Trying to heat flex to the temperature required to melt solderballs on the other side, I am not sure if that can be done using laser, nor would it be feasible due to the amount of time required versus convection reflow.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Thursday, February 04, 2010 8:21 AM
To: [log in to unmask]
Subject: Re: [TN] Laser soldering of BGA

Technos,

There are 2 main ideas I can gather from your answers:

1. Why do I bother with laser when I could reflow? Well, as I said, reflow seems to warp either the component or the PCB and having no idea about laser soldering myself, I thought it would be a good idea to inquire. Since it seems to have no benefit, I believe I better get back to reflow. But not before asking another one: the BGA is soldered onto flex that is backed by a 12 mil rigid something; are there lasers that could solder from the bottom, through the substrate, rather than through the part, thus minimizing the heat seen by the assembly?

2. Steve K, could you please elaborate regarding the metal stiffener vs. FR-4. To my surprise, it seems that brass stiffeners yield better results than FR-4 indeed; shouldn't they give a bigger CTE mismatch?

Thanks,

Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] 
W | www.digico.cc

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