Process for preparing solderable integrated circuit lead frames by plating with tin and palladium

Claim 2

A process for preparing a solderable lead frame having a multiplicity of leads, said lead frame having an external region and an internal region, the process comprising the steps of: tin plating the multiplicity of leads on a base lead frame made from a base lead frame material to deposit tin on the external region while leaving the internal region unplated; and palladium plating a portion or all of the base lead frame after the step of tin plating whereby the external region coated with tin and at least a portion of the unplated internal region are coated with palladium.

Claim 3

A process as recited in claim 1 wherein said step of tin plating includes plating a tin alloy having eutectic points between about 180 degrees centigrade and 300 degrees centigrade.

Claim 4

A process as recited in claim 1 wherein said step of tin plating includes plating a tin alloy including one or more elements chosen from a group consisting of antimony, arsenic, bismuth, cadmium, gallium, gold, indium, iridium, lead, platinum, rhodium, ruthenium, silver, thallium, and zinc.

Claim 5

A process as recited in claim 1 wherein said step of palladium plating includes flood plating the entire base lead frame.

Claim 6

A process as recited in claim 1 wherein said base lead frame is supplied for plating as part of a lead frame ribbon.

Claim 7

A process as recited in claim 1 further comprising the step of plating the base lead frame with a diffusion barrier material before said step of tin plating whereby said base lead frame material is substantially prevented from diffusing into said tin.

Claim 8

A process as recited in claim 6 wherein said base lead frame contains copper and wherein said step of base plating includes a step of nickel plating.

Claim 9

A process as recited in claim 7 wherein said base lead frame contains copper and wherein said step of base plating includes a step of cobalt plating.

Claim 10

A continuous method for plating a base lead frame made from a base lead frame material and having an external region and an internal region to form a solderable lead frame, the method comprising: a first step of electroplating tin or tin alloy on the base lead frame in a first reaction chamber through which the base lead frame is passed to deposit tin on the external region while leaving the internal region unplated on the base lead frame; and a second step of electroplating palladium on the base lead frame in a second reaction chamber through which the base lead frame is passed to form a palladium coating on the external region coated with tin and at least a portion of the unplated internal region wherein the first and second steps are part of the same continuous process.

Claim 11

A continuous method for plating a base lead frame made from a base lead frame material and having an external region and an internal region to form a solderable lead frame, the method comprising: a first step of electroplating tin or tin alloy on the base lead frame in a first reaction chamber through which the base lead frame is passed to deposit tin on the external region while leaving the internal region unplated on the base lead frame; and a second step of electroplating palladium on the base lead frame in a second reaction chamber through which the base lead frame is passed to form a palladium coating on the external region coated with tin and at least a portion of the unplated internal region wherein the first and second steps are part of the same continuous process.

Claim 12

A method as recited in claim 9 wherein said base lead frame is provided to the continuous process as part of a lead frame ribbon.

Claim 13

A method as recited in claim 9 wherein said tin-alloy has a eutectic point between about 180 degrees centigrade and 300 degrees centigrade.

Claim 14

A method as recited in claim 9 wherein said tin alloy comprises tin alloyed with one or more elements chosen from a group consisting of antimony, arsenic, bismuth, cadmium, gallium, gold, indium, iridium, lead, platinum, rhodium, ruthenium, silver, thallium, and zinc.

Claim 15

A method as recited in claim 10 wherein said first step is conducted in a spot plating reactor and wherein said second step is conducted in a flood plating reactor.

Claim 16

A method as recited in claim 13 wherein said flood plating reactor deposits said palladium on both said external and internal regions of the leads.

Claim 17

A process as recited in claim 9 further comprising the step of base plating with a diffusion barrier material before said first step whereby said base lead frame material is substantially prevented from diffusing into said tin or said tin alloy.

Claim 18

A process as recited in claim 15 wherein said base lead frame contains copper and wherein said step of base plating includes a step of nickel plating.

Claim 19

A process as recited in claim 15 wherein said base lead frame contains copper and wherein said step of base plating includes a step of cobalt plating.