Method to form solder deposits on substrates
View Patent ↗Described is a method of forming a solder deposit on a substrate comprising the following steps i) provide a substrate that includes at least one inner contact area, ii) contact the entire substrate area including the at least one inner contact area with a solution suitable to provide a conductive layer on the substrate surface, iii) form a patterned resist layer, iv) electroplate a solder deposit layer containing a tin or tin alloy onto the inner contact area, v) remove the patterned resist layer, vi) form a solder resist layer having solder resist openings on the substrate surface.
1. A method of forming a solder deposit on a substrate comprising the following steps:
a. provide a substrate including a copper or copper alloy surface that includes at least one inner layer contact pad,
b. form an opening for the at least one inner layer contact pad extending through the copper surface,
c. contact the entire substrate surface including the opening and the at least one inner layer contact pad with a solution suitable to provide a conductive layer on the substrate surface,
d. deposit and pattern a resist layer whereby the at least one inner layer contact pad is exposed,
e. electroplate a solder deposit layer consisting of tin or tin alloy into the openings,
f. remove the resist layer,
g. remove the bare conductive layer which is not covered by a solder deposit layer and the copper or copper alloy surface beneath said conductive layer which is not covered by a tin or tin alloy layer by etching wherein the solder deposit layer 108 has the function of the etch resist,
h. apply a solder resist layer and form solder resist openings to expose the solder deposit layer.
2. The method according to claim 1 wherein in step d also openings for a metal resist are formed which are filled with a patterned metal resist layer by electroplating of tin or tin alloy in step e.
3. The method according to claim 2 wherein the additional process steps
g2 deposit a tin etch resist layer onto the solder deposit layer and remove layer and
g3 remove of the tin etch resist layer from the solder deposit layer are applied.
4. The method according to claim 1 wherein a metal resist layer is removed by etching.
5. The method according to claim 1 wherein an additional metal layer is deposited between step c. and step d. in claim 1 .
6. The method according to claim 1 wherein an additional metal layer is deposited between step d. and step e. in claim 1 .
7. The method according to claim 1 wherein an intermediate solder deposit top layer is deposited onto the solder deposit layer.
8. The method according to claim 1 wherein the conductive seed layer is selected from the group consisting of copper, nickel, silver, alloys thereof and multilayers of the aforementioned metals and alloys.
9. The method according to claim 1 wherein a reflow treatment is applied to the substrate having a solder deposit layer and a solder resist layer attached.
10. The method according to claim 1 wherein the inner layer contact pad 102 comprises a via or trench.
11. The method according to claim 1 wherein the substrate is a printed circuit board, an IC substrate or an interposer.
12. The method according to claim 2 wherein a metal resist layer is removed by etching.
13. The method according to claim 3 wherein a metal resist layer is removed by etching.