Hi Kevin

Commonly QFN's or DFN's don't have plating on the lower edge of the pad
(just copper left from where the pads are singulated after plating).
Depending on the copper wetting, there may or may not be a true toe fillet
formed.

Top of pad
______________
              |
              | <- plated from here up
             /
             ' <- just copper from here down
_____________'
     ^
     |
Bottom of pad, plated

To make matters worse, some packages have the pad edge actually enclosed by
the encapsulant. In this case it is better if the footprint does not have
any extension for a toe fillet, else wise the plastic sits on paste and
encouragess a weak hourglass fillet to form.

There are many advantages from micro lead frame packages, but joint
inspection ain't one of them! And as for how to clean out flux from under
them, if anyone knows a way then please tell...

<http://www.amkor.com/products/notes_papers/MLFAppNote.pdf>
<http://www.carsem.com/services/Drwgs&Data/CSM-MLP%20apps%20note-4-23-2002-3
00dpi.pdf>
<http://www.national.com/an/AN/AN-1187.pdf>

Best Regards

David Greig
______________________________
GigaDyne Ltd
Buchan House
Carnegie Campus
Dunfermline KY11 8PL
United Kingdom
t: +44 (0)1383 624 975
http://www.gigadyne.co.uk
______________________________



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Jaworenko
Sent: 01 December 2004 14:44
To: [log in to unmask]
Subject: [TN] Help, Help, I have a QFN Package I don't know what to do!

G'day Everyone.

        Well as the subject states we are currently running a prototype
assembly with a new package style to me, a QFN (Quad Flat No-lead). I had to
look that one up myself.

        The problem is when we were trying to reflow the part, the solder
joint looks very poor, with little to no solder seen on the edge of the
component lead and the pad on the PCB, or a bubble of solder seen on end of
the component between the edge of the component lead and the pad of the PCB.

        I'm currently setting up to X-ray the components to see if the foot
actually has a good solder joint underneath the component, where the lead
has been curled around the component, but has anyone else had any dealings
with this particular component type before and would be willing to share?

        I looked up the component manufacture's website and they show that
this component has a required peak temperature of 235 (+5/-0) degrees C.
That seems like a lot of heat for a non lead-free component.

        Feel free to email me offline if anyone likes.

Thanks in advance.

Kevin Jaworenko
Manufacturing Engineering Technologist
Vansco Electronics LP
(204) 453 - 3339 ext. 622
(204) 453 - 3663 FAX
[log in to unmask]


---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask] with following text in the
BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet
NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send
e-mail to [log in to unmask]: SET Technet Digest Search the archives of
previous posts at: http://listserv.ipc.org/archives Please visit IPC web
site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
--
Virus scanned by Lumison.

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------