TQFP handling while developing

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Hi @ll

Microchip offers his new controllers (i.e. dsPIC) with > 40 leads only
in the TQFP but not PLCC package. Sockets for TQFP are not reliable.
Thus they are no solution.  

What does that mean? The original PCB cannot longer be used for
developement, because sockets are not possible. You have to design a
special PCB for that.

The only way I found, is to solder the device under test on a special
adapter PCB, which fits in a special socket on special designed
application PCB.

Are there other possibilities? How do you handle this?

--
Paul dankt den Helfern,
wünscht jedem viel Spaß im Usenet
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Re: TQFP handling while developing
It should be possible to solder the TQFP package into the application board
and develop on that board. Provided you don't blow the DSPIC up, you should
not need to remove it for debugging or programming - it's FLASH

-Andrew

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Re: TQFP handling while developing

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What is the problem in creating an application specific board with
everything on that is required for the project ?
I do at least a board per project.
Debugging is done on the board with an in circuit programmer.
Those flash devices do at least 1000 cycles, usually sufficient
to solve the problem.


Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

Re: TQFP handling while developing

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The problem is, that you do not know before what hardware you need for
a project, even in analog-applications. Software and hardware are
developed together. You have not only to change the software, but also
the hardware. And sometimes you need more than one controller. You
cannot use a new board for maybe every 20 versions, because you cannot
produce TQFD boards yourself. You have to give it away. And only one
PCB is very expensiv and needs much time. If you could produce the PCB
yourself, you make some changes in the layout and get a new one in
half an hour.

Further controllers can be damaged, when you have a wild mess of
soldered components. Especiallly audio-design and picoampere/microvolt
measurings and applications with switched high voltage/currents are
very messed, because her special demands of astral routing.

Because all that I have to solder the TQFP-processor on a special
ilittle board, which can be inserted in the application developement
board.

Further there is another problem: If you have finished developing with
the adapted TQFP Controllers, you have to route the PCB new for the
not adapted series version. And then things change. The audio or the
measuring is wrong now, because disturbed by the controller. Or the
application disturbes the processor now and it crashes.

And what is about emulation, when the processor is soldered into the
board?

With socketable controllers like PLCC things were much easier. You
could socket it and change it, when damaged. You could produce the
developement versions of PCB yourself. Emulation is no problem: Plug
the emulator into the socket of the controller. And the last
developement version could without problems be the series version. And
if you get problems to leave out the socket in the series version, you
let him be,

Even for DS you need a controller, which has the same format in the
development and the series version. And for this purpose PLCC was a
good solution. It is the skimpiest format, that is reliable
socketable. But of all things the DS!!-PIC is not available in this
package. Maybe this shows, that mirochip is new in the
(digital-)analog segment and is not familiar with its problems.

--
Paul dankt den Helfern,
wünscht jedem viel Spaß im Usenet
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Re: TQFP handling while developing
Thank you, Paul for your long answer.

First I want to say, that my English is not very good. I do not know,
whether I understood everything correctly. And do not know, whether I
say everything that way, I want it to say. Sorry for this.


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This is a problem. I am the only designer in our company. The
possibilities are a bit poor. :-(  I have to solve every problem
without companion and without assistance.

What is a naff project contol? Or better: What makes a project control
the opposite of naff?

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Could you explain that with other words ... my limited English.
Sometimes I think, a good equipment makes your thoughts poor. I do not
really know, which side is better to switch charitable mode on or off.
;-)  But the die of PLCC is too hard. Some effects maybe compensated,
but others not.

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You are speaking from the little PCBs with the controller on it?
Please, tell me more about "impedance controlled padding".

The analog section is devided from the digital by both grounds, which
goes closed to the controller as possible. The backside (two layers)
of the pcb is filled with ground - digital and analog devided to their
sections.

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Very good!!

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Isn't it capacity? Please, tell me more.
 
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I think I do it. Maybe there are some points, which I do not know.I
use two or more grounds. Every section is screened by its own ground.
Critical signals are double screened with its own signal, hardened by
an amp and then with its ground. Astral wiring as most as possible..
Very critical points (high impedance) are devided by gaps in the PCB
or sometimes wired in the air. In extreme situatuations they are
sealed from the humidity. I use screen-sheets. I always use
kelvin-design for critical measurements. I decouple wires with high
and low current. The thermo effect of a soldering joint is annihilated
by an inverse one, if disturbing. I take care of the route of every
lead. I decouple switched high-voltage leads by resistances near to
the switches, to avoid broadcast. This all for PCB route and real wire
route. I hope I did not forget anything. Anything more to do?

But there is the mechanical process equipment, which is not always
asked me. And sometimes the design of the electronic is made by
optical aspects. They do not want the electronic to "get cluttered" to
different places of the equipment, which would be useful for good
decoupling. And sometimes the mechanical eqipment lets you not do,
what would be good to avoid crosstalk and pickup. Although this, you
have to provide a working design. And that could make problems when
changing a working prototype layout because TQFP. But it helps, what
you said above.
 
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Still unanswered
 
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They said, that I could program the controllers in-curcuit. I know
that. This helps only for the software, but not for the hardware.

Maybe, I should calm down  But that does not change this fact: The die
of PLCC makes problems for analog-developement not easier. And I am
quite safe, that this bothers not only me.

--
Paul dankt den Helfern,
wünscht jedem viel Spaß im Usenet
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Re: TQFP handling while developing

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Careful design ...

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I never used an emulator. They were to expensive to start with and
meanwhile I have debugging techniques that are sufficient.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

Re: TQFP handling while developing
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Vendors (initially) offer TQFP/SMD only, because that is where the
volume business is.

It can, and does, change : examples
- Cygnal offer selected DIP packages of their MLF production devices
- Philips original LPC932 family did not include PLCC package, now, they
      do.
- IIRC, Atmels first data on the AT89C51ED2 also excluded PDIP, but now
this is included.

So, mention it to Microchip.

If it is a 'show stopper', choose another uC...

-jg


Re: TQFP handling while developing

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To the rehabilitation of Microchip I must say, that they offer
DIP-dsPICs. But this is only possible until 40 leads. The PLCC would
be the better solution, because it is smaller and all the same
reliable contactable. And it has got more leads.

--
Paul dankt den Helfern,
wünscht jedem viel Spaß im Usenet
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