24 Dye & Pry Testing This is a quick/inexpensive way to look for cracked or non-wetted BGA joints. Allows for simultaneous inspection of all of the joints at once. Materials and equipment needed are readily available
25 Dye & Pry Test Procedure Cut out device to be tested from the PCB Clean flux from under device and bake dry Immerse part in Dykem Red fluid under partial vacuum Shake off excess dye and bake dry Pry off BGA using pliers and/or vise and screwdriver Inspect for any dye on separated joints
36 Thermal Fatigue When the assembly is temperature or power cycled the different materials in the attach want to expand/contract according to their CTEs. The attach material is (usually) the weakest point in the assembly so it is expected to absorb the stresses of thermal mismatch by yielding in creep. The amount of creep an attach can endure is limited, then it will begin to crack.
41 Black Pad failure This only occurs on Electroless Nickel, Immersion Gold (ENIG) finished devices & boards: ENIG has come into wide use with the advent of RoHS and the lead- free solders The ENIG process actually corrodes the top layer of the electroless nickel-phosphorous as the gold is deposited in a displacement reaction This displacement reaction concentrates the phosphorous in the upper nickel layer right under the gold, and sometimes gets out of control Normal electroless nickel will have 8-12% P, but black pad regions can have up to 30% P! During soldering the very thin gold layer dissolves instantly leaving the solder on top of the corroded, high P, nickel layer. This can result in dewetting and/or poor solder joint strength When the solder joints fail, the corroded nickel layer is exposed and it is usually black in appearance; hence the name…