Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Intermetallics

Ben Salisbury

#14662

Intermetallics | 18 August, 1998

Question: If a PCB and the lands of a part both had electroless plating, would there be a higher tendancy for intermetallics to form in and on the solderjoint...versus just the PCB or Just the part being plated? I'm currently running into this problem with a plated PCB, and a resonator w/ plated lands. All of the other parts on the panel do not have intermetallic formations. -Ben

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Earl Moon

#14663

Re: Intermetallics | 18 August, 1998

| Question: | If a PCB and the lands of a part both had electroless plating, would there be a higher tendancy for intermetallics to form in and on the solderjoint...versus just the PCB or Just the part being plated? | I'm currently running into this problem with a plated PCB, and a resonator w/ plated lands. All of the other parts on the panel do not have intermetallic formations. | -Ben

Notwithstanding the tin immersion process to coat component leads and the oxidation taking place thereon, it has been discussed that various, and excessive intermetallic formations can be effected in solder joints. The debate rages over immersion process chemistries and how various components affect solder joint quality relative to the intermetallics formed. It also is said that electroplating chemistries provide less risk to adverse intermetallic formations. Also, it has been known for some time, the homogeneous surface of, say, tin/lead electroplated parts having be reflowed offer the best solderability. Again, the definition of soldering is the joining of to metal surfaces, using a specified solder medium, without requiring difussion or intermetalic formations. It all comes down to what's in the chemistries used to coat surfaces and what must be done to make them wet as to whether, and how much, intermetallics will be formed. And on it goes. What about the deleterious effects of two much intermetallics? How much is too much? Etc.. Earl Moon

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