Dear Mark
As we are a CEM we get every conceivable method.
The only method that I have seen give a difficulty is where open vias go
to a solderable plane on the bottom. This seems to introduce additional
forces into the tug of war between the top and bottom faces and swings
the tug in favour of the solder being stolen by the bottom side.
In the past we have done the arithmetic to ensure that enough paste is
applied to fill the vias.
Regards
Rex

Rex Waygood
Technical Manager
 
Hansatech EMS provides value manufacturing through engineering and
quality
 
Hansatech EMS Limited
Benson Road
Nuffield Industrial Estate
Poole
Dorset
BH17 0RY
 
+44 (0)1202 338200




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mark Larson
Sent: 31 August 2011 20:52
To: [log in to unmask]
Subject: [TN] QFN with solder slug

I am curious how others are handling these parts for soldering. Do you
leave the thermal vias in the slug covered or uncovered with solder
mask? Do you fill with anything? What size hole on a 62 mil board? Tie
to all GND planes or just the back side? Thermal relief the via or bury
it in the plane?

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