Sitting in on some J-STD-033 meetings, I've heard of studies where baking with vacuum or nitrogen wasn't very effective.  The theory is that water molecules inside the package don't have any way to sense the conditions outside the package.  Higher temperature is necessary to get the water molecules bouncing around more energetically, and that's how they leave.

You're trying to move off of equilibrium so that moisture leaves faster than it's being absorbed back in.  So low external RH prevents moisture from moving back into the package, but doesn't help entrapped moisture leave any faster.

-Joe

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Post, Scott E
Sent: Wednesday, July 21, 2010 10:12 AM
To: [log in to unmask]
Subject: [TN] Baking in tape & reel

I have some BGAs (not active - just daisy chained with dummy die) in tape & reel that I need to bake.  I know I could remove them and put them in trays for baking, but for various reasons I'd like to avoid
this.   Based on the component thickness, JEDEC recommends 13 days at
40C.   My main concern is that heat will effect the glue on the cover
tape and make the reel a pain to use on an SMT feeder.   I have an oven
that has a nitrogen feed and a vacuum pump, so either inerting or vacuum is an option.  Has anyone played  with using lower temps (30C?) but either inerting or pulling a vacuum?  I'm concerned that a vacuum may collapse the cover tape into the pockets and pull the glue loose.

 

I don't necessarily need to reset the moisture clock to 0 either - I just need to reduce the warpage.  These are 0.4 mm pitch and I'm getting shorting in the corners.  I ran Thermoire on samples before and after a 125C overnight bake and the unbaked samples turned into potato chips above 200C.  The corners are warping 200 microns towards the board.  The baked samples stay flat during reflow.  I'm re-introducing moisture to the baked samples and I'll run Thermoire again to make sure moisture caused the warpage rather than some uncured material that I cured during the 125C bake.

 

Scott Post
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road 
Kokomo, Indiana    46904-9005 
765-451-2983 (Phone)
765-451-0287 (FAX) 


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