As young David has said we have produced both Inspection Posters and a
booklet both available from the SMTA and IPC bookstores. Produced as people
like or need some reference.
The only real data I have seen while running my QFN Workshops was a decrease
in thermal performance at 50% plus voiding. Obviously there are loads of
factors.
David and I are hoping to complete some trial on void size and stand off
height which also links to open connections.
Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
Tel: (44) 1245 351502
Fax: (44) 1245 496123
Mobile: 07860 775858
www.ASKbobwillis.com
New Bob Willis "Printed Board Inspection & Quality Control Workshop" 3rd
September www.ASKbobwillis.com/PCBworkshop.pdf
Book your place on Bob's "Step by Step Failure Analysis Workshop" 11th
September www.ASKbobwillis.com/faworkshops.pdf
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: 29 August 2008 09:33
To: [log in to unmask]
Subject: Re: [TN] LGA/QFN voids %
I have just had to deal with a video chip which gets exceedingly hot
where the part is qualified down to 50% coverage/void of the thermal
pad.
If a standard comes about then the standard having a tighter requirement
than the part is qualified for by the manufacturer doesn't make much
sense to me.
Regards
Rex
:-)
Rex Waygood
Technical Manager
PartnerTech Poole Ltd
Benson Road
Poole
Dorset BH17 0RY
United Kingdom
Tel: +44 (0)1202 674333
Fax: +44 (0)1202 678028
DDI: +44 (0)1202 338222
Mob: +44 (0)7887 997403
[log in to unmask]
www.PartnerTech.co.uk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bernard, David
Sent: 29 August 2008 09:08
To: [log in to unmask]
Subject: Re: [TN] LGA/QFN voids %
There are no standards/guidelines at this time, although the IPC has
recently convened a task group to put one together along the lines of
the IPC7095 for BGAs.
Bob Willis and I have advocated a maximum of 20% voiding (whether by a
single void or multiple voids) in either the central or edge
terminations when viewed by x-ray inspection. However, some people may
define a higher total percentage voiding as acceptable (say 30%,
especially within the central termination) but with the extra proviso
that no single void should exceed perhaps 5 or 10%. This appears to be
more of concern for devices that require the ability to dissipate a
larger quantity of heat and the presence of any large voids may affect
this efficiency.
At the end of the day, however, without the any formal limit defined in
IPC610D, or other documents, then I would suggest that you should
negotiate an acceptable limit between yourself and your customer.
David
Dr. David Bernard
Product Manager X-ray Systems
Dage Precision Industries
Rabans Lane
Aylesbury
Buckinghamshire
HP19 8RG
United Kingdom
Tel: +44 1296 317800
Mob:+44 7796 993391
E-mail: [log in to unmask]
www.dage-group.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tan Geok Ang
Sent: 29 August 2008 02:32
Subject: LGA/QFN voids %
Hi All,
Need you expertise in advising the maxi. allowable void %
in
LGA and QFN. Does any standard state this requirement?
Thank and have a nice day!
Regards
GA Tan
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