minimum with no problems. I once had them phone up and complain at the 3 mil spacing level, which turned out to be an error in the ground pour rather than anything deliberate.
Anyway my point is there are plenty of fabrication options, 8 mil (ok 7.8 mil) is easy to find, and you certainly don't need < 6 mil as you suggested. ExpressPCB's 3 for $51 service goes down to 6 mil.
Just don't want people thinking it's impossible to do, thats all...
cheers
Lachlan
Steve,
OSH Park/Dorkbot PDX offers high quality boards for $5/inch in qty 3 prototype orders. Their minimum is 6 mil, and the quality is the absolute best you will get IMHO. I've used DipTrace and manually entered the specs for their boards, and it worked out great for stuff I've made.
Yes, PCBs via virtually any PCB FAB should be simple with (nominal) 8 mil rules.
I wonder if a special footprint is worth doing, ie with moved-fingers, tuned for manual assembly ?
Such a footprint would have PADS extending well past the package-ends, and stopping early under the fingers, so that bridges close to the package are less likely, and the longer PAD finger gives a solder-thieving effect during cleanup ?
PCB ends up a little larger than a mass-production design, but only slightly.
The smallest package would be BGA, and that is not industrial,or moderate-volume, friendly. Fine for cellphones - but not the Prop 2 target market..
So Gull-Wing wins, and a 0.4mm package is a good first choice there. (but it is not the smallest package possible).
Vendors in Asia are providing new parts in a choice of pitch, so there is obvious customer demand for the better yields that a larger pitch device brings. Not everyone is rushing to 'finest possible'.
Far from being retro, it is all about production yields, and sometimes on thickest-copper (high power) designs, a fine-pitch part can be a royal pain.
Dood, your trolling pseudo persona that you've registered is incredibly lame. I have no faith that Wilt Vine is your actual name, and none of your posts have been even the slightest bit helpful.
In short, please go troll some other board, or return to your other Parallax forum account which will strip you of your anonymity and keep you in line.
found that you can cut the leads with a sharp exacto knife then remove the chip. Then you can flood the remaining stubs
and lands with solder and carefully clean off the board with solder wick. The bottom line is to save the board, not the chip.
When I have new prototype boards made, I ask for a thick solder coating, then I flood the lands with flux and solder down
two pins to line up the chip. Then all you have to do is heat each land and the solder will flow to the chips lead.
Our board house has a minimum of 7 mil traces and spacing and a minimum hole size of 15 mil's to qualify for the
minimum standard cost. Be sure to make the power traces wider than usual for the P2, this will keep the voltage drop
to a minimum.