Bobby / Paul,
I am going to give you guys my business, economic and technical opinions and guidelines and want you guys to handle the rework project accordingly.
Here is where some process engineering work is needed. We have
identified a very clear issue with the inconsistent solder on the
Ibook video BGA. I agree with your analogy of both concave and convex
solder joints except that I dont believe solder is migrating into any
vias. (Unless the Xray shows that the vias between the solder balls
have solder in them). I havent looked at any, but rarely does the mask
breakdown unless it has been wicked over once or twice during a
re-surface process. I believe that this is the result of inconsistent
paste deposition either from a poorly controlled printing process
OR - CHECK OUT THIS CONCEPT: I have discovered that ATI Radeon
Mobility video chips on a variety of products have had this
intermittent fractured solder joint problem. It is possible (not
certain) that the packaging engineers at ATI specified undersized
apertures for their recommended solder paste file.
I would like to have one of you locate the datasheet for the ATI Radeon
Mobility Chip for two reasons: 1) I would like to review the
recommended aperture sizes for solder paste deposition 2) I need to get
the mechanicals for possibly using preforms to reball.
I have probably between 85-95% success rate by just reflowing the BGA
for the customer. I am confident this rework will give them 1-2 years,
and possibly as much functional life out of their laptop as they had
before it broke. It is, as mentioned curing the symptom (broken
solderjoints) but not the cause (inconsistent solder joint size).
I dont think we're going to get into re-balling these unless I find there is a market for it which I will research. I may reball the Ibook that is there with Bridges on it just to do an analysis /reliability test. Anyway.....if a complete reball was the answer to both the symptom and the cause, the customers threshold of pain is $75 and I actually see our cost with burden rate around $100. So we would need to research some alternative to the plate reballing method (possibly use pre-forms).
Regardless of whether we reflow or reball, we need to verify that the
new rework station has the correct parameters entered. You need to get
a 5mil thermocouple from the SlimKic box in the SMT area. The
thermocouple that is currently plugged in to the BGA 3000 is too short.
Then slide the thermocouple beneath the BGA on a scrap motherboard,
(use the one with the fried components on the end of it). If you want
to get even better contact there is a thermally conductive adhesive the
SMT area for attaching thermocouples. I believe there are reference
profiles in the Slimkic manuals for 63/37 solder paste. If not, here is
a reference: http://media.maxim-ic.com/images/appnotes/3377/3377Fig06.gif
--
Tom McCarthy
First Phase Technologies
2640 W Medtronic Way
Tempe, AZ 85281
480-967-1100 W
480-283-3205 C
