Sintering paste

Abstract

A sintering powder comprising: a particulate having a mean longest diameter of less than 10 microns, wherein at least some of the particles forming the particulate comprise a metal at least partially coated with a capping agent. A sintering paste and sintering film comprising the sintering powder. A method for making a sintered joint by sintering the sintering powder, paste, or film in the vicinity of two or more workpieces.

Claims

1. A sintering paste comprising: a sintering powder, wherein the sintering powder comprises, a particulate comprising particles having a mean longest diameter of less than 10 microns, wherein at least some of the particles forming the particulate comprise a metal at least partially coated with a capping agent, wherein the particulate comprises a first type of particles having a longest diameter of from 1 to 100 nm and a second type of particles having a longest diameter of from greater than 100 nm to 50 microns, wherein the particulate comprises from 81 to 99 wt % of the first type of particles and from 1 to 19 wt % of the second type of particles; an organosilver compound in a concentration of 1-25 wt %; and a solvent.

2. The sintering paste of claim 1, wherein the organosilver compound comprises one or more of silver oxalate, silver lactate, silver succinate, silver neodecanoate, silver citrate and silver stearate.

3. The sintering paste of claim 1, further comprising a fatty acid.

4. The sintering paste of claim 1, further comprising a peroxide.

5. The sintering paste of claim 1, wherein the paste is resin free.

6. The sintering paste of claim 1, wherein the paste is pin transferable and/or exhibits a thermal conductivity of greater than 200 W/mK and/or is capable of providing a die shear strength of from 25 to 45 MPa.

7. The sintering paste of claim 1, wherein the sintering paste is applied in a sintering film.

8. The sintering paste of claim 1, further comprising at least one of an activator, a rheology modifier, and a surfactant.

9. The sintering paste of claim 1, wherein the first type of particles and the second type of particles are at least partially coated with the same capping agent.

10. The sintering paste of claim 1, wherein the particulate of particles comprises 0.1 to 3 wt % capping agent.

11. The sintering paste of claim 10, wherein the second type of particles does not contain capping agent.

12. The sintering paste of claim 10, wherein the capping agent is octylamine.

13. The sintering paste of claim 1 comprising 2-10 wt % of the organosilver compound.

14. The sintering paste of claim 1, further comprising a binder.

15. The sintering paste of claim 14, wherein the binder comprises an epoxy-based resin.

16. The sintering paste of claim 1, wherein the solvent comprises at least one of a monoterpene alcohol, a glycol, and glycol ether.

17. The sintering paste of claim 1 comprising at least one of: i. from 1 to 15 wt % binder; ii. from 1 to 15 wt % solvent; iii. up to 1 wt % rheology modifier; iv. up to 1 wt % activator; and v. up to 6 wt % surfactant.

18. The sintering paste of claim 1, wherein the organosilver compound comprises silver oxalate.

19. The sintering paste of claim 1, wherein the organosilver compound comprises silver lactate.

20. The sintering paste of claim 13, wherein the organosilver compound comprises silver oxalate.

Description

(1) The invention will now be described in relation to the following non-limiting Figures, in which:

(2) FIG. 1 shows TEM micrographs of a sintering powder of the present invention.

(3) FIG. 2 shows histograms of the particles sizes of a sintering powder of the present invention.

(4) FIG. 3 shows a powder X-ray diffraction pattern of a sintering powder of the present invention.

(5) FIG. 4 shows a thermogram of a sintering powder of the present invention.

(6) FIG. 5 shows the results of differential scanning calorimetry (DSC) analysis of a sintering powder of the present invention.

(7) FIG. 6 shows the topology of a printed sintering paste of the present invention. The paste has a height of from 80 to 90 μm. There are no flat deposits, no dog-ears and no undulations.

(8) FIG. 7 shows cross-sections of a joint formed between a Si die and a substrate using a sintering paste of the present invention. The images indicate good adhesion of the sintered paste to the metallization of the die as well as the substrate.

(9) FIG. 8 shows a wet and a free standing dry film of the present invention together with the morphology of the film.

(10) FIG. 9 shows Keyance microscope images of the topology of dispensed paste according to the present invention: dots (left hand side), pattern (right hand side).

(11) FIG. 10 shows Koh Young images of dispensed paste according to the present invention: typical image of dispensed dots (left hand side), volume measurement (right hand side).

(12) The invention will now be described in relation to the following non-limiting examples.

EXAMPLE 1—PREPARATION OF SINTERING POWDER

(13) The sintering powder was prepared in a single phase reaction. A 3 M ethylene glycol solution of silver nitrate was prepared by adding silver nitrate to ethylene glycol and stirring at 0 to 5° C. until the solution became clear. The solution was then made to 0.3 M by adding a mixture of 50% toluene and 50% ethanol. The silver nitrate solution (0.3 M, 3.5 liter) was then added to a toluene solution of octylamine (3.5 kg, 27.07 moles), which was prepared by adding octylamine to toluene at room temperature. 262.5 g (0.998 M, 5.24 moles) of 80% hydrazine hydrate dissolved in N,N dimethyl formamide was then immediately added. The reaction mixture was stirred for 45 minutes at a speed of 350 rpm before being allowed to settle for few a minutes. The colorless supernatant solution was then pumped out and the silver nanoparticles, which had settled at the bottom of the tank, were transferred to a Buchner funnel and washed with methanol to remove excess octylamine. Finally, the powder was washed with acetone and dried under vacuum at room temperature. The yield of the reaction was around 98%.

(14) TEM micrographs of the powder were obtained and are shown in FIG. 1. The micrographs indicate silver nanoparticles heterogeneous in size ranging from 5 to 60 nm. Furthermore, the micrographs appear to indicate the distribution of very small particles around the larger grains. The distribution of the particles sizes is shown in FIG. 2 and appears to be bimodal.

(15) FIG. 3 shows the powder X-ray diffraction pattern of the powder and indicates a face-centred cubic structure. Using the Scherrer formula, the mean particle size was calculated to be around 25 nm. This particle size was confirmed by the use of a particle size analyser (Microtrac Nanotrac Ultra NPA 253) which indicated a D50 of around 20 nm.

(16) The powder was subjected to thermogravimetric analysis (TGA) and the corresponding thermogram is shown in FIG. 4. The results indicate that the powder comprises approximately 1 wt % capping agent, i.e. octylamine.

(17) The sintering temperature of the powder was analysed using differential scanning calorimetry (DSC) and the results are shown in FIG. 5. The plot indicates a sintering temperature of 195.2° C. with a specific heat of 36.7 J/g.

EXAMPLE 2—PREPARATION OF SINTERING PASTE

(18) 3 g of epoxy resin was added to 40 g of the powder of Example 1. It was then mixed in an orbital mixer at 1000 rpm. To the mixture, 3 g of solvent mixture (1.5 g of terpineol and 1.5 g of triethylene glycol) was added and mixed in an orbital mixer at 1000 rpm. After mixing it was milled in a three roll mill for a few minutes to provide a homogeneous paste. The composition of the paste is shown in Table 1.

(19) TABLE-US-00001 TABLE 1 Composition of the paste Component Weight % Silver 86.96 Resin 6.52 Solvent mixture 6.52

(20) The tackiness, viscosity and thermal conductivity of the paste were measured and the results are shown in Table 2. The tackiness was measured in a Rhesca tackiness tester tac (II) using Japanese Industrial Standard (JIS). The paste was printed on a microscopic glass side using a 10 mil stencil of three circular openings. The immersion speed of the probe was 120 mm/min and a test speed of 600 mm/min was used with a press time of 0.2 seconds. The viscosity of the paste was measured using a Brookfield DVIII ultra programmable rheometer (Spindle CP51). The thermal conductivity was measured using a Netzsch LFA 447 Nanoflash. Thermal conductivity K was calculated using the following formula:
K=αρcp
where α is the thermal diffusivity (m.sup.2/s), ρ is the density of the material (kg/m.sup.3) and cp is the specific heat capacity (J/kg-K). The tackiness, viscosity and thermal conductivity values for Examples 3, 4, 12 and 26 were measured in a similar manner.

(21) TABLE-US-00002 TABLE 2 Properties of the paste Tackiness (JIS) 105-125 gf Viscosity (2 rpm) 170 (±15) (Pa-s) Thermal 80 W/m K conductivity

EXAMPLE 3

(22) 4 g of epoxy resin was added to 40 g of the powder of Example 1. It was then mixed in an orbital mixer at 1000 rpm. 4 g of terpineol was then added and mixing in the orbital mixer at 1000 rpm was continued. After mixing the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(23) TABLE-US-00003 TABLE 3 Composition of the paste Component Weight % Silver 83.34 Resin 8.33 Terpineol 8.33

(24) TABLE-US-00004 TABLE 4 Properties of the paste Tackiness (JIS) 120-140 gf Viscosity (5 rpm) 40 (±10) (Pa-s)

EXAMPLE 4

(25) 8 g of epoxy resin and 6.67 g of terpineol were mixed thoroughly so as to obtain a homogeneous solution, which was then added to 40 g of powder of Example 1. It was then mixed in an orbital mixer at 1000 rpm. To the mixture, 4 g of terpineol was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for few minutes to obtain a homogenous paste.

(26) TABLE-US-00005 TABLE 5 Composition of the paste Component Weight % Silver 73.17 Resin 14.63 Terpineol 12.20

(27) TABLE-US-00006 TABLE 6 Properties of the paste Tackiness (JIS) 170-220 gf Viscosity (5 rpm) 30 (±10) (Pa-s)

EXAMPLE 5

(28) 2.5 g of epoxy resin, 3.4 g of solvent mixture (1.7 g of terpineol and 1.7 g of triethylene glycol) and 0.1 g of cryvallac super were mixed thoroughly to obtain a homogeneous solution, which was then added to 40 g of powder of Example 1. It was then mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(29) TABLE-US-00007 TABLE 7 Composition of the paste Component Weight % Silver 86.96 Resin 5.43 Solvent 7.4 mixture Rheology 0.21 modifier

EXAMPLE 6

(30) 2.7 g of epoxy resin, 3 g of solvent mixture (1.5 g of terpineol and 1.5 g of triethylene glycol) and 0.3 g of succinic acid were mixed thoroughly to obtain a homogeneous solution, which was then added to 40 g of powder of Example 1. It was then mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(31) TABLE-US-00008 TABLE 8 Composition of the paste Component Weight % Silver 86.96 Resin 5.86 Solvent 6.52 mixture Activator 0.66

EXAMPLE 7

(32) 2.6 g of epoxy resin, 3 g of solvent mixture (1.5 g of terpineol and 1.5 g of triethylene glycol), 0.3 g of succinic acid and 0.1 g of cryvallac super were mixed thoroughly and added to 40 g of powder of Example 1. Mixing was then carried out in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(33) TABLE-US-00009 TABLE 9 Composition of the paste Component Weight % Silver 86.96 Resin 5.65 Solvent 6.52 mixture Rheology 0.21 modifier Activator 0.66

EXAMPLE 8

(34) 40 g of the powder of Example 1, 2.88 g of epoxy resin and 0.25 g of Disperbyk163 were mixed in orbital mixer at 1000 rpm. 2.88 g of solvent mixture (propylene glycol, methyl digol and terpineol) was then added. After mixing, the mixture was milled in a three roll mill for few minutes to obtain a homogenous paste.

(35) TABLE-US-00010 TABLE 10 Composition of paste Composition Weight % Silver 86.94 Resin 6.26 Disperbyk163 0.54 Propylene glycol 1.565 Methyl digol 1.565 Terpineol 3.13

EXAMPLE 9

(36) 40 g of the powder of Example 1, 2.88 g of epoxy resin and 0.25 g of TritonX 100 were mixed in orbital mixer at 1000 rpm. 2.88 g of solvent mixture (propylene glycol, methyl digol and terpineol) was then added. After mixing, the mixture was milled in a three roll mill for few minutes to obtain a homogenous paste.

(37) TABLE-US-00011 TABLE 11 Composition of paste Composition Weight % Silver 86.94 Resin 6.26 TritonX100 0.54 Propylene glycol 1.565 Methyl digol 1.565 Terpineol 3.13

EXAMPLE 10

(38) 40 g of the powder of Example 1, 2.88 g of epoxy resin and 0.25 g of Disperbyk163 were mixed in orbital mixer at 1000 rpm. 2.88 g of solvent mixture was then added. After mixing, the mixture was milled in a three roll mill for few minutes to obtain a homogenous paste.

(39) TABLE-US-00012 TABLE 12 Composition of paste Composition Weight % Silver 86.94 Resin 6.26 Disperbyk 163 0.54 Glycolic ester 3.13 Terpineol 3.13

EXAMPLE 11

(40) 40 g of the powder of Example 1, 2.93 g of epoxy resin, 0.25 g of Disperbyk163 and 0.125 g of hydoxypropylmethylcellulose were mixed in orbital mixer at 1000 rpm. 3.7 g of solvent mixture (terpineol and triacetin) was then added. After mixing, the mixture was milled in a three roll mill for few minutes to obtain a homogenous paste.

(41) TABLE-US-00013 TABLE 13 Composition of paste Composition Weight % Silver 85.1 Resin 6.22 Disperbyk 163 0.53 Hydoxypropylmethylcellulose 0.27 Triacetin(Plastiziser) 3.94 Terpineol 3.94

EXAMPLE 12

(42) 40 g of the powder of Example 1, 2.35 g of epoxy resin, 0.46 g of Disperbyk163 and 0.46 g of polyvinyl acetate were mixed in orbital mixer at 1000 rpm. 3.72 g of solvent mixture (propylene glycol, methyl digol and terpineol) was then added. After mixing, the mixture was milled in a three roll mill for few minutes to obtain a homogenous paste.

(43) TABLE-US-00014 TABLE 14 Composition of paste Composition Weight % Silver 85.1 Resin 5.0 Disperbyk 163 1.0 Polyvinyl 1.0 acetate Propylene 1.97 glycol Methyl digol 1.97 Terpineol 3.96

(44) The properties of the paste are set out in Table 14.

(45) TABLE-US-00015 TABLE 15 Properties of paste (volume resistivity measured using four probe method) Specific Heat 0.413 J/g/K Thermal 48.1 mm.sup.2/s diffusivity Thermal 88.7 W/m/K conductivity Volume 2.8 × 10.sup.−5 Ω cm resistivity

(46) The tackiness and viscosity of the paste were measured at regular intervals to observe the stability of the paste, and the results are set out in Table 15. The results indicate that the paste is stable for 25 days at room temperature and pressure.

(47) TABLE-US-00016 TABLE 16 Viscosity/tackiness over time Viscosity (PAS) at Days 2 rpm Tackiness (g/f) 1 164 140 10 168 149 25 170 151

EXAMPLE 13

(48) 6 g of epoxy resin was added to 30 g of the powder of Example 1. 5 g of terpineol was then added. The mixture was then mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(49) TABLE-US-00017 TABLE 17 Composition of paste Composition Weight % Silver 73.17 powder Resin 14.63 Terpineol 12.20

EXAMPLE 14

(50) 4.9 g of epoxy resin was added to 30 g of the powder of Example 1. 2 g of terpineol and 2 g of triethylene glycol was then added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(51) TABLE-US-00018 TABLE 18 Composition of paste Composition Weight % Silver 77.12 powder Resin 12.60 Terpineol 5.14 Triethylene 5.14 glycol

EXAMPLE 15

(52) 6 g of epoxy resin was added to 30 g of the powder of Example 1. 3 g of terpineol and 3 g of triethylene glycol was then added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(53) TABLE-US-00019 TABLE 19 Composition of paste Composition Weight % Silver 71.44% powder Resin 14.28% Terpineol 7.14% Triethylene 7.14% glycol

EXAMPLE 16—PRINTING PASTE

(54) The paste of Example 8 was printed on direct bond copper (DBC) having Au/Ni finish with a 3 mil stencil having an aperture size of 7 mm*7 mm. The printed surface was observed to be absolutely flat having no undulation. The thickness of the printed layer was around 75 μm.

(55) The printed layer was sintered in a box oven by heating the film at 160° C. for 90 minutes. SEM indicated the necking of the silver nanoparticle with a good packing fraction.

EXAMPLE 17—PREPARATION OF FILM

(56) The paste of Example 2 was printed on a silicon coated polyester sheet. It was then heated at 130° C. for 30 minutes in a hot plate/box oven. The resulting film was de-attached from the sheet and could be used as a free standing film. FIG. 8 shows the film as printed in wet condition and also as a free standing dry film after being de-attached from the polyester sheet. No cracks were found in the film after it was de-attached from the polyester sheet. The thickness of the dried film was 72 μm.

(57) The silver film was then placed on silicon rubber. The die of 3 mm*3 mm was stamped onto the film by putting a pressure of 2 MPa for a second at 130° C. with help of die bonder.

EXAMPLE 18—DISPENSING PASTE

(58) The paste of Example 15 was dispensed using a Nordson Auger Valve. The following were the set parameters for dispensing: Needle size: 22 Gauge Pressure: 1 Bar Dispense Type: Point and pattern Dispense Time: 0.15 sec

(59) The topology of the dispensed pattern was examined using a Keyance microscope (see FIG. 9). It was seen that the all the dispensed dots and patterns were of the same diameter (˜520 microns) and length (2.3 mm), respectively. The volume of the dispensed patterns were then examined using a Koh Young apparatus (see FIG. 10), which revealed consistent dispense deposit and height (˜63.6 microns to 67.2 microns).

EXAMPLE 19

(60) 5.55 g of terpineol was mixed with 1.48 g of Silver Oxalate. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(61) TABLE-US-00020 TABLE 20 Composition of paste Composition Weight % Silver 81% powder Silver  4% oxalate Terpineol 15%

EXAMPLE 20

(62) 1.39 g of terpineol, 2.08 g of propylene glycol, 2.08 g of methyl digol was mixed with 1.48 g of Silver Oxalate. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(63) TABLE-US-00021 TABLE 21 Composition of paste Composition Weight % Silver powder   81% Silver oxalate   4% Propylene glycol 5.61% Methyl digol 5.61% Terpineol 3.78%

EXAMPLE 21

(64) 0.925 g of terpineol, 1.39 g of propylene glycol, 1.39 g of methyl digol was mixed with 3.33 g of Silver Oxalate. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(65) TABLE-US-00022 TABLE 22 Composition of paste Composition Weight % Silver powder   81% Silver oxalate   9% Propylene glycol 3.75% Methyl digol 3.75% Terpineol  2.5%

EXAMPLE 22

(66) 0.9 g of terpineol, 1.35 g of propylene glycol, 1.35 g of methyl digol was mixed with 7.2 g of Silver Oxalate. To this mixture 25.2 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(67) TABLE-US-00023 TABLE 23 Composition of paste Composition Weight % Silver powder   70% Silver oxalate   20% Propylene glycol 3.75% Methyl digol 3.75% Terpineol  2.5%

EXAMPLE 23

(68) 0.074 g of Lauric acid was mixed with 2.59 g of Silver Oxalate. To this 1.85 g of terpineol, 2.22 g of propylene carbonate, 0.296 g of Hydrogen peroxide was added and mixed. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(69) TABLE-US-00024 TABLE 24 Composition of paste Composition Weight % Silver powder  81% Silver oxalate   7% Lauric Acid 0.2% Propylene carbonate 6.00%  Terpineol 5.00%  Hydrogen peroxide 0.8%

EXAMPLE 24

(70) 0.074 g of Lauric acid was mixed with 3.33 g of Silver Oxalate. To this 1.85 g of terpineol, 1.48 g of propylene carbonate, 0.296 g of hydrogen peroxide was added and mixed. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(71) TABLE-US-00025 TABLE 25 Composition of paste Composition Weight % Silver powder   81% Silver oxalate   9% Lauric Acid  0.2% Propylene carbonate 4.00% Terpineol 5.00% Hydrogen peroxide  0.8%

EXAMPLE 25

(72) 0.074 g of Lauric acid was mixed with 2.96 g of Silver Oxalate. To this 2.03 g of terpineol, 1.67 g of propylene carbonate, 0.296 g of hydrogen peroxide was added and mixed. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(73) TABLE-US-00026 TABLE 26 Composition of paste Composition Weight % Silver powder  81% Silver oxalate   8% Lauric Acid 0.2% Propylene carbonate 4.5% Terpineol 5.48%  Hydrogen peroxide 0.8%

EXAMPLE 26

(74) 0.074 g of Lauric acid was mixed with 2.96 g of Silver Oxalate. To this 2.58 g of terpineol, 1.11 g of propylene carbonate, 0.296 g of hydrogen peroxide was added and mixed. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(75) TABLE-US-00027 TABLE 27 Composition of paste Composition Weight % Silver powder  81% Silver oxalate   8% Lauric Acid 0.2% Propylene carbonate 3.0% Terpineol 6.98%  Hydrogen peroxide 0.8%

(76) The properties of the paste are set out in the table below.

(77) TABLE-US-00028 TABLE 28 Properties of paste Specific Heat 0.27 J/g .Math. K Thermal 99.5 mm.sup.2/s diffusivity Thermal 223.6 W/m .Math. K conductivity Density 8.65 g/cm.sup.3 Viscosity at 50 (±10%) 2 rpm (Pas) Tack (gf) 95 (±10%)

(78) The paste of this example exhibits good printing features. The cross section of a die attached material using the paste exhibited an excellent packing fraction, and the joint strength was around 20 MPa.

EXAMPLE 27

(79) 0.212 g of Lauric acid was mixed with 3.59 g of Silver Oxalate. To this 5.89 g of terpineol, 4.85 g of propylene carbonate, 0.859 g of hydrogen peroxide was added and mixed. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(80) TABLE-US-00029 TABLE 29 Composition of paste Composition Weight % Silver powder 69.99% Silver oxalate  6.99% Lauric Acid 0.413% Propylene carbonate  9.45% Terpineol 11.48% Hydrogen peroxide 1.674%

EXAMPLE 28

(81) 0.174 g of Lauric acid was mixed with 4.61 g of Silver Oxalate. To this 4.86 g of terpineol, 4 g of propylene carbonate, 0.708 g of hydrogen peroxide was added and mixed. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(82) TABLE-US-00030 TABLE 30 Composition of paste Composition Weight % Silver powder 72.01%  Silver oxalate 9.00% Lauric Acid 0.34% Propylene carbonate  7.8% Terpineol 9.47% Hydrogen peroxide 1.38%

EXAMPLE 29

(83) 0.074 g of Lauric acid was mixed with 2.96 g of Silver Lactate. To this 2.58 g of terpineol, 1.11 g of propylene carbonate, 0.296 of Hydrogen peroxide was added and mixed. To this mixture 30 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(84) TABLE-US-00031 TABLE 31 Composition of paste Composition Weight % Silver powder  81% Silver Lactate   8% Lauric Acid 0.2% Propylene carbonate 3.0% Terpineol 6.98%  Hydrogen peroxide 0.8%

EXAMPLE 30

(85) 0.074 g of Lauric acid was mixed with 7.4 g of Silver Lactate. To this 2.59 g of terpineol, 1.11 g of propylene carbonate, 0.296 of Hydrogen peroxide was added and mixed. To this mixture 25.55 g of the powder of Example 1 was added and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

(86) TABLE-US-00032 TABLE 32 Composition of paste Composition Weight % Silver powder  69% Silver Lactate  20% Lauric Acid 0.2% Propylene carbonate 3.0% Terpineol 7.0% Hydrogen peroxide 0.8%

EXAMPLE 31

(87) 85-90% of the powder of Example 1 and 0 to 1% of fatty acid was mixed in a jar A. In another jar B, 0 to 3% of propylene carbonate, 3 to 8% of terpineol, 3 to 8% triethylene glycol and 0 to 2% organic peroxide were mixed. The mixture from jar A was added to jar B and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

EXAMPLE 32

(88) 80-85% of the powder of Example 1, 0 to 5% of silver compound and 0 to 1% of fatty acid was mixed in a jar A. In another jar B, 0 to 3% of propylene carbonate, 3 to 8% of terpineol, 7 to 10% triethylene glycol and 0 to 2% organic peroxide were mixed. The mixture from jar A was added to jar B and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

EXAMPLE 33

(89) 85-90% of the power of Example 1, 0 to 5% of silver compound and 0 to 1% of fatty acid was mixed in a jar A. In another jar B, 0 to 3% of propylene carbonate, 3 to 8% of terpineol, 3 to 8% triethylene glycol and 0 to 2% organic peroxide were mixed. The mixture from jar A was added to jar B and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

EXAMPLE 34

(90) 75-80% of the powder of Example 1, 0 to 5% of silver compound and 0 to 1% of fatty acid was mixed in a jar A. In another jar B, 0 to 3% of propylene carbonate, 3 to 8% of terpineol, 6 to 12% triethylene glycol and 0 to 5% organic peroxide were mixed in jar B. The mixture from jar A was added to jar B and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

EXAMPLE 34

(91) 80-85% of the powder of Example 1, 5 to 10% of Silver compound and 0 to 1% of fatty acid was mixed in a jar A. In another jar B, 0 to 5% of propylene carbonate, 0 to 5% of terpineol, 3 to 7% triethylene glycol and 0 to 2% organic peroxide were mixed. The mixture from jar A was added to jar B and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste

EXAMPLE 35

(92) 0.3M AgNO.sub.3 solution was made in aqueous medium. To the aqueous solution of AgNO.sub.3, reducing agent was added drop wise. The solution was stirred for 1 hour at room temperature. Silver starts precipitating out on the addition of the reducing agent and the supernatant becomes fully colorless. The solution mixture was then filtered using a Buchner funnel. The micron silver powder obtained was then washed with water so as to remove excess silver salt and reducing agent. Final washing was then done with acetone so as to ensure the complete removal of water.

(93) The powder obtained was then characterized with SEM, indicating a particle size of around 600 nm to 1 micron.

EXAMPLE 36

(94) 80-85% of mixture the powders of Example 1 and Example 35 (about 90 wt % Example 1, about 10 wt % Example 35), 5 to 10% of silver lactate and 0 to 1% of lauric acid were mixed in a jar A. In another jar B, 0 to 5% of propylene carbonate, 0 to 5% of terpineol, 3 to 7% triethylene glycol and 0 to 2% organic peroxide were mixed. The mixture from jar A was added to jar B and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste

EXAMPLE 37

(95) 85-90% of the powder of Example 35, 0 to 5% of silver lactate and 0 to 1% of lauric acid were mixed in a jar A. In another jar 0 to 3% of propylene carbonate, 3 to 8% of terpineol, 3 to 8% triethylene glycol and 0 to 2% organic peroxide were mixed in jar B. The mixture from Jar A was added to B and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste.

EXAMPLE 38

(96) 80-85% of the powder of Example 35, 5 to 10% of silver lactate and 0 to 1% of lauric acid was mixed in a jar A. In another jar 0 to 5% of propylene carbonate, 0 to 5% of terpineol, 3 to 7% triethylene glycol and 0 to 2% organic peroxide were mixed in jar B. The mixture from Jar A was added to B and mixed in an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes to obtain a homogenous paste

EXAMPLE 39—PRINTING PASTE

(97) Print Definition:

(98) The paste of Example 31 was printed on direct bond copper (DBC) having Au/Ni finish with a 3 mil stencil having an aperture size of 3 mm*3 mm. It was observed that the printed surface was absolutely flat having no undulation. The thickness of the printed layer was around 75 um.

(99) Die Placement:

(100) Gold metalized silicon dies were placed on the printed pattern using a die bonder. The uniform print deposit was confirmed by Koh Young 8030 as shown in graph below. The vehicle was then kept in a box oven for sintering at different temperature profile.

(101) Temperature Profile:

(102) Silicon die metallized with gold coating was placed with the help of a die bonder using controlled Z height and was sintered at 180° C., 200° C., 225° C. and 250° C. in a box oven. It is seen that the joint strength decreased when heated after 225° C.

(103) In this Example, 200° C. was considered the optimized sintering temperature, since high temperature die shear at 260° C. shows a drop of around 50%.

(104) Cross Section of the Sintered Layer:

(105) The cross section of the above die attached material shows a good diffusion of silver nanoparticle at both the interfaces (die side as well as on the substrate side). SEM reveals a very good packing fraction with very good necking phenomena.

(106) Dispense Topology:

(107) The paste of the above example was also dispensed using Nordson EFD dispenser. The nanosilver paste was dispensed at 0.8 bar pressure and a speed of 40 mm/sec on lead frames.

(108) Die Placement:

(109) Gold metalized silicon dies were placed on the dispensed pattern using a die bonder. Uniform dispensing was observed throughout. The vehicle was kept in a box oven. The average die shear obtained was around 20-25 MPa with 100% pad coverage. About 20% deterioration was seen when the shearing was done at 260° C.

(110) Cross Section of the Sintered Layer:

(111) The cross section of the above die attached material shows a good diffusion of silver nanoparticle at both the interfaces (die side as well as on the substrate side). SEM reveals the bond line thickness of around 20 micron.

(112) As will be appreciated, the method, powder, paste and film disclosed herein are associated with a number of benefits over prior art techniques. In particular, there is no slump phenomena, no bridges, no bubbles in print deposit, no bleed-out and no aperture blocking when printing with the paste. Moreover, it is possible to provide a paste height of from 80-90 micrometers with flat deposits, no Dog—ears and no undulations. Thus, the benefits of the paste which includes a binder (e.g. resin) include: Pressure-less Sintering Process ability in standard SMT Line Flat and uniform surface topology Die Shear Strength average >20 MPa No interfacial failure mode Room Temp Stability=min 1 month Thermal Cycling: Acceptable joint strength up to 1500 cycles (−40 C to +125 C, 10 min dwell). Needle and Jet Dispensable Film Form Factor

(113) In addition to the benefits mentioned above, the paste containing organosilver compound has some further benefits which are listed below: High die shear strength (25 to 45 MPa) High thermal conductivity (>200 W/mK) Pin transferable Good high thermal properties

(114) The sintering powder, paste and film will now be further described, by way of example, with reference to the following non-limiting applications A-H:

(115) A. Attachment of semiconductor die (either flip chip or wire bonded), onto a variety of substrates such as DBC (Direct Bond Copper), DPC (Direct Plate Copper), MCPCB (Metal Core PCBs), FR4, Copper lead-frames, Flexible PCBs and substrates, Copper and Aluminum Heat-Sinks, Fixtures, etc.). Applications include LED die (light emitting diodes for example of the lateral, vertical thin film or flip chip varieties) made from various compound semiconductor materials, power die made from silicon, concentrated photovoltaic compound semiconductor cells (e.g. multi-junction cells) silicon carbide and gallium nitride used in power modules, and discretes, MEMS (micro-electromechanical sensor) devices of all types, semiconductor and stacked die, Thermoelectric material element attach to substrates, as well as Piezo-electric element stack attach, and oscillator crystals and optical and other sensor device attach. The attachment of such semiconductor or other die elements may be accomplished by printing on to the substrates, followed by die placement via a die bonder or a pick and place machine, and sintering in either a reflow oven belt oven or box oven. Attachment of such semiconductor and die elements can also be accomplished via dispensing the paste, followed by die placement and sintering as outlined above, or doing film transfer and lamination on the die backside of the film made from the said material, followed by die placement and tacking onto the substrate, followed by sintering. Flip chip die can be assembled by printing bumps on the substrate, placing the die, followed by sintering. Low temperature sintering, and sintering with a regular short lead free reflow profile enables assembly of high CTE mismatch stacks as well as temperature sensitive material stacks. A major benefit of the sintering powder as disclosed herein in such applications is improved throughput with short cycle times while using existing standard installed equipment (such as printers, die bonders and reflow/belt ovens).

(116) B. Attachment of semiconductor packages of various types (for example bottom termination components such as, for example, LGAs, QFNs, QFPs), onto a variety of substrates such as, for example, DBC (Direct Bond Copper), DPC (Direct Plate Copper), MCPCB (Metal Core PCBs), FR4, Flexible PCBs and substrates, Copper and Aluminum Heat-Sinks, Fixtures, etc.). Applications include LED packages of various types (for example, ceramic submount LEDs, SMD LEDs with leadframe construction, etc) power modules, and discretes, MEMS (micro-electromechanical sensor) packages of all types, semiconductor and stacked die packages, Thermoelectric material element attach to substrates, as well as Piezo-electric element stack attach, and oscillator crystals and optical and other sensor device attach. The attachment of such semiconductor or other packages can be accomplished by printing on to the substrates, followed by package placement via standard a pick and place machine with Z Height adjustment and/or pressure capability, and sintering in either a reflow oven belt oven or box oven. Low temperature sintering and sintering with a regular short lead free reflow profile enables assembly of high CTE mismatch stacks as well as temperature sensitive material stacks. A major benefit of the sintering powder as disclosed herein in such applications is improved throughput with short cycle times while using existing standard installed equipment (such as printers, die bonders and reflow/belt ovens).

(117) C. Production of interconnect lines (‘circuitry, pads, etc.) separately and along with flip chip interconnects. For example, applications for interconnect lines include LED boards and luminaires, where the interconnect lines can be applied by a variety of printing (e.g. stencil printing) or dispensing or jetting techniques. In the case of LED applications, such interconnects can serve as both electrical and thermal conductors to carry the electrons to and from the device, and the heat away from the device. Further, such interconnect lines can be directly applied in the same step with interconnects for attaching flip chip or wire bonded devices. Another example of such interconnects is solar cells (either silicon based or thin film based), where the interconnects in a grid pattern could be used to collect electrons generated, and also connect one cell to another. Another example of such applications is an OLED device where a grid of such interconnect lines can be used to enhance the electrical conductivity of transparent conductive films.

(118) D. Wafer-to-wafer bonding layers, based on both printable pastes and films. There is a significant need for wafer-to-wafer bonding at low temperatures (under 250° C.) where the bonding layer exhibits very high temperature properties post bonding. In the case of LED wafer bonding, this can be accomplished for example, in the context of either thin film flip chip or vertical thin film or truncated inverted pyramid LEDs, where CTE mismatch and therefore strain and defect generation can be minimized, while allowing for high temperature post processing with a variety of advanced materials for enhancing light output and electrical efficiency of the device. Further, the high temperature and high thermal and electrical conductivities of the bonding layer allow for superior thermal transfer, high temperature operation of the device and superior current spreading, among other advantages. Such wafer bonding can be accomplished by lamination of films of the said material on the backside of the wafers, followed by temperature and pressure processing in a standard wafer bonder or a press. Another means of doing the processing includes printing a conformal layer of paste on the wafer backside, followed by drying and bonding in a standard wafer bonder or press, under temperature and pressure conditions. Applications for such wafer bonding include power semiconductor wafers, Through Silicon Via (TSV) applications, stacked die applications, MEMS, Thermoelectric Material wafers, Piezo-electric materials, concentrated photovoltaics and other applications. Low temperature sintering enables assembly of high CTE mismatch stacks as well as temperature sensitive material stacks. A major benefit of the sintering powder as disclosed herein in such applications is improved throughput with short cycle times while using existing standard installed equipment (such as printers/laminators, wafer bonders and reflow/belt ovens).

(119) E. Wafer back-side lamination, based on both printable pastes and films. In certain applications there is a need to laminate the back-side of the semiconductor wafers with the solder powder as disclosed herein in paste or film form, prior to drying and dicing. Such an approach can provide a convenient way to apply the die attach material to the wafer prior to mounting on dicing tape and dicing, so that it can be transported to the die bonder with the pre-laminated Supernova N die attach material. Applications for such an approach can include lateral and vertical LED devices, semiconductor die used in power electronics (power modules, and discretes), MEMS (micro-electromechanical sensor) packages of all types, semiconductor and stacked die packages and other applications, Thermoelectric Materials, Piezo-electric element stack attach, and other applications such as oscillator crystals and optical and other sensor device attach.

(120) F. Reflective layer printing for LED and optical applications. The said material can be used to print reflective layers on to substrates such as DBC (Direct Bond Copper), DPC (Direct Plate Copper), MCPCB (Metal Core PCBs), FR4, Flexible PCBs and substrates, Copper and Aluminum Heat-Sinks, Fixtures, etc.), in order to provide light output enhancement and therefore luminous efficacy enhancement of LED and other optical systems. Such reflective layers can be formed via stencil or screen printing, jetting or dispensing or film lamination of the said material. A major benefit of the sintering powder as disclosed herein in such applications is improved throughput with short cycle times while using existing standard installed equipment (such as printers/laminators, wafer bonders and reflow/belt ovens).

(121) G. Hermetic and near hermetic sealing for packages, perimeter seals, etc. for LED, MEMS, optical sensors and oscillator crystals, OLED and PV applications and general semiconductor packaging. There is a significant need for hermetic sealing of LED, OLED, MEMS and thin film PV packages, to protect the devices from moisture ingress. The said material can exhibit hermetic or near hermetic sealing behavior with proper application and sintering. The said material can be applied in various stages of the manufacturing processes for the above devices: Either at the wafer level with wafer bonding, or in the packaging process via film lamination and bonding, or paste jetting/dispensing followed by lid or glass or laminate cover attach and sintering. Low temperature sintering and sintering with a regular short lead free reflow profile enables assembly of high CTE mismatch stacks as well as temperature sensitive material stacks.

(122) H. ACF Replacements. Arrays of bumps of the said material can be delivered to the substrate via stencil printing, bump transfer, or high speed jet dispensing. Such arrays can be used to serve as electrical contacts to assemble devices without explicit high degrees of alignment. Low temperature sintering and sintering with a regular short lead free reflow profile enables such applications. A major benefit of the sintering powder as disclosed herein in such applications is improved throughput with short cycle times while using existing standard installed equipment (such as printers/laminators, wafer bonders and reflow/belt ovens).

(123) The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.