On 8/23/2016 7:14 PM, Tim Williams wrote:
> "rickman" <gnuarm@gmail.com> wrote in message
> news:npi5oj$m5j$1@dont-email.me...
>> For the most part, QFNs are just QFP packages with the leads cut off.
>> I suppose there are some smaller pin count packages which have not
>> corresponding QFPs and they can be uniquely small.  But a 100 pin QFN
>> has the same body size as a 100 pin QFP.  I have seen QFNs with
>> multiple rows of pads, but technically, I believe they become LGAs, no?
>
> Right, and the lead lengths plus pad toe length, plus tolerances, takes
> up a good 4mm or so around it.
>
> You can use that for routing instead.

QFNs have pads and toe lengths and tolerances as well.  I believe the 
difference ends up being 2 mm which is the extent of the leads on the 
QFP.  So for smaller devices this can be appreciable but much less an 
issue with larger packages like a 48 or 64 pin device.


> I kind of suspect QFPs are easier to route anyway, as there's no pad in
> the middle (usually) that ties up all layers, grounding it.  You have
> very little room to do that under a QFN, so you end up using the pin+pad
> area for routing instead.

Or worse.  My typical designs have very limited space and the loss of 
room for vias is a problem with QFNs.  I like them, but mostly for 
smaller parts like 20 pin parts.  I like BGAs a lot less.  Mostly they 
require finer pitch lines and spaces as well as micro vias driving up 
the cost of the PCB.


>> Not sure what you mean, "every which way".  Are you talking about pads
>> on all surfaces like a porcupine?  The QFN parts I have seen were
>> still all planer.
>
> As Lasse noted, I mean the pinout of GPIO ports and buses.

I've never found a problem with that.  Buses are a bit dated unless you 
are designing with external memory, not my typical design.  Otherwise I 
find I can assign the I/O to suit my board routing.  Heck, when I design 
with FPGAs, I do a schematic and then redo the pinout to optimize my 
board routing.  Some designs just would not fit on the board if I 
didn't, at least not without more layers.

> Even SCK, MISO and MOSI end up jumbled!  How the hell?

How can you care about routing three signals?  What would you expect for 
a pinout?


> One plus about ATmegas is their pinouts are always nice.

I use FPGAs a lot more than micros.  FPGAs will do anything a typical 
MCU will do, but not the converse.  MCUs are useful if you need a lot of 
complex software to do the job.  It would be hard to implement an IP 
stack in VHDL... unless you implement a CPU which I have done. 
Sometimes it's just easier to include it in the FPGA than to add another 
device and programming port and crystal and...

-- 

Rick C

On Tue, 23 Aug 2016 14:47:49 -0400, rickman <gnuarm@gmail.com> wrote:

>On 8/23/2016 8:46 AM, Tim Williams wrote:
>> "rickman" <gnuarm@gmail.com> wrote in message
>> news:npg0f3$7s1$6@dont-email.me...
>>>> Do they make QFN adapters? There's a post-it on my door that says NO
>>>> QFNS. Everybody hates them.
>>>
>>> Yeah, those who aren't very good at manufacturing don't like them.
>>> That's why I'd never consider building my own assembly line.  Contract
>>> manufacturers don't seem to have any problem with them... or the big
>>> builders who have to save every penny they can, like in cell phones,
>>> etc. QFNs are very common and very useful.
>>
>> I love QFNs!  Good thermal performance, smaller than QFP and more
>> reliable, and impossible to short between pins (which was interesting as
>> I had some rework recently where I had to add a short between pins..).
>
>For the most part, QFNs are just QFP packages with the leads cut off.

Bullshit.  They're completely different packages.  

"rickman" <gnuarm@gmail.com> wrote in message 
news:npi5oj$m5j$1@dont-email.me...
> For the most part, QFNs are just QFP packages with the leads cut off.  I 
> suppose there are some smaller pin count packages which have not 
> corresponding QFPs and they can be uniquely small.  But a 100 pin QFN has 
> the same body size as a 100 pin QFP.  I have seen QFNs with multiple rows 
> of pads, but technically, I believe they become LGAs, no?

Right, and the lead lengths plus pad toe length, plus tolerances, takes up a 
good 4mm or so around it.

You can use that for routing instead.

I kind of suspect QFPs are easier to route anyway, as there's no pad in the 
middle (usually) that ties up all layers, grounding it.  You have very 
little room to do that under a QFN, so you end up using the pin+pad area for 
routing instead.


> Not sure what you mean, "every which way".  Are you talking about pads on 
> all surfaces like a porcupine?  The QFN parts I have seen were still all 
> planer.

As Lasse noted, I mean the pinout of GPIO ports and buses.

Even SCK, MISO and MOSI end up jumbled!  How the hell?

One plus about ATmegas is their pinouts are always nice.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com 

On 8/23/2016 4:19 PM, Lasse Langwadt Christensen wrote:
> Den tirsdag den 23. august 2016 kl. 21.41.04 UTC+2 skrev rickman:
>> On 8/23/2016 3:36 PM, Lasse Langwadt Christensen wrote:
>>> Den tirsdag den 23. august 2016 kl. 20.47.52 UTC+2 skrev rickman:
>>>> On 8/23/2016 8:46 AM, Tim Williams wrote:
>>>>> "rickman" <gnuarm@gmail.com> wrote in message
>>>>> news:npg0f3$7s1$6@dont-email.me...
>>>>>>> Do they make QFN adapters? There's a post-it on my door that says NO
>>>>>>> QFNS. Everybody hates them.
>>>>>>
>>>>>> Yeah, those who aren't very good at manufacturing don't like them.
>>>>>> That's why I'd never consider building my own assembly line.  Contract
>>>>>> manufacturers don't seem to have any problem with them... or the big
>>>>>> builders who have to save every penny they can, like in cell phones,
>>>>>> etc. QFNs are very common and very useful.
>>>>>
>>>>> I love QFNs!  Good thermal performance, smaller than QFP and more
>>>>> reliable, and impossible to short between pins (which was interesting as
>>>>> I had some rework recently where I had to add a short between pins..).
>>>>
>>>> For the most part, QFNs are just QFP packages with the leads cut off.  I
>>>> suppose there are some smaller pin count packages which have not
>>>> corresponding QFPs and they can be uniquely small.  But a 100 pin QFN
>>>> has the same body size as a 100 pin QFP.  I have seen QFNs with multiple
>>>> rows of pads, but technically, I believe they become LGAs, no?
>>>>
>>>>
>>>>> What I don't like is the MCUs that invariably have pins coming out every
>>>>> which way. MSP430s do it. STM32s do it.  The hell is up with that?  Why
>>>>> would 32 bits of bus end up jumled!?  It literally takes as much PCB
>>>>> space to rout such a QFN, as the QFP takes up!  (The QFP would still be
>>>>> worse, though routing underneath is easier at least, not needing to
>>>>> allow for a ground pad.)
>>>>
>>>> Not sure what you mean, "every which way".  Are you talking about pads
>>>> on all surfaces like a porcupine?  The QFN parts I have seen were still
>>>> all planer.
>>>>
>>>
>>> I suspect he means that pins that would naturally be grouped together, like
>>> a data bus are spread out in a seemly  random fashion, so to route a memory
>>> bus you need to get to all four sides of the chip and swap the order on the way
>>
>> Why would that be any different from any other package?  The order of
>> pins on the package is usually the same or close to the order of pins on
>> the die.
>
> not really any different, it's just that the idea of a small package is
> somewhat lost if the area you gain is just lost in routing and vias

Yes, to some extent.  But real estate can be reclaimed by using smaller 
PCB features and adding layers.  In some cases, size is more important 
that cost, so it's ok to transfer some cost to the PCB even if it ends 
up being more in total.

-- 

Rick C

Den tirsdag den 23. august 2016 kl. 21.41.04 UTC+2 skrev rickman:
> On 8/23/2016 3:36 PM, Lasse Langwadt Christensen wrote:
> > Den tirsdag den 23. august 2016 kl. 20.47.52 UTC+2 skrev rickman:
> >> On 8/23/2016 8:46 AM, Tim Williams wrote:
> >>> "rickman" <gnuarm@gmail.com> wrote in message
> >>> news:npg0f3$7s1$6@dont-email.me...
> >>>>> Do they make QFN adapters? There's a post-it on my door that says NO
> >>>>> QFNS. Everybody hates them.
> >>>>
> >>>> Yeah, those who aren't very good at manufacturing don't like them.
> >>>> That's why I'd never consider building my own assembly line.  Contract
> >>>> manufacturers don't seem to have any problem with them... or the big
> >>>> builders who have to save every penny they can, like in cell phones,
> >>>> etc. QFNs are very common and very useful.
> >>>
> >>> I love QFNs!  Good thermal performance, smaller than QFP and more
> >>> reliable, and impossible to short between pins (which was interesting as
> >>> I had some rework recently where I had to add a short between pins..).
> >>
> >> For the most part, QFNs are just QFP packages with the leads cut off.  I
> >> suppose there are some smaller pin count packages which have not
> >> corresponding QFPs and they can be uniquely small.  But a 100 pin QFN
> >> has the same body size as a 100 pin QFP.  I have seen QFNs with multiple
> >> rows of pads, but technically, I believe they become LGAs, no?
> >>
> >>
> >>> What I don't like is the MCUs that invariably have pins coming out every
> >>> which way. MSP430s do it. STM32s do it.  The hell is up with that?  Why
> >>> would 32 bits of bus end up jumled!?  It literally takes as much PCB
> >>> space to rout such a QFN, as the QFP takes up!  (The QFP would still be
> >>> worse, though routing underneath is easier at least, not needing to
> >>> allow for a ground pad.)
> >>
> >> Not sure what you mean, "every which way".  Are you talking about pads
> >> on all surfaces like a porcupine?  The QFN parts I have seen were still
> >> all planer.
> >>
> >
> > I suspect he means that pins that would naturally be grouped together, like
> > a data bus are spread out in a seemly  random fashion, so to route a memory
> > bus you need to get to all four sides of the chip and swap the order on the way
> 
> Why would that be any different from any other package?  The order of 
> pins on the package is usually the same or close to the order of pins on 
> the die.

not really any different, it's just that the idea of a small package is
somewhat lost if the area you gain is just lost in routing and vias

-Lasse

On 8/23/2016 3:36 PM, Lasse Langwadt Christensen wrote:
> Den tirsdag den 23. august 2016 kl. 20.47.52 UTC+2 skrev rickman:
>> On 8/23/2016 8:46 AM, Tim Williams wrote:
>>> "rickman" <gnuarm@gmail.com> wrote in message
>>> news:npg0f3$7s1$6@dont-email.me...
>>>>> Do they make QFN adapters? There's a post-it on my door that says NO
>>>>> QFNS. Everybody hates them.
>>>>
>>>> Yeah, those who aren't very good at manufacturing don't like them.
>>>> That's why I'd never consider building my own assembly line.  Contract
>>>> manufacturers don't seem to have any problem with them... or the big
>>>> builders who have to save every penny they can, like in cell phones,
>>>> etc. QFNs are very common and very useful.
>>>
>>> I love QFNs!  Good thermal performance, smaller than QFP and more
>>> reliable, and impossible to short between pins (which was interesting as
>>> I had some rework recently where I had to add a short between pins..).
>>
>> For the most part, QFNs are just QFP packages with the leads cut off.  I
>> suppose there are some smaller pin count packages which have not
>> corresponding QFPs and they can be uniquely small.  But a 100 pin QFN
>> has the same body size as a 100 pin QFP.  I have seen QFNs with multiple
>> rows of pads, but technically, I believe they become LGAs, no?
>>
>>
>>> What I don't like is the MCUs that invariably have pins coming out every
>>> which way. MSP430s do it. STM32s do it.  The hell is up with that?  Why
>>> would 32 bits of bus end up jumled!?  It literally takes as much PCB
>>> space to rout such a QFN, as the QFP takes up!  (The QFP would still be
>>> worse, though routing underneath is easier at least, not needing to
>>> allow for a ground pad.)
>>
>> Not sure what you mean, "every which way".  Are you talking about pads
>> on all surfaces like a porcupine?  The QFN parts I have seen were still
>> all planer.
>>
>
> I suspect he means that pins that would naturally be grouped together, like
> a data bus are spread out in a seemly  random fashion, so to route a memory
> bus you need to get to all four sides of the chip and swap the order on the way

Why would that be any different from any other package?  The order of 
pins on the package is usually the same or close to the order of pins on 
the die.

-- 

Rick C

Den tirsdag den 23. august 2016 kl. 20.47.52 UTC+2 skrev rickman:
> On 8/23/2016 8:46 AM, Tim Williams wrote:
> > "rickman" <gnuarm@gmail.com> wrote in message
> > news:npg0f3$7s1$6@dont-email.me...
> >>> Do they make QFN adapters? There's a post-it on my door that says NO
> >>> QFNS. Everybody hates them.
> >>
> >> Yeah, those who aren't very good at manufacturing don't like them.
> >> That's why I'd never consider building my own assembly line.  Contract
> >> manufacturers don't seem to have any problem with them... or the big
> >> builders who have to save every penny they can, like in cell phones,
> >> etc. QFNs are very common and very useful.
> >
> > I love QFNs!  Good thermal performance, smaller than QFP and more
> > reliable, and impossible to short between pins (which was interesting as
> > I had some rework recently where I had to add a short between pins..).
> 
> For the most part, QFNs are just QFP packages with the leads cut off.  I 
> suppose there are some smaller pin count packages which have not 
> corresponding QFPs and they can be uniquely small.  But a 100 pin QFN 
> has the same body size as a 100 pin QFP.  I have seen QFNs with multiple 
> rows of pads, but technically, I believe they become LGAs, no?
> 
> 
> > What I don't like is the MCUs that invariably have pins coming out every
> > which way. MSP430s do it. STM32s do it.  The hell is up with that?  Why
> > would 32 bits of bus end up jumled!?  It literally takes as much PCB
> > space to rout such a QFN, as the QFP takes up!  (The QFP would still be
> > worse, though routing underneath is easier at least, not needing to
> > allow for a ground pad.)
> 
> Not sure what you mean, "every which way".  Are you talking about pads 
> on all surfaces like a porcupine?  The QFN parts I have seen were still 
> all planer.
> 

I suspect he means that pins that would naturally be grouped together, like 
a data bus are spread out in a seemly  random fashion, so to route a memory 
bus you need to get to all four sides of the chip and swap the order on the way

-Lasse

On 8/23/2016 8:46 AM, Tim Williams wrote:
> "rickman" <gnuarm@gmail.com> wrote in message
> news:npg0f3$7s1$6@dont-email.me...
>>> Do they make QFN adapters? There's a post-it on my door that says NO
>>> QFNS. Everybody hates them.
>>
>> Yeah, those who aren't very good at manufacturing don't like them.
>> That's why I'd never consider building my own assembly line.  Contract
>> manufacturers don't seem to have any problem with them... or the big
>> builders who have to save every penny they can, like in cell phones,
>> etc. QFNs are very common and very useful.
>
> I love QFNs!  Good thermal performance, smaller than QFP and more
> reliable, and impossible to short between pins (which was interesting as
> I had some rework recently where I had to add a short between pins..).

For the most part, QFNs are just QFP packages with the leads cut off.  I 
suppose there are some smaller pin count packages which have not 
corresponding QFPs and they can be uniquely small.  But a 100 pin QFN 
has the same body size as a 100 pin QFP.  I have seen QFNs with multiple 
rows of pads, but technically, I believe they become LGAs, no?


> What I don't like is the MCUs that invariably have pins coming out every
> which way. MSP430s do it. STM32s do it.  The hell is up with that?  Why
> would 32 bits of bus end up jumled!?  It literally takes as much PCB
> space to rout such a QFN, as the QFP takes up!  (The QFP would still be
> worse, though routing underneath is easier at least, not needing to
> allow for a ground pad.)

Not sure what you mean, "every which way".  Are you talking about pads 
on all surfaces like a porcupine?  The QFN parts I have seen were still 
all planer.

-- 

Rick C

On Tuesday, 23 August 2016 13:46:48 UTC+1, Tim Williams  wrote:

> I love QFNs!  Good thermal performance, smaller than QFP and more reliable, 
> and impossible to short between pins (which was interesting as I had some 
> rework recently where I had to add a short between pins..).

Also, the RF emissions should be lower as there should be less
ground bounce.

John

"rickman" <gnuarm@gmail.com> wrote in message 
news:npg0f3$7s1$6@dont-email.me...
>> Do they make QFN adapters? There's a post-it on my door that says NO
>> QFNS. Everybody hates them.
>
> Yeah, those who aren't very good at manufacturing don't like them. That's 
> why I'd never consider building my own assembly line.  Contract 
> manufacturers don't seem to have any problem with them... or the big 
> builders who have to save every penny they can, like in cell phones, etc. 
> QFNs are very common and very useful.

I love QFNs!  Good thermal performance, smaller than QFP and more reliable, 
and impossible to short between pins (which was interesting as I had some 
rework recently where I had to add a short between pins..).

What I don't like is the MCUs that invariably have pins coming out every 
which way. MSP430s do it. STM32s do it.  The hell is up with that?  Why 
would 32 bits of bus end up jumled!?  It literally takes as much PCB space 
to rout such a QFN, as the QFP takes up!  (The QFP would still be worse, 
though routing underneath is easier at least, not needing to allow for a 
ground pad.)

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com