COATED WIRE

Abstract

A wire comprising a wire core with a surface, the wire core having a coating layer superimposed on its surface, wherein the wire core itself consists of: (a) pure silver consisting of (a1) silver in an amount in the range of from 99.99 to 100 wt.-% and (a2) further components in a total amount of from 0 to 100 wt.-ppm or (b) doped silver consisting of (b1) silver in an amount in the range of from >99.49 to 99.997 wt.-%, (b2) at least one doping element selected from the group consisting of calcium, nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount of from 30 to <5000 wt.-ppm and (b3) further components in a total amount of from 0 to 100 wt.-ppm, or (c) a silver alloy consisting of (c1) silver in an amount in the range of from 89.99 to 99.5 wt.-%, (c2) at least one alloying element selected from the group consisting of nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount in the range of from 0.5 to 10 wt.-% and (c3) further components in a total amount of from 0 to 100 wt.-ppm, or (d) a doped silver alloy consisting of (d1) silver in an amount in the range of from >89.49 to 99.497 wt.-%, (d2) at least one doping element selected from the group consisting of calcium, nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount of from 30 to <5000 wt.-ppm, (d3) at least one alloying element selected from the group consisting of nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount in the range of from 0.5 to 10 wt.-% and (d4) further components in a total amount of from 0 to 100 wt.-ppm, wherein the at least one doping element (d2) is other than the at least one alloying element (d3), wherein the individual amount of any further component is less than 30 wt.-ppm, wherein the individual amount of any doping element is at least 30 wt.-ppm, wherein all amounts in wt.-% and wt.-ppm are based on the total weight of the core, and wherein the coating layer is a double-layer comprised of a 1 to 1000 nm inner layer of gold and an adjacent 0.5 to 100 nm thick outer layer of palladium or a double-layer comprised of a 0.5 to 100 nm thick inner layer of palladium and an adjacent >200 to 1000 nm thick outer layer of gold.

Claims

1. A wire comprising a wire core with a surface, the wire core having a coating layer superimposed on its surface, wherein the wire core itself consists of: (a) pure silver consisting of (a1) silver in an amount in the range of from 99.99 to 100 wt.-% and (a2) further components in a total amount of from 0 to 100 wt.-ppm, or (b) doped silver consisting of (b1) silver in an amount in the range of from >99.49 to 99.997 wt.-%, (b2) at least one doping element selected from the group consisting of calcium, nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount of from 30 to <5000 wt.-ppm and (b3) further components in a total amount of from 0 to 100 wt.-ppm, or (c) a silver alloy consisting of (c1) silver in an amount in the range of from 89.99 to 99.5 wt.-%, (c2) at least one alloying element selected from the group consisting of nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount in the range of from 0.5 to 10 wt.-% and (c3) further components in a total amount of from 0 to 100 wt.-ppm, or (d) a doped silver alloy consisting of (d1) silver in an amount in the range of from >89.49 to 99.497 wt.-%, (d2) at least one doping element selected from the group consisting of calcium, nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount of from 30 to <5000 wt.-ppm, (d3) at least one alloying element selected from the group consisting of nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount in the range of from 0.5 to 10 wt.-% and (d4) further components in a total amount of from 0 to 100 wt.-ppm, wherein the at least one doping element (d2) is other than the at least one alloying element (d3), wherein the individual amount of any further component is less than 30 wt.-ppm, wherein the individual amount of any doping element is at least 30 wt.-ppm, wherein all amounts in wt.-% and wt.-ppm are based on the total weight of the core, and wherein the coating layer is a double-layer comprised of a 1 to 1000 nm inner layer of gold and an adjacent 0.5 to 100 nm thick outer layer of palladium or a double-layer comprised of a 0.5 to 100 nm thick inner layer of palladium and an adjacent >200 to 1000 nm thick outer layer of gold.

2. The wire of claim 1, wherein the wire has an average cross-section in the range of 50 to 5024 μm.sup.2.

3. The wire of claim 1, wherein the wire has a circular cross-section with an average diameter in the range of 8 to 80 μm.

4. The wire of claim 1, wherein the wire has a wire core diameter in the range of 10 to 25 μm, wherein the coating layer is a double-layer comprised of a 25 to 300 nm inner layer of gold and an adjacent 0.5 to 25 nm thick outer layer of palladium.

5. A process for the manufacture of a coated wire according to claim 1, the process comprising: (1) providing a precursor item consisting of (a) pure silver consisting of (a1) silver in an amount in the range of from 99.99 to 100 wt.-% and (a2) further components in a total amount of from 0 to 100 wt.-ppm or (b) doped silver consisting of (b1) silver in an amount in the range of from >99.49 to 99.997 wt.-%, (b2) at least one doping element selected from the group consisting of calcium, nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount of from 30 to <5000 wt.-ppm and (b3) further components in a total amount of from 0 to 100 wt.-ppm, or (c) a silver alloy consisting of (c1) silver in an amount in the range of from 89.99 to 99.5 wt.-%, (c2) at least one alloying element selected from the group consisting of nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount in the range of from 0.5 to 10 wt.-% and (c3) further components in a total amount of from 0 to 100 wt.-ppm, or (d) a doped silver alloy consisting of (d1) silver in an amount in the range of from >89.49 to 99.497 wt.-%, (d2) at least one doping element selected from the group consisting of calcium, nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount of from 30 to <5000 wt.-ppm, (d3) at least one alloying element selected from the group consisting of nickel, platinum, palladium, gold, copper, rhodium and ruthenium in a total amount in the range of from 0.5 to 10 wt.-% and (d4) further components in a total amount of from 0 to 100 wt.-ppm, wherein the at least one doping element (d2) is other than the at least one alloying element (d3), wherein the individual amount of any further component is less than 30 wt.-ppm, wherein the individual amount of any doping element is at least 30 wt.-ppm, and wherein all amounts in wt.-% and wt.-ppm are based on the total weight of the precursor item, (2) elongating the precursor item to form an elongated precursor item, until an intermediate cross-section in the range of from 706 to 31400 μm.sup.2 or an intermediate diameter in the range of from 30 to 200 μm is obtained, (3) depositing a double-layer coating of an inner layer of palladium and an adjacent outer layer of gold or an inner layer of gold and an adjacent outer layer of palladium on the surface of the elongated precursor item obtained after completion of process step (2), (4) further elongating the coated precursor item obtained after completion of process step (3) until a desired final cross-section or diameter is obtained, and (5) finally strand annealing the coated precursor obtained after completion of process step (4) at an oven set temperature in the range of from 150 to 600° C. for an exposure time in the range of from 0.4 to 0.8 seconds to form the coated wire, wherein step (2) may include one or more sub-steps of intermediate batch annealing of the precursor item at an oven set temperature of from 400 to 800° C. for an exposure time in the range of from 50 to 150 minutes.

6. The process of claim 5, wherein the final strand annealing is performed at an oven set temperature in the range of from 200 to 400° C.

7. The process of claim 5, wherein the finally strand annealed coated precursor is quenched in water which may contain one or more additives.

8. The process of claim 5, wherein the optional intermediate batch annealing of process step (2) is performed in an inert or reducing atmosphere.

9. A coated wire obtainable by a process according to claim 5.

Description

EXAMPLES

Preparation of FAB:

[0034] It was worked according to the procedures described in the KNS Process User Guide for FAB (Kulicke & Soffa Industries Inc, Fort Washington, Pa., USA, 2002, 31 May 2009) in ambient atmosphere. FAB was prepared by performing conventional electric flame-off (EFO) firing by standard firing (single step, 17.5 μm wire, EFO current of 50 mA, EFO time 125 μs).

Test methods A. to C.

[0035] All tests and measurements were conducted at T=20° C. and a relative humidity RH=50%.

A. Salt-Solution Soaking Test of Bonded Balls:

[0036] The wires were ball bonded to Al-0.5 wt.-% Cu bond pads. The test devices with the so-bonded wires were soaked in salt-solution at 25° C. for 10 minutes, washed with deionized (DI) water and later with acetone. The salt-solution contained 20 wt.-ppm NaCl in DI water. The number of lifted balls were examined under a low power microscope (Nikon MM-40) at 100× magnification. Observation of a higher number of lifted balls indicated severe interfacial galvanic corrosion.

B. FAB Morphology

[0037] The formed FAB was examined by scanning electron microscope (SEM) with a magnification of 1000.

Evaluation:

[0038] ++, very good (round ball)
+, good (round ball);
0, acceptable (not perfectly round, but no obvious plateau on the FAB surface);
−, peach ball (two plateaus with distinct hemisphere at FAB tip)
−−, severe peach ball (two plateaus with distinct hemisphere at FAB tip)
C. Off center ball (OCB) occurrence

[0039] The formed FAB descended to a Al—0.5 wt.-% Cu bond pad from a predefined height (tip of 203.2 μm) and speed (contact velocity of 6.4 μm/sec). Upon touching the bond pad, a set of defined bonding parameters (bond force of 100 g, ultrasonic energy of 95 mA and bond time of 15 ms) took into effect to deform the FAB and formed the bonded ball. After forming the ball, the capillary rose to a predefined height (kink height of 152.4 μm and loop height of 254 μm) to form the loop. After forming the loop, the capillary descended to the lead to form the stitch. After forming the stitch, the capillary rose and the wire clamp closed to cut the wire to make the predefined tail length (tail length extension of 254 μm). For each sample five bonded wires were optically inspected using a microscope with a magnification of 1000.

Evaluation:

[0040] ++, perfect centered
+, centered;
0, acceptably off-centered;
−, off-centered;
−−, very off-centered.

Wire Examples 1 to 18

[0041] A quantity of silver (Ag) and, optionally, palladium (Pd) of at least 99.99% purity (“4N”) in each case were melted in a crucible. In some cases small amounts of silver-nickel or silver-platinum master alloys were added to the melt and uniform distribution of the added components was ascertained by stirring. The following master alloys were used:

TABLE-US-00001 Master Alloy Composition Ag-0.5 wt.-% Ni 99.5 wt.-% Ag 0.5 wt.-% Ni Ag-0.5 wt.-% Pt 99.5 wt.-% Ag 0.5 wt.-% Pt

[0042] For the wire core alloys of Table 1 a corresponding combination of master alloys were added.

[0043] Then a wire core precursor item in the form of 8 mm rods was continuous cast from the melt. The rods were then drawn in several drawing steps to form a wire core precursor having a circular cross-section with a diameter of 134 μm. The wire core precursor was intermediate batch annealed at an oven set temperature of 500° C. for an exposure time of 60 minutes and thereafter further drawn to a final diameter of 17.5 μm, followed by a final strand annealing at an oven set temperature of 220° C. for an exposure time of 0.6 seconds, immediately followed by quenching the so-obtained coated wires in water containing 0.07 vol.-% of surfactant.

[0044] In case of reference wires 4 to 6 the wire core precursor was electroplated with a coating layer consisting of gold of at least 99% purity and thereafter further drawn to a final diameter of 17.5 μm and a final gold coating layer thickness of 250 nm, followed by a final strand annealing at an oven set temperature of 220° C. for an exposure time of 0.6 seconds, immediately followed by quenching the so-obtained coated wires in water containing 0.07 vol.-% of surfactant.

[0045] For the inventive wires 1 to 12, a double layer comprising gold and palladium was electroplated instead of a single gold layer as described above (final palladium layer thickness=5 nm, final gold layer thickness=250 nm). In some embodiments the palladium layer was plated first followed by an outer layer of gold, in other embodiments the gold layer was plated first followed by an outer layer of palladium.

[0046] By means of these procedures, several different samples 1 to 12 of double-coated silver or silver-based wires and uncoated and single-layer gold coated reference silver wires (Ref) were manufactured. Table 1 shows the composition of the wires.

TABLE-US-00002 TABLE 1 wire core alloying/doping Coating elements inner coating outer coating wt.-% wt.-ppm Sample layer [nm] [nm] Pd Ni Pt 4N Ag (Ref 1) none None 0.0002 2 2 doped Ag (Ref 2) none None 0.4 2 2 Alloyed Ag none None 1.5 2 2 (Ref 3) 4N Ag (Ref 4) none gold [250 nm] 0.0002 2 2 doped Ag (Ref 5) none gold [250 nml 0.4 2 2 Alloyed Ag none gold [250 nm] 1.5 2 2 (Ref 6)  1 (invention) gold [250 nm] palladium [5 nm] 0.0002 2 2  2 (invention) gold [250 nm] palladium [5 nm] 0.4 2 2  3 (invention) gold [250 nm] palladium [5 nm] 1.5 2 2  4 (invention) gold [250 nm] palladium [5 nm] 0.0002 2 500  5 (invention) gold [250 nm] palladium [5 nm] 0.4 40 2  6 (invention) gold [250 nm] palladium [5 nm] 1.5 40 2  7 (invention) palladium [5 nm] gold [250 nm] 0.0002 2 2  8 (invention) palladium [5 nm] gold [250 nm] 0.4 2 2  9 (invention) palladium [5 nm] gold [250 nm] 1.5 2 2 10 (invention) palladium [5 nm] gold [250 nm] 0.0002 2 500 11 (invention) palladium [5 nm] gold [250 nm] 0.4 40 2 12 (invention) palladium [5 nm] gold [250 nm] 1.5 40 2

[0047] Table 2 below shows certain test results. All tests were carried out with wires of 17.5 μm diameter

TABLE-US-00003 TABLE 2 Ref Ref Ref Ref Ref Ref 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 10 11 12 Salt-solution 85 78 73 7 5 8 5 5 2 4 3 2 6 3 4 2 1 3 soaking test of bonded balls FAB morphology −− −− − 0 0 0 + + ++ + + ++ + ++ + ++ ++ ++ OCB occurrence −− −− −− − − 0 + + ++ + + ++ ++ ++ ++ ++ ++ ++