Gregg,

what's the issue(s). We have been using QFNs for a long time and without 
significant problems. However, as a microwave application guy (sometimes) 
I'll give you  two winks:

1. Have a hard look at your supplier's QFN center pad finish!

2. Correct solder paste volume for the center pad!

Here is a good microwave page, if you don' t already have it.

http://www.mwee.com/202803709


By the way, it's remarkable with the engineering life. Bumble-bees can' t 
fly according to technical calculations. But she doesn' know that and is 
flying since millions of years without any improvements. QFNs may be the 
same ?

Inge

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> To
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> Subject
> [TN] Use of QFN devices in high reliability applications
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> Our team is working on several new electronic devices whose application is
> primary, flight critical hardware for commercial aircraft.
>
> Our initial component selection includes many QFN packaged devices
> (leadless, bottom side termination only) which will be mounted on .063"
> FR4 boards using SN63.  The devices range from 20 to 44 terminations.
>
>>From studies that are available on the web, a picture has emerged that QFN
> packages have reduced long term solder joint reliability when compared
> with leaded or some of ball grid array devices.  Board thickness, flexing
> and whether the device has a central solderable heat sink seem to have a
> significant affect on reliability.  Problem is there are no absolute
> numbers, so for critical applications it seems that thorough testing is
> required.  We'd rather not wait until the end of a lengthy test regimen to
> find we've gone down the wrong path.  Is there newer information
> abbailable?   Two of the studies stated that further testing was being
> performed to support the reliability requirements for aerospace and other
> high-rel applications however I cannot find any updated information on the
> web.
>
> We have decided to replace several of the QFN's with leaded devices,
> however there are no direct crosses for 3 of the devices. One of them will
> require a number of components to create the same function; possibly an
> additional circuit card.
>
> Is anyone aware of information or recommendations that would be useful for
> our assessment?  Is there any specific information that would drive us to
> use or not use them?
>
> Thanks for your help
>
> Gregg
>
>
>
>
>
>
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