OK, OK. 672 ball BGA.
The pcbs are PC Card bus size and are .015 thick. There are 3 on a panel with about 1/2" between and rails.
The aluminum plates are about 3" by 7". There are 3 cutouts which allow for the parts from either side to protrude during palcement and reflow. The panels are printed first then placed into the AL bottom plate. An AL top plate is placed on top and 6 nuts clamp it tightly to the bottom plate thus holding the pcb flat. The plates/pcb are then placed on conveyor for placement and reflow.
We print paste for everyting but the BGA. We use a brush to apply the sticky flux. Therefore I can't say that the flux application is controlled very well.
The BGA is actually 1 mm pitch, sorry. Balls are .024D and the pads on the pcb are .0157.
We tried one stencil, 5 mil thick with .016 aps. After consulting with the stencil house yesterday, we are ordering a 4 mil stencil with 3 patterns, 1 with .008 aps, 1 with .010 aps and the third with .012 aps. We'll have that in a couple of days.
The pads are .016, round. The plating is white tin.
Further FYI, we have a BTU VIP 70 with 5 zones. Due to the expense of the BGA (500.00 ea.) the customer was reluctant to allow us to do a destructive profile. Now, they are giving us a couple of 3 pcb panels and 3 parts. once we get the stencil we will drill holes in the pb and bring 2 thermocouples up under each BGA on each PCB.
We use a CircuitMaster Designs profiler with 6 thermocouples.
Typical profiles we run have temp ramp rates of 1.25 to 2.00 C/second.
Now, what are your thoughts?
Thanks in advance for your consideration.
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