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Leaching

Leaching - Apr 25, 2003 by razor  

Leaching - Apr 25, 2003 by davef  

Leaching - Apr 26, 2003 by

Leaching - Apr 28, 2003 by razor  

Leaching - Apr 29, 2003 by davef  

Leaching - Apr 29, 2003 by davef  

Leaching - May 02, 2003 by Kris  

razor

#24298

Leaching | 25 April, 2003

Please explain the phenomenon of solder leaching on SMD end caps. What is the root cause? What is the best control method?

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#24303

Leaching | 25 April, 2003

Leaching. Dissolution of a metal coating into liquid solder. Leaching applies to liquid solder and, at times, is applied inaccurately to metallurgical effects, like diffusion, that occur after the solder has solidified.

Please help us understand your situation better. * Base material of your end caps? * Solderability protection of the base material in the end caps? * Solder being used? * etc?

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Iman

#24305

Leaching | 26 April, 2003

no S**t, I was going into SMTnet to post a question, on :

1) what is the actual "physics" behind "Leaching" defect? what is the accurate desciption to define this defect? how to eliminate the general causes to this defect? If encounter, what work process/how to get concession waiver to IPC-A-610C acceptance spec?

2) what is the actual "physics" behind "Metallization" defect? what is the accurate description to define this defect? how to elinimate the general causes to this defect? If encounter, what work process/how to get concession waiver to IPC-A-610C acceptance spec?

Looks like I was beaten to the punch?!?

Hope to hear from the experts soon.

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razor

#24334

Leaching | 28 April, 2003

Component: Termination (barrier) NI, 120/3.0 um Solder Plate (outer) 90% Sn, 10% Pb, 120/3.0 um

Solder: Multicore CR39, 95.5%Sn/3.8%Ag/.7%Cu @ 6mil

Flex PCB: Cu, Ni, Au .2m to .5m

Thanks

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#24341

Leaching | 29 April, 2003

With a nickel barrier and 'tin' plating, reconsider your reflow recipe to reduce the leaching of the termination into the solder during reflow. Points are: * In designing a reflow temperature recipe, it is important that the temperature be raised at least 20*C above the melting or liquidus temperature to ensure complete solder melting, flux activation, joint formation and the avoidance of cold melts. * The total time the parts are held above the melting point must belong enough to alloy the alloy to wet, to become homogenous and to level, but not enough to cause leaching of solder, metallization or flux charring. Reflow guidelines are: ** 270�C / 70 seconds max ** 250�C / 78 seconds max ** 230�C / 92 seconds max

Think about this, try soldering to the end cap plating, rather than trying to get the plating to melt in the solder. You do not need to melt a pure tin coating to get a good joint as pure tin will wet quite well.

[We know, We know. We have been arguing for a long time that you need to think about the alloy formed between the solder and the end cap plating, but we're taking a different tact.]

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#24343

Leaching | 29 April, 2003

Metallization failure. A defect such as voids, cracks, separations, depressions, notches or tunnels or any combination in the cross sectional reduction that is a basis for rejection.

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Kris

#24395

Leaching | 2 May, 2003

Hi

What is your reflow profile ? Try to limit exposure at parts with visible leaching to around 30 to 40 secs at around 235 to 240 deg

T

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