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'[EE] QFN packaging experiences anyone?'
2008\04\23@065741 by Stephen R Phillips

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Anyone have experience with designing with said packaging for devices?

Apart from the finer pitch and .. no leads (heh) what is the biggest issues that might come up with routing?  My biggest concern is routing area, it appears that these will use less routing area than QFP packaging with the same main package and shorter leads.

Can these be hand assembled? TI seems to think so, hence the question.

I thought there was an [ARM] discussion on the PIC list but I've either not received any messages or there isn't. (random thought)

Erstwhile I said PIC and this is EE related so it's mostly on topic right?

Stephen


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2008\04\23@071349 by peter green

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> Apart from the finer pitch and .. no leads (heh) what is the biggest issues that might come up with routing?  

Only routed them a couple of time but the ones I dealt with had a big
ground pad in the middle which basically meant the area under the chip
was unusable for routing.

Combine that with the fact that unless you are on a very fine process
your via spacing will end up considerablly wider than the pad spacing of
the chip and routing can get rather annoying/space consuming.

2008\04\23@072122 by Spehro Pefhany

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At 06:57 AM 4/23/2008, you wrote:
>Anyone have experience with designing with said packaging for devices?
>
>Apart from the finer pitch and .. no leads (heh) what is the biggest
>issues that might come up with routing?  My biggest concern is
>routing area, it appears that these will use less routing area than
>QFP packaging with the same main package and shorter leads.

Yes, generally less routing area, at least assuming relatively fine vias
where you might have to unscramble the leads.

>Can these be hand assembled? TI seems to think so, hence the question.

Sure.. you may want to use a footprint that has pads that extend
beyond the package for ease of assembly.

You might also want to ask your assembly house for opinions, given the
parameters (hand assembly quantities etc.)

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



2008\04\23@163520 by Brent Brown

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> >Can these be hand assembled? TI seems to think so, hence the question.
>
> Sure.. you may want to use a footprint that has pads that extend
> beyond the package for ease of assembly.

I did a few 28 pin QFN PIC's by hand (solder paste and iron) and it went smoother
than some of my TQFP attempts. My PCB pads were relatively short, and there was
just enough "lead" going up the side of the QFN package to make a nice little fillet.
Pad to pad bridges were easy to remove with solder wick - much harder with TQFP
as the solder between the longer leads and can be more difficult to remove.

For production runs my QFN's have been reflow soldered and have also worked out
fine, as they should. Presently though I have a design with a mix of SMD and PTH
parts on opposite sides of the PCB and my manufacturer is looking at the possibility
of wave soldering the QFN. They are going to run a few test boards with the board
rotated so the QFN package is offset 45 degrees to the direction of travel ~
hopefully the solder will drag away from the pads and not leave any bridges.

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  .....brent.brownKILLspamspam@spam@clear.net.nz


2008\04\23@180712 by Funny NYPD

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what's the Pitch of your QFN and TQFP?
We got the experience right on the opposite side. We found TQFP is lot of easier to handle for both Hand-solde and machine reflow. The quality control and inspection on QFN packages are challenge job.

The QFN package we are using has a pitch of 0.5mm, and the TQFP we used including the following pitches: 0.8mm, 0.65mm, and 0.5mm.
Regards,

Funny N.
Au Group Electronics, New Bedford, MA, http://www.AuElectronics.com

{Original Message removed}

2008\04\23@190033 by Brent Brown

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My comparison was with:

PIC16F886, QFN28, 0.65mm pitch
PIC18F8527, TQFP80, 0.5mm pitch

I guess there are a whole lot of variables that could come into play here and affect
results... for me it was hand soldering iron, solder paste placed by hand for TQFP,
solder wire for QFN, parts placed by hand, QFN stuck down with double sided tape
to hold it in place.

On 23 Apr 2008 at 15:06, Funny NYPD wrote:

{Quote hidden}

> {Original Message removed}

2008\04\24@175033 by Jesse Lackey

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Hi - I've done a bunch, hand soldered with wire solder, no problems.
I suggest using a flux pen like Kester #186.  I soldered them the same
way as tqfp: use flux pen on pcb pads, tack the chip down on corners,
put more flux down, then solder "pins" by just sweeping solder across
them.  Fix any bridges with solder braid.

They actually go faster than tqfp, since the solder "sweep" is really
quick once you get the hang of it.

Also - sometimes the QFN bottom pad must be connected to ground,
sometimes optional, but it is there for mechanical strength.  I put a
50mil via in the pad so I can solder it down from the backside with fine
tip soldering iron.

Good luck!
J


Stephen R Phillips wrote:
{Quote hidden}

2008\04\24@210356 by Xiaofan Chen

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On 4/25/08, Jesse Lackey <jsl-mlspamKILLspamcelestialaudio.com> wrote:
> Hi - I've done a bunch, hand soldered with wire solder, no problems.
> I suggest using a flux pen like Kester #186.  I soldered them the same
> way as tqfp: use flux pen on pcb pads, tack the chip down on corners,
> put more flux down, then solder "pins" by just sweeping solder across
> them.  Fix any bridges with solder braid.
>
> They actually go faster than tqfp, since the solder "sweep" is really
> quick once you get the hang of it.
>
> Also - sometimes the QFN bottom pad must be connected to ground,
> sometimes optional, but it is there for mechanical strength.  I put a
> 50mil via in the pad so I can solder it down from the backside with fine
> tip soldering iron.
>

Interesting, your idea is exactly the same as Leon Heller in this
Microchip forum thread.
http://forum.microchip.com/tm.aspx?m=327590

I am not a real hobbyist since I do not build board at home
(normally I will buy the demo boards instead) and I have
not designed any boards. But occassionally I need to do
rework on the QFN parts. The problem seems that I do not
have a steady enough hand.

There is also stability issues. I have done several rework
boards this time (QFN 6 with two center pads, but there is no
via since this is meant for reflow and not manual rework) and
some of them do not work well after a while. I use flux pen
as well and I use Hakko 850 hot air station and Hakko 936
soldering station as well as Hakko Solder Wick.


Xiaofan

2008\04\25@034905 by Vasile Surducan

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On 4/25/08, Jesse Lackey <.....jsl-mlKILLspamspam.....celestialaudio.com> wrote:
>
> Also - sometimes the QFN bottom pad must be connected to ground,
> sometimes optional, but it is there for mechanical strength.  I put a
> 50mil via in the pad so I can solder it down from the backside with fine
> tip soldering iron.


I'm curently using QFN with various pitch. Conection  the thermal pad
to the ground (specified on some datasheets optional indeed) is a
MUST. This will forgive you for any headache. For example on such
devices like USB3300
http://www.smsc.com/main/catalog/usb3300.html
the thermal pad has also electrical connections. A missing ground
connection to this pad keeps me busy for a few days...
You don't need a large via on the thermal pad (this is the way Maxim
is designing RF eval boards), also a few small vias are OK.

Vasile

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