Author Topic: PIC32MM, a Cortex-M0/M0+ contender?  (Read 17170 times)

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Offline Sal Ammoniac

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #75 on: June 29, 2016, 11:08:54 pm »
Unlike other technologies, fabbing your own boards for BGA is nigh on impossible not least because you really do need solder mask: without solder mask it's not pretty!

But is that really necessary? Getting a PCB fabbed professionally is dirt cheap these days, especially if you're willing to wait a few weeks, that I just don't see the need to fab them myself any more.
 

Offline Howardlong

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #76 on: June 30, 2016, 05:54:09 am »
Unlike other technologies, fabbing your own boards for BGA is nigh on impossible not least because you really do need solder mask: without solder mask it's not pretty!

But is that really necessary? Getting a PCB fabbed professionally is dirt cheap these days, especially if you're willing to wait a few weeks, that I just don't see the need to fab them myself any more.

It's still not dirt cheap to prototype small volume runs if you want BGA: realistically doing a BGA fanout will need 4mil track and gap, not typically found in pool services.

But having to wait a few weeks is a deal killer for me, by then I'll have moved on.

If you're very patient (more so than me!) and don't mind paying a premium for the tolerances, then sure. Which in some respects brings us back the earlier discussion about how quick it is the prototype in surface mount compared to DIP.
 

Offline TheDirty

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #77 on: June 30, 2016, 06:28:31 pm »
Not a professional, just a hobbyist, but I still make my own boards.  Shipping from China to Canada has gotten to be at a minimum 4 weeks so Chinese proto boards are taking a ridiculous amount of time.  As far as time, I find free wiring stuff like the picture above takes too much time and is prone to error.  Making up a single sided board, etching, and drilling takes 20 minutes (timed myself).  No BGA of course, but everything else I've tried, DFN, QFN...

No comment on the speed of dip prototyping, but I haven't used a DIP package in a few years.  EDIT:  Not true, ordered a couple PIC12f1840's in DIP8 package.  I can't think of anything else.
Mark Higgins
 

Offline Howardlong

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #78 on: June 30, 2016, 08:15:48 pm »
Not a professional, just a hobbyist, but I still make my own boards.  Shipping from China to Canada has gotten to be at a minimum 4 weeks so Chinese proto boards are taking a ridiculous amount of time.  As far as time, I find free wiring stuff like the picture above takes too much time and is prone to error.  Making up a single sided board, etching, and drilling takes 20 minutes (timed myself).  No BGA of course, but everything else I've tried, DFN, QFN...

No comment on the speed of dip prototyping, but I haven't used a DIP package in a few years.  EDIT:  Not true, ordered a couple PIC12f1840's in DIP8 package.  I can't think of anything else.

My own PCB fab process takes 30 minutes beginning to end (assuming I have the board already designed) including getting the chemicals out to putting them away again. Unfortunately living in an apartment I don't have a dedicated space for this, it happens in the kitchen  :-[  I almost uniquely prefer surface mount for PCBs because only vias need drilling.

The typical design process I take for prototyping any non-trivial design is incremental. Rather than put everything together in one go, I unit test each section. This works reasonably well with bread- and proto boards on the low to medium speed digital side, but for RF I fab each section on a PCB for unit test and glue those together like Lego.

Once I have everything unit tested it's time to put them all together onto a single board design, and go to the board house. If I'm lucky, only one or two spins later I have a production board.

 

Offline Sal Ammoniac

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #79 on: June 30, 2016, 11:49:39 pm »
If you're very patient (more so than me!) and don't mind paying a premium for the tolerances, then sure. Which in some respects brings us back the earlier discussion about how quick it is the prototype in surface mount compared to DIP.

I always have several projects in the pipeline, so when I send a board out to be fabbed I just switch to another project and write firmware, or do board layout, or whatever, until the PCB arrives and then I switch back to that project.
 

Offline nctnico

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #80 on: July 01, 2016, 12:01:25 am »
I do the pipelining too but looking at Howard's boards having those made will take too long. I'd probably etch such boards myself to have a prototype to work with the same day.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline boz

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #81 on: July 02, 2016, 02:02:23 am »
Nice chip. Good to see Microchip making the investment for us poor deluded retards who quite like the pic32 (DIP and SMT Versions).  I also like Pepsi over Coke and prefer Fords over GM for those that like a real argument.
Fearless diver and computer genius
 

Offline asgard20032

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #82 on: July 02, 2016, 05:58:53 am »
The problem of surface mount vs dip, is not soldering, but getting those breakout board. They also can get quite expansive and even cost the same as the chip. MCU : 3$, breakout : 4$... Its not rare to see such price.
 

Online andersm

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #83 on: July 02, 2016, 06:37:54 am »
They also can get quite expansive and even cost the same as the chip.
For simple prototyping supplies like that, I have no problem ordering from eBay where you can get fifty of the smaller boards for three bucks, delivered. They're probably not going to be of as high quality as your five-dollar DigiKey board, but they're good enough.

Offline Howardlong

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #84 on: July 02, 2016, 06:57:50 am »
They also can get quite expansive and even cost the same as the chip.
For simple prototyping supplies like that, I have no problem ordering from eBay where you can get fifty of the smaller boards for three bucks, delivered. They're probably not going to be of as high quality as your five-dollar DigiKey board, but they're good enough.

I'd whole heartedly agree with that, investing in a stash of various boards is worthwhile, the biggest problem being that there are so many varieties.

I also keep a stock of Schmartboards many of which have the benefit of a ground plane. While it's still no substitute for a properly designed PCB you can do at least some mixed signal on them. They are expensive though. I have in the past made my own breakout boards, and still do if necessary, but having a stock is one less step to your next prototype.

These are the contents of my breakout drawer...

 

Offline westfw

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #85 on: July 02, 2016, 06:59:30 am »
Speaking in isolation of political factors, I think that it is very good that there is at least one microcontroller vendor that is implementing something other than the most recent ARM core, and the MIPS core is a natural alternative.  It ought to be technically viable as well, but it's a little surprising how being the only implementer works against microchip...
 

Offline Howardlong

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #86 on: July 02, 2016, 07:24:29 am »
While I've been using PICs or their forerunners for decades, I do also work on hardware and firmware for ARM from M0 to M4F (TI & NXP) quite extensively, and quite recently I was working on an Atmel AT32UC3C for the first time.

What concerns me is that there's a school of thought that seems to suggest that once you have picked an ARM then you can use that experience across every ARM. Practically speaking, there's so little common ground across the mutitude of ARM platforms, including both the chips implementations themselves and the development platforms, there isn't much benefit to stipulating ARM as a fundamental requirement.

More important is going to be if a device has the right amount of memory, performance, peripherals and price, plus of you already have a dev team with skills in a given vendor's devices, there's a significant cost in time and money to switch.

Having awareness of what's out there is certainly a benefit, but I think that to simplify it down to ARM vs everything else doesn't bear much scrutiny.
 

Offline bktemp

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #87 on: July 02, 2016, 07:27:41 am »
I'd whole heartedly agree with that, investing in a stash of various boards is worthwhile, the biggest problem being that there are so many varieties.
It can be really annoying. Almost every manufacturer has its own package variations. I recently had to build a prototype using a small 8 pin IC. I had 0.5mm breakout boards but the package width was completely different, so I had to cut the breakout board to adjust the distance of both pin rows. It was some extra wide DFN package I had never seen before.
0.4mm, 0.5mm, 0.635mm, 0.65mm. So many variants, some with pins others DFN/QFN. For QFP/SOP many different pin counts can share the same board, but that does not work for QFN/DFN because of the thermal pad shorting any exposed pads. So for QFN/DFN every package needs its own breakout board.
 

Offline mikeselectricstuff

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #88 on: July 02, 2016, 09:10:15 am »
. For QFP/SOP many different pin counts can share the same board, but that does not work for QFN/DFN because of the thermal pad shorting any exposed pads. So for QFN/DFN every package needs its own breakout board.
As long as you don't need the thermal pad, which is often the case, you can usually get away with covering it with kapton tape
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Offline bktemp

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #89 on: July 02, 2016, 10:15:35 am »
. For QFP/SOP many different pin counts can share the same board, but that does not work for QFN/DFN because of the thermal pad shorting any exposed pads. So for QFN/DFN every package needs its own breakout board.
As long as you don't need the thermal pad, which is often the case, you can usually get away with covering it with kapton tape
That's the quick&dirty solution I often use if I don't have a perfectly matching breakout board.
Some parts require the pad for electrical reasons. One example is Altera Cyclone IV in TQFP. It has a pad that needs to be connected to GND, otherwise it does not work at all. My TQFP144 breakout board needed some modifications to make it work.
I also had some QFN/DFN ics that didn't require any connection to the pad, but if left unconnected the chip behaved different. That's why I always try to connect the pad to GND (or the most negative voltage for some ics), even when using breakout boards. If possible, I avoid QFN/DFN because of the centre pad for prototypes.
 

Offline Howardlong

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #90 on: July 02, 2016, 12:51:43 pm »
The ground pad is one of the problems of QFN prototyping boards. Some chips have it connected to ground, others it's floating, but still needs connecting. QFN boards with proper ground lands and vias aren't a problem, but some don't have both of these facets. Some have the plated through via but no land. It's about a 1mm via, so bigger than normal, but you can't get an iron down it. I have no idea what the point of that is, it's very difficult to make the ground pad connection as the solder is wicked down the via, and the device slightly floats above the pad. Reflowing is equally hot and miss.

One trick I do if the pad is connected internally to ground is to use it as a reference, and switch the meter to diode test. You can then quickly test every land has connection. If the pad's not connected to anything on the chip you're out of luck.
 

Offline nctnico

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #91 on: July 02, 2016, 02:18:18 pm »
With QFN packages I put a couple of vias in the the pad for the ground pad. When soldering I fix the outer pins first and then I let the solder flow into one via of the ground pad and wait until the solder comes up into the other vias. Sometimes I use hot air in case of a multilayer board but this trick works very well either way (also for TSSOP and other packages with a ground pad).
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline dannyf

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #92 on: July 02, 2016, 07:47:02 pm »
The logic for a capacitor tester seems to be simple, measure the voltage and the current, and update the energy discharged. done.

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Offline benSTmax

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #93 on: July 02, 2016, 09:28:53 pm »
It is funny to read all these intricate methods for just soldering a package like (QFP, QFN, DFN, ...) when in the end the whole 2nd part of this discussion on the packages started between people defending the DIP and other blaming it. Yes, DIP is old but it still gets the job done for quite a few of us.

The neat thing about Microchip is they still offer this old packages which is easy to prototype with.  Once, I was in contact with a Microchip support guy and he told me the DIP variants are being specifically offered, so students, hobbyists and others can play with their chips. They weren't selling high volumes of this package, however the DIP helped in the long run to sell more of the QFP, QFN, ... (much smaller than DIP) packages.
I guess he was right. I followed the same path with one of their chips. I put it on the prototype board and once the module I built around it worked as expected, I integrated with the rest of the modules. Afterwards, I switched to a small PCB and a QFN variant of the same chip. Indeed, the DIP package I played with helped the sale of its QFN variant.
« Last Edit: July 02, 2016, 09:30:26 pm by benSTmax »
 

Offline Howardlong

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #94 on: July 02, 2016, 09:41:24 pm »
Anecdotally I'd agree with you in my experience, I prototyped two designs recently with low pin count PICs in DIP. In system testing and production I switched to QFN, we're now at 20ku as I write. While it's not 7 figures, it's not chicken feed either.

Back to QFN prototyping, the boards I was referring to with the rubbish ground lands are Schmartboards. I generally rave over these because they have a solid ground plane, just a shame they make if so hard to solder the ground pad.

 

Online andersm

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Re: PIC32MM, a Cortex-M0/M0+ contender?
« Reply #95 on: July 02, 2016, 11:26:25 pm »
With DIP you're seriously limiting your choices of parts, and not just when it comes to MCUs. And while they may be appreciated by beginners, I think a modern hobbyist or student is more likely to use a header board or a complete module like an Arduino.


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