I agree Rex, For QFN parts the issue is generally thermal and /or signal to ground noise related rather that "mechanical" or "current capacity" related. They are indeed interesting devices for low I/O applications. I have been using them in designs for around 5 or 6 years now with no issues although a high res X-ray always comes in handy.....8-) John John Burke (408) 515 4992 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood Sent: Friday, August 29, 2008 1:33 AM 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! 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