Surface Mount assemblies IPC Standards

Could somebody tell me what means Leaching, ie: "Leaching of terminal end face exposing the ceramic"?

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| Could somebody tell me what means Leaching, ie: "Leaching of terminal end face exposing the ceramic"? | Roberto: Leaching, according to the SMTnet Library of Terms:

Leaching. Dissolution of a metal coating into liquid solder. Nickel barrier under-plating prevents the over-plating (usually gold or silver) from leaching into the copper base.

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| | Could somebody tell me what means Leaching, ie: "Leaching of terminal end face exposing the ceramic"? | | | Roberto: Leaching, according to the SMTnet Library of Terms: | | Leaching. Dissolution of a metal coating into liquid solder. Nickel barrier under-plating prevents the over-plating (usually gold or silver) from leaching into the copper base. | Roberto,

This is sometimes referred to as migration but I'm not sure that it's exectly the right term. The reason for the leaching / migration is to do with grain structures of metals, as in the gap's and size of the atoms. Thing's like gold or silver are smaller than your tin / lead so can fit into the spaces between the tin/lead atom's hence it migrates or leaches. In the big mechanical world I guess it's the same as slip but on an increadibly small scale. There reason for the addition of a 2% silver into the solder when processing gold or silver boards / components is to effectively plug the gap's in the tin / lead microstructure and stop the migration.

hope this help's..unless of course I got it wrong then all I can say is woops and it's late!

JohnW

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| | | Could somebody tell me what means Leaching, ie: "Leaching of terminal end face exposing the ceramic"? | | | | | Roberto: Leaching, according to the SMTnet Library of Terms: | | | | Leaching. Dissolution of a metal coating into liquid solder. Nickel barrier under-plating prevents the over-plating (usually gold or silver) from leaching into the copper base. | | | Roberto, | | This is sometimes referred to as migration but I'm not sure that it's exectly the right term. | The reason for the leaching / migration is to do with grain structures of metals, as in the gap's and size of the atoms. Thing's like gold or silver are smaller than your tin / lead so can fit into the spaces between the tin/lead atom's hence it migrates or leaches. In the big mechanical world I guess it's the same as slip but on an increadibly small scale. | There reason for the addition of a 2% silver into the solder when processing gold or silver boards / components is to effectively plug the gap's in the tin / lead microstructure and stop the migration. | | hope this help's..unless of course I got it wrong then all I can say is woops and it's late! | | JohnW | Roberto, if what you are saying is that this is causing defects in your process - look for excessivly high temperatures or too long a time over liquidus. These conditions speed up the leaching/migration process tremendously. Or course, it could just be lousy components. John Thorup

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| | | Could somebody tell me what means Leaching, ie: "Leaching of terminal end face exposing the ceramic"? | | | | | Roberto: Leaching, according to the SMTnet Library of Terms: | | | | Leaching. Dissolution of a metal coating into liquid solder. Nickel barrier under-plating prevents the over-plating (usually gold or silver) from leaching into the copper base. | | | Roberto, | | This is sometimes referred to as migration but I'm not sure that it's exectly the right term. | The reason for the leaching / migration is to do with grain structures of metals, as in the gap's and size of the atoms. Thing's like gold or silver are smaller than your tin / lead so can fit into the spaces between the tin/lead atom's hence it migrates or leaches. In the big mechanical world I guess it's the same as slip but on an increadibly small scale. | There reason for the addition of a 2% silver into the solder when processing gold or silver boards / components is to effectively plug the gap's in the tin / lead microstructure and stop the migration. | | hope this help's..unless of course I got it wrong then all I can say is woops and it's late! | | JohnW | John: Two things:

1 Leaching. I believe the leaching applies to liquid solder and is applied inaccurately to metallurgical effects, like diffusion, that occur after the solder has solidified. 2 Sn62Pb36Ag2. The original intent of 2% Ag addition to solders was to minimize the leaching of Ag and other noble metal terminations of chip caps and resistors into the solder joint by reducing the Ag concentration gradient and thus slowing down the noble metal dissolution rate.

� Now that most chip device manufactures offer Ni barriers in their termination metallurgy, Sn62 seems redundant. � Good theory, but it never worked in practice, because at reflow the solubility of Ag in molten Sn/Pb solder is beyond the 2 (weight)% contained in Sn62Pb36Ag2.

TTYL

Dave F

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| | | | Could somebody tell me what means Leaching, ie: "Leaching of terminal end face exposing the ceramic"? | | | | | | | Roberto: Leaching, according to the SMTnet Library of Terms: | | | | | | Leaching. Dissolution of a metal coating into liquid solder. Nickel barrier under-plating prevents the over-plating (usually gold or silver) from leaching into the copper base. | | | | | Roberto, | | | | This is sometimes referred to as migration but I'm not sure that it's exectly the right term. | | The reason for the leaching / migration is to do with grain structures of metals, as in the gap's and size of the atoms. Thing's like gold or silver are smaller than your tin / lead so can fit into the spaces between the tin/lead atom's hence it migrates or leaches. In the big mechanical world I guess it's the same as slip but on an increadibly small scale. | | There reason for the addition of a 2% silver into the solder when processing gold or silver boards / components is to effectively plug the gap's in the tin / lead microstructure and stop the migration. | | | | hope this help's..unless of course I got it wrong then all I can say is woops and it's late! | | | | JohnW | | | John: Two things: | | 1 Leaching. I believe the leaching applies to liquid solder and is applied inaccurately to metallurgical effects, like diffusion, that occur after the solder has solidified. | 2 Sn62Pb36Ag2. The original intent of 2% Ag addition to solders was to minimize the leaching of Ag and other noble metal terminations of chip caps and resistors into the solder joint by reducing the Ag concentration gradient and thus slowing down the noble metal dissolution rate. | | � Now that most chip device manufactures offer Ni barriers in their termination metallurgy, Sn62 seems redundant. | � Good theory, but it never worked in practice, because at reflow the solubility of Ag in molten Sn/Pb solder is beyond the 2 (weight)% contained in Sn62Pb36Ag2. | | TTYL | | Dave F | Dave,

the phrase OOPS spring to mind, oh well it was late after all

John

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| | | | | Could somebody tell me what means Leaching, ie: "Leaching of terminal end face exposing the ceramic"? | | | | | | | | | Roberto: Leaching, according to the SMTnet Library of Terms: | | | | | | | | Leaching. Dissolution of a metal coating into liquid solder. Nickel barrier under-plating prevents the over-plating (usually gold or silver) from leaching into the copper base. | | | | | | | Roberto, | | | | | | This is sometimes referred to as migration but I'm not sure that it's exectly the right term. | | | The reason for the leaching / migration is to do with grain structures of metals, as in the gap's and size of the atoms. Thing's like gold or silver are smaller than your tin / lead so can fit into the spaces between the tin/lead atom's hence it migrates or leaches. In the big mechanical world I guess it's the same as slip but on an increadibly small scale. | | | There reason for the addition of a 2% silver into the solder when processing gold or silver boards / components is to effectively plug the gap's in the tin / lead microstructure and stop the migration. | | | | | | hope this help's..unless of course I got it wrong then all I can say is woops and it's late! | | | | | | JohnW | | | | | John: Two things: | | | | 1 Leaching. I believe the leaching applies to liquid solder and is applied inaccurately to metallurgical effects, like diffusion, that occur after the solder has solidified. | | 2 Sn62Pb36Ag2. The original intent of 2% Ag addition to solders was to minimize the leaching of Ag and other noble metal terminations of chip caps and resistors into the solder joint by reducing the Ag concentration gradient and thus slowing down the noble metal dissolution rate. | | | | � Now that most chip device manufactures offer Ni barriers in their termination metallurgy, Sn62 seems redundant. | | � Good theory, but it never worked in practice, because at reflow the solubility of Ag in molten Sn/Pb solder is beyond the 2 (weight)% contained in Sn62Pb36Ag2. | | | | TTYL | | | | Dave F | | | Dave, | | the phrase OOPS spring to mind, oh well it was late after all | | John | | Hey guy, you weren't that far off base.

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| | Could somebody tell me what means Leaching, ie: "Leaching of terminal end face exposing the ceramic"? | | | Roberto: Leaching, according to the SMTnet Library of Terms: | | Leaching. Dissolution of a metal coating into liquid solder. Nickel barrier under-plating prevents the over-plating (usually gold or silver) from leaching into the copper base. |

Has anybody out there had experience stencil printing glue ?

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