LOW PRESSURE SINTERING POWDER

Abstract

A sintering powder comprising: a first type of metal particles having a mean longest dimension of from 100 nm to 50 μm.

Claims

1. A sintering powder comprising: a particulate, wherein the particulate comprises: from 1 to 19 wt % of a first type of metal particles having a mean longest dimension of from 100 nm to 20 μm, wherein the first type of metal particles is at least partially coated with a first capping agent; and from 81 to 99 wt % of a second type of metal particles having a mean longest dimension of from 5 to 75 nm, wherein the second type of metal particles is at least partially coated with a second capping agent.

2. The sintering powder of claim 1, wherein the first capping agent comprises a carboxylate and/or amine functional group.

3. The sintering powder of claim 1, wherein the first capping agent comprises a straight chain or branched chain aliphatic carboxylic acid.

4. The sintering powder of claim 1, wherein the first capping agent comprises oleic acid.

5. The sintering powder of claim 1, wherein the sintering powder has a total capping agent concentration of up to 5 wt %.

6. The sintering powder of claim 1, wherein the sintering powder has a total capping agent concentration of at least 0.1 wt %.

7. The sintering powder of claim 1, wherein the sintering powder has a total capping agent concentration of from 0.1 to 3 wt % capping agent.

8. The sintering powder of claim 1, wherein the first type of metal particles has a D50 of from 1 to 3 μm.

9. The sintering powder of claim 1, wherein the first type of metal particles has a tap density of from 3.5 to 5.5 g/cc.

10. The sintering powder of claim 1, wherein the first type of metal particles and/or second type of metal particles comprises silver or an alloy or core-shell structures of silver coated particles thereof.

11. The sintering powder of claim 1, wherein the second capping agent comprises an amine and/or a carboxylate functional group.

12. The sintering powder of claim 1, wherein the second capping agent comprises a straight chain or branched chain aliphatic alkylamine.

13. The sintering powder of claim 3, wherein the second capping agent comprises a straight chain or branched chain aliphatic alkylamine.

14. The sintering powder of claim 1, wherein the second capping agent comprises octylamine.

15. The sintering powder of claim 1, wherein the concentration of the first type of metal particles in the particulate is from 1 to 10 wt % and the concentration of the second type of metal particles in the particulate is from 90 to 99 wt %.

16. A sintering film comprising: the sintering powder of claim 1; and a binder.

17. A sintering paste comprising: the sintering powder of claim 1; and a solvent.

18. The sintering paste of claim 17, wherein the sintering paste further comprises at least one of a binder, a rheology modifier, an organosilver compound, an activator, a surfactant, a wetting agent, hydrogen peroxide, and organic peroxide.

19. A light-emitting diode (LED), microelectromechanical system (MEMS), organic light-emitting diode (OLED), photovoltaic cell, or semiconductor comprising the sintering paste of claim 17 or sintered product thereof.

20. A device or material comprising the sintering paste of claim 17 or sintered product thereof, wherein the device or material comprises at least one of: a semiconductor, a power semiconductor wafer, a LED package, a LED die comprised of compound semiconductor materials, a lateral, vertical thin film or flip chip LED, a ceramic sub-mount LED, a SMD LED with lead-frame construction, a power die comprised of silicon, a concentrated photovoltaic compound semiconductor cell, a multi-junction cell, a power module, a power module comprised of silicon carbide and gallium nitride, a discrete device, a MEMS (microelectromechanical sensor), a stacked die, a thermoelectric material, or a piezoelectric material.

21. The device of claim 20, wherein the sintering paste or sintered product thereof is in further contact with a substrate.

22. A method of manufacturing a sintered joint comprising: printing the sintering paste of claim 17 onto a sheet; heating the paste to at least partially remove the solvent and form a sintering film; providing the sintering film in a vicinity of two or more work pieces to be joined; and heating the sintering film to at least partially sinter the metal.

23. A method of die attachment comprising: printing the sintering paste of claim 17 onto a sheet; heating the paste to at least partially remove the solvent and form a sintering film; placing the sintering film between a die and a substrate to be joined; and sintering the sintering film.

24. A method of wafer bonding comprising: printing the sintering paste of claim 17 onto a sheet; heating the paste to at least partially remove the solvent and form a sintering film; placing the sintering film between two or more wafers to be joined; and sintering the sintering film, wherein the sintering is carried out without the application of pressure.

25. A method of transferring a sintering film to a component, comprising: printing the sintering paste of claim 17 onto a sheet; heating the paste to at least partially remove the solvent and form a sintering film; applying the sintering film to a substrate to form an assembly having a sintering film side and a substrate side; contacting the sintering film side of the assembly with a component; heating the assembly to a temperature of from 50 to 200° C.; applying a pressure of from 1 to 5 MPa to the assembly for from 0.1 seconds to 60 minutes; and separating the substrate from the sintering film.

Description

[0151] The invention will now be described with reference to the following non-limiting Figures, in which:

[0152] FIG. 1 shows (a) Large area Ag films (Example 1) prepared using tape caster and inset shows a rectangular piece of the film on PET, (b) optical microscopic image of the free standing dry film of 18-20 20 μm thickness, (c-e) optical microscopic images of free standing dry film of Example 2 on PET (30-40 μm thickness) and (f-g) optical microscopic images of free standing dry film of Example 5 on PET.

[0153] FIG. 2 shows a schematic representation of die-attach processes “Pressure Sintering (PS)” Vs. “Pressure Placement and Pressure-less Sintering (PPPS)” process steps for die-attach application of the sintering film of the present invention.

[0154] FIG. 3 shows a schematic representation of “Pressure Placement and Pressure-less Sintering” process steps for die-attach application of the sintering film of the present invention and its typical process parameters and their interdependencies.

[0155] FIG. 4 shows plots of die-shear of 3 mm×3 mm Ni/Au coated Si dies attached on Ni/Ag coated DBC using the film of Example 2 as a function of a) placement time and b) tool temperature using “Pressure Placement and Pressure-less Sintering Die-attach Process”.

[0156] FIG. 5 shows SEM images of the cross-section area of 3 mm×3 mm Ni/Au coated Si dies attached on Ni/Ag coated DBC using the film of Example 2 at placement time 1s using “Pressure Placement and Pressure-less Sintering Die-attach Process”.

[0157] FIG. 6 shows transferred Ag film on Ni/Au coated Si wafer and remaining film on PET after transfer.

[0158] FIG. 7 shows images of diced (3 mm×3 mm) samples from thermo-compression bonded (a) Ni/Au coated 4″ Si wafer pairs and (b) Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer using 18-20 μm film of Example 2 prepared by commercially available dicing machine. No chipping is observed.

[0159] FIG. 8 shows a C-SAM image of thermo-compression bonded Ni/Au coated 4″ Si wafer pairs using 18-20 μm film of Example 1.

[0160] FIG. 9 shows SEM images of the cross-section area of diced samples revealing BLT and microstructures. These samples were prepared from thermo-compression bonded Ni/Au coated Si wafer pairs using 18-20 μm film of Example 1 at different applied pressures: 0.5 (top left), 1 (top centre), 2 (top right), 5 (bottom left) and 10 MPa (bottom centre).

[0161] FIG. 10 shows C-SAM images of thermo-compression bonded Ni/Au coated 4″ Si wafer pairs using 18-20 μm film of Example 1 without post heating step (step 4).

[0162] FIG. 11 shows representative CSAM image of thermo-compression bonded Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer using 18-20 μm film of Example 1.

[0163] FIG. 12 shows an SEM image of the cross-sectional area of the ion-polished dies prepared from thermo-compression bonded Ni/Au coated 4″ Si wafers using 30-40 μm film of Example 2.

[0164] FIG. 13 shows a C-SAM image of thermo-compression bonded Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer using film of Example 2. The C-SAM image confirms good bonding and there is no delamination or void in the bonded wafers.

[0165] FIG. 14 shows an SEM image of the cross-sectional area of the ion-polished dies prepared from thermo-compression bonded 4″ Si wafer with Ni/Au coated 4″ CuW wafer using 30-40 μm film of Example 2.

[0166] FIG. 15 shows a plot of die-shear of 3 mm×3 mm sized dies prepared from thermo-compression bonded Ni/Au coated 4″ Si wafers pairs and Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW using film of Example 1 and film of Example 2.

[0167] The invention will now be described with reference to the following non-limiting Examples.

EXAMPLE 1

[0168] 0 to 8% resin or polymer, 0 to 2% film forming agent and 5 to 30% solvent mixture were mixed to get a homogeneous solution. To this mixture, 0 to 2% wetting agents, 0 to 2% organic peroxides were added, followed by the addition of 65 to 85% of the aforementioned silver nanopowder (i.e. having a mean longest dimension of from 5 to 75 nm) and was mixed using 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.

EXAMPLE 2

[0169] 0 to 2% film forming agent, 0 to 5% silver metallo organic compound (Ag MOC), 5 to 30% solvent mixture were mixed in a jar. To this mixture, 0 to 2% wetting agents, 0 to 2% organic peroxides were added, followed by the addition of 65 to 85% of the aforementioned silver nanopowder (i.e. having a mean longest dimension of from 5 to 75 nm). This mixture was mixed using 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 3

[0170] 0 to 2% film forming agent, 0 to 8% resin or polymer, 0 to 5% silver metallo organic compounds (Ag MOC) and 5 to 30% solvent mixture were mixed in a jar. To this mixture, 0 to 2% wetting agents, 0 to 2% organic peroxides were added, followed by the addition of 65-85% of the aforementioned silver nanopowder (i.e. having a mean longest dimension of from 5 to 75 nm). This mixture was mixed using 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 4

[0171] 0 to 2% film forming agent, 0 to 8% resin or polymer, 0 to 7% silver metallo organic compounds (Ag MOC) and 5 to 30% solvent mixture were mixed in a jar. To this mixture, 0 to 2% wetting agents, 0 to 2% organic peroxides were added, followed by the addition of 65 to 95% of silver micron particles (i.e. having a mean longest dimension of from 100 nm to 50 μm). This mixture was mixed using an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes.

EXAMPLE 5

[0172] 0 to 2% film forming agent, 0 to 8% resin or polymer, 0 to 7% silver metallo organic compounds (Ag MOC) and 5 to 30% solvent mixture were mixed in a jar. To this mixture, 0 to 2% wetting agents, 0 to 2% organic peroxides were added, followed by the addition of 65-95% of a mixture of silver nano (i.e. having a mean longest dimension of from 5 to 75 nm) and micron particles (i.e. having a mean longest dimension of from 100 nm to 50 μm). This mixture was mixed using an orbital mixer at 1000 rpm. After mixing, the mixture was milled in a three roll mill for a few minutes.

[0173] Thermal conductivity of the sintered silver samples of Examples 1-5 are found to be in the range of 100-250 W.Math.m.sup.−1.Math.K.sup.−1. Thermal conductivity of the sintered silver samples are prepared by heating the paste in Examples 1-5 at 250° C. for 60 min with no applied pressure and are measured using a Netzsch LFA 447 Nanoflash. Thermal conductivity k (W.Math.m.sup.−1.Math.K.sup.−1) was calculated using the following formula: K=α ρ c.sub.p, where, α is thermal diffusivity (m.sup.2.Math.s.sup.−1), p is the density of the material (Kg.Math.m.sup.−3) and c.sub.p is the specific heat capacity (J.Math.kg.sup.−1.Math.K.sup.−1).

Film Preparation Process:

[0174] Films were prepared by printing on silicon coated polyester sheet either using a commercially available tape caster in roll to roll fashion, using a micro gauge controlled doctors blade assembly supplied with the tape caster or by manual stencil printing using a doctor blade.

Commercially Available Tape Caster:

[0175] The paste of Example 1 was printed on a silicon coated polyester sheet using a commercially available tape caster and was dried at 130° C. on its heated surface in roll to roll fashion. For complete drying, the film takes 10 to 15 minutes. The thickness of the film was controlled using the gap setting of the doctor blade assembly supplied with the tape caster. Film thicknesses of 18-20 μm and 33-35 μm were prepared by changing the gap setting of the micro gauge controlled doctor blade assembly. FIG. 1 (a) shows the large area film prepared using tape caster and inset shows a rectangular piece of the film on PET. FIG. 1 (b) shows the optical microscopic image of the free standing dry film of 18-20 20 μm thickness. Films having thickness >5 μm can also be easily obtained by simply changing the gap setting of the doctor blade assembly.

Manual Stencil Printing:

[0176] The paste of Example 2 was manually stencil printed using a doctor blade on silicon coated polyester. These as prepared films were dried at 60-90° C. in an oven for 30-90 minutes. The thickness of such manually printed films of Example 2 is found to be 20-60 μm. Optical microscopic images of free standing dry film of Example 2 and Example 5 on PET (30-40 μm thickness) are shown in FIG. 1 (c-e) and FIG. 1 (f-g) respectively. Alternatively, films also can be printed on silicon coated polyester sheet using a commercially available tape caster in roll to roll fashion and thickness of the film can be controlled using the gap setting of the micro gauge controlled doctor blade assembly supplied with the tape caster.

Application of Ag Films for Die-Attachment:

[0177] The sintering films of the present invention can be used for the joining of electronic components using variety of silver sintering based existing die-attached processes (Pressure Sintering (PS) Process) including those as described in patent application U.S. Ser. No. 13/287,820, the disclosure of which is hereby incorporated by reference. In addition, the sintering films of the present invention can be used in a die attach “Pressure Placement and Pressure-less Sintering (PPPS) process”. FIG. 2 shows the schematic representation of the general process steps of “Pressure Sintering (PS)” Vs. “Pressure Placement and Pressure-less Sintering (PPPS)” process steps using the sintering films of the present invention. There are several additional advantages for this new PPPS process as compared to PS process viz., shorter time required for die-placement (high UPH), low-pressure requirement for placement (highly advantageous for processing thin wafers), compatibility with commercial die-bonder and sintering in external heating equipment (batch process to improve UPH). Additionally, these sinterable Ag films can also be used for PS process that require significantly higher pressure (>5 MPa) during sintering based die-attached processes.

Pressure Placement and Pressure-Less Sintering (PPPS) Process:

[0178] The sintering films of the present invention can be used for the joining of electronic components using a new silver sintering low-temperature and low-pressure die-attach process “Pressure Placement and Pressure-less Sintering (PPPS) process”. FIG. 3 shows the schematic representation of “Pressure Placement and Pressure-less Sintering process” steps for die-attach application of nano-Ag film, its typical process parameters and their interdependence. Joining of electronic components using this Pressure Placement and Pressure-less Sintering process using this sinterable Ag film is very versatile and the exact combination of time, temperature and pressure can be optimized based on the nature of application and thermo-mechanical, electrical and thermal performance requirements.

PPPS Die-Attach Process Steps:

[0179] The overall bonding process may typically include, for example: 1) Film transfer, 2) Pressure Assisted Die Placement and 3) Pressureless Sintering, unless stated otherwise separately elsewhere.

[0180] (1) Film Transfer: Sinterable Ag film transfer on the die by stamping process using optimized combination of time, pressure and temperature of tool and plate. Typical process parameters are:

Tool Temperature: Room Temperature to 400° C.

Plate Temperature: Room Temperature to 400° C.

Pressure: 0.1 to 5 MPa

Time: 0.1 to 60 s

[0181] (2) Pressure Assisted Die Placement: Placement of sinterable Ag containing die on DBC (direct bonded copper) substrate using optimized combination of time, pressure and temperature of tool and plate. Typical process parameters are:

Tool Temperature: Room Temperature to 400° C.

Plate Temperature: Room Temperature to 400° C.

Pressure: 0.1 to 40 MPa

Time: 0.1 to 60 min

[0182] Additional Heating Time: May include additional 0-60 min immediately after placement (without applying any external pressure)

[0183] (c) Pressureless Sintering: Pressureless sintering is carried out in an external oven or hot plate. Process parameters are summarized below:

Sintering Temperature: 150-400° C.

Sintering Time: 0 to 120 min

Pressure Assisted Sintering (PS) Process:

[0184] The sintering films described herein can be used for the joining of electronic components using pressure assisted sintering die-attach process. Joining of electronic components using this pressure assisted sintering process using this sinterable Ag film is very versatile and the exact combination of time, temperature and pressure can be optimized based on the nature of application and thermo-mechanical, electrical and thermal performance requirement.

PS Die-Attach Process Steps:

[0185] The overall bonding process may typically include, for example: 1) Film transfer, 2) Pressure Assisted Die Placement and Sintering, unless stated otherwise separately elsewhere.

[0186] (1) Film Transfer: Sinterable Ag film transfer on the die by stamping process using optimized combination of time, pressure and temperature of tool and plate. Typical process parameters are:

Tool Temperature: Room Temperature to 400° C.

Plate Temperature: Room Temperature to 400° C.

Pressure: 0.1 to 5 MPa

Time: 0.1 to 60 s

[0187] (2) Pressure Assisted Die Placement and Sintering: Placement of sinterable Ag containing die on DBC substrate using optimized combination of time, pressure and temperature of tool and plate. Typical process parameters are:

Tool Temperature: Room Temperature to 400° C.

Plate Temperature: Room Temperature to 400° C.

Pressure: 0.1 to 40 MPa

[0188] Time: 0.1 s to 60 minutes
Additional Heating Time: May include additional 0-60 min immediately after placement (without applying any external pressure)

General Characterization Processes of Bonded Dies:

[0189] The bonded dies were characterized with die-shear, thermal shock and cycling, bond-layer thickness measurements and microstructure analysis, using SEM after ion-polishing.

Die-Attach Application 1 (PPPS):

[0190] The application of the sintering film formed of Example 2 has been demonstrated for the joining of electronic components using a pressure sintering process (Process schematic is shown in FIG. 3). An example of such application has been demonstrated attaching Ni/Au coated 3 mm×3 mm Si dies on Au or Ag coated DBC substrates using sinterable Ag film using a laboratory manual die-bonder. FIG. 4 shows die-shear results of 3 mm×3 mm Ni/Au coated Si dies attached on Ni/Ag coated DBC using the sintering film formed of Example 22 as a function of a) placement time and b) tool temperature using “Pressure Placement and Pressure-less Sintering Die-attach Process”. Following process parameters are used for die-attach:

[0191] (1) Film Transfer:

Tool Temperature: 100-200° C.

Plate Temperature: Room Temperature

Pressure: 1.5 MPa

Time: 1 s

[0192] (2) Pressure Assisted Die Placement:

Tool Temperature: 100-200° C.

Plate Temperature: 200° C.

Pressure: 2

Time: 0.25 to 1.5 s

Additional Heating Time: None

[0193] (3) Pressureless Sintering:

Sintering Temperature: 225° C.

Sintering Time: 60 min

[0194] FIG. 5 shows the SEM images of the cross-sectional area of the ion-polished dies prepared from 3 mm×3 mm Ni/Au coated Si dies attached on Ni/Ag coated DBC using sintering film formed of Example 2 with 1 s placement time. The SEM of the bonding layer shows the necking of the sintered silver particles with a good packing fraction.

Die-Attach Application 2 (PS):

[0195] The application of the sintering film formed of Example 5 has been demonstrated for the joining of electronic components using a pressure assisted sintering process. An example of such application has been demonstrated attaching Ni/Au coated 3 mm×3 mm Si dies on Au or Ag coated DBC or Ag coated Cu lead frames substrates the sintering film formed of Example 5 using a laboratory manual die-bonder by applying sintering pressure 5-20 MPa at 250° C. for 30-90 s sintering time. The die-shear results show strong bonding (>40 MPa) and the SEM of the bonding layer shows the necking of the sintered silver particles with a good packing fraction.

Application of Ag Films for Wafer Bonding:

[0196] Thermo-compression bonding applications of a pair of Ni/Au coated 4″ Si wafers (Si-Sintered Ag—Si) and Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer (Si-Sintered Ag—CuW) are demonstrated using a film formed of Example 1 and a film formed of Example 2 at 250° C. using 1 MPa pressure using a laboratory press. For all of the demonstration of the wafer bonding (application 1-4) using these films, the following bonding processes are followed unless stated otherwise elsewhere.

Wafer Bonding Process Steps:

[0197] The overall bonding process may typically include, for example: 1) Film transfer, 2) Wafer stack formation, 3) Wafer bonding and 4) Post heating, unless stated otherwise separately elsewhere.

1) Film Transfer:

[0198] The Ag film is transferred from PET surface to either Ni/Au coated Si or Ni/Au coated CuW at 80-150° C. and 1 MPa pressure for 5 min. The remaining Ag film and PET were removed and Ag transferred Ni/Au coated Si or Ni/Au coated CuW wafers were used for stack formation. FIG. 6 shows the images of transferred Ag film on Ni/Au coated Si wafer and remaining film on PET after transfer.

2) Wafer Stack Formation:

[0199] Stack is prepared by placing a Ni/Au coated Si wafer on Ag film transferred Ni/Au coated Si or Ni/Au coated CuW by step 1. The stack is then heated at 100-150° C. and 1 MPa pressure for 5-15 min.

3) Wafer Bonding

[0200] Wafers stack processed by step 2 is used for bonding at 250° C. and 1 MPa pressure for 15 min.

4) Post Heating

[0201] Wafers stack processed at 250 by step 3 are used for post heating at 250° C. without any applied pressure for 45 min. After these processes, bonded wafer is cooled to room temperature and used for further characterization.

General Characterization Processes of Bonded Wafers:

[0202] All of the bonded wafers were inspected for delamination and voids using C-SAM. These bonded wafers were then diced to obtain different die sizes, like, 3 mm×3 mm & 10 mm×10 mm for various characterizations, such as die-shear, thermal shock and cycling, bond-layer thickness measurements and microstructure analysis, using SEM after ion-polishing. For example, FIG. 7 shows the images of diced (3 mm×3 mm) samples using commercially available dicing machine prepared from thermo-compression bonded (a) Ni/Au coated 4″ Si wafer pairs and (b) Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer, using 18-20 μm film of Example 1. No de-bonding and chipping are observed for all of these bonded wafers, indicating good bonding.

Wafer Bonding Application 1 (Si-AF1-Si)

Bonding at Different Applied Pressure:

[0203] Thermo-compression bonding of a pair of Ni/Au coated 4″ Si wafers are demonstrated using 18-20 μm film of Example 1 at 250° C. using 0.5, 1, 2 and 5 MPa pressure using a laboratory press. For 10 MPa pressure a pair of Ni/Au coated 2″ Si wafers were used. All of the bonded wafers were inspected for delamination and voids using C-SAM and confirmed there is no-delamination and voids. FIG. 8 shows the C-SAM image of thermo-compression bonded Ni/Au coated 4″ Si wafer pairs using 18-20 μm film of Example 1. The C-SAM image confirms good bonding and there is no delamination and voids in the bonded wafers. These bonded wafers were then diced to different die sizes, like, 3 mm×3 mm, 10 mm×10 mm and used for determining die-shear, bond-layer thickness measurement and microstructure analysis using SEM after ion-polishing. To investigate the effect of the pressure on the microstructure and bond line thickness (BLT) of the sintered silver layers, these wafers were diced and investigated using SEM. FIG. 9 shows the SEM images of the cross-sectional area of the ion-polished dies prepared from thermo-compression bonded pairs Ni/Au coated Si wafers using 18-20 μm film of Example 1 at different applied pressures: a) 0.5, b) 1, c) 2, d) 5 and e) 10 MPa. The SEM of the bonding layer shows the necking of the sintered silver particles with a good packing fraction. The BLT is found highly pressure dependent at the low pressure region (0.5 to 2 MPa), after which the effect of pressure on BLT becomes less prominent. In contrast, the microstructure of these sintered silver are highly pressure dependent throughout the experimentally applied pressure range as evident from the crystallite size, interlinking neighbors and density. As can be seen, at pressures of 5 and 10 MPa, it produces a highly dense and interlinked structure. The die-shear of the bonded dies show bulk or interfacial failure and thus it can be concluded that the sintered silver bonding materials is very strong as compared to the bonded silicon wafer materials.

Bonding without Post Heating:

[0204] To confirm the necessity of the post heating step, we have bonded two pairs of Ni/Au coated 4″ Si wafers using the 18-20 μm film formed of Example 1 at 250° C. using 1 MPa pressure using a laboratory press, without performing post heating step (step 4). As it can be clearly seen in FIG. 10, there are several delaminating areas present in these wafers.

Wafer Bonding Application 2 (Si-AF1-CuW):

[0205] Thermo-compression bonding of Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer are demonstrated using 18-20 μm film formed of Example 1 at 250° C. using 1 MPa pressure using a laboratory press. FIG. 11 shows the C-SAM image of thermo-compression bonded Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer using 18-20 μm film of Example 1. The C-SAM image confirms good bonding and there is no delamination and voids in the bonded wafers. These bonded wafers were then diced to different die sizes like, 3 mm×3 mm & 10 mm×10 mm and used for determining die-shear, bond-layer thickness measurement and microstructure analysis, using SEM after ion-polishing. To investigate the effect of film thickness on the bond line thickness (BLT) of the sintered silver layers, we have chosen 18-20 and 32-35 μm films formed of Example 1 to bond 4″ Si wafer with Ni/Au coated 4″ CuW wafer at 250° C. using 1 MPa pressure using a laboratory press. The SEM of the bonding layer shows the necking of the sintered silver particles with a good packing fraction. The BLT is found to be decreased with decreasing the film thickness. The die-shear of the bonded dies shows bulk or interfacial failure and thus it can be concluded that the sintered silver bonding materials is very strong as compared to the bonded silicon wafer materials.

Wafer Bonding Application 3 (Si-AF2-Si):

[0206] Thermo-compression bonding of a pair of Ni/Au coated 4″ Si wafers are demonstrated using 30-40 μm film of Example 2 at 250° C. using 1 MPa pressure using a laboratory press. All of the bonded wafers were inspected for delamination and voids using C-SAM and confirmed there is no-delamination and voids. C-SAM images of thermo-compression bonded Ni/Au coated 4″ Si wafer pairs using 30-40 μm film of Example 2 confirms good bonding and there is no delamination and voids in the bonded wafers. These bonded wafers were then diced to different die sizes, like, 3 mm×3 mm, 10 mm×10 mm and utilized for die-shear, and bond-layer thickness measurements and microstructure analysis, using SEM after ion-polishing. FIG. 12 shows the SEM images of the cross-sectional area of the ion-polished dies prepared from thermo-compression bonded pairs Ni/Au coated 4″ Si wafers using 30-40 μm film of Example 2 at 1 MPa applied pressure. The SEM of the bonding layer shows the necking of the sintered silver particles with a good packing fraction. The die-shear of the bonded dies show bulk or interfacial failure and thus it can be concluded that the sintered silver bonding materials is very strong as compared to the bonded silicon wafer materials.

Wafer Bonding Application 4 (Si-AF2-CuW):

[0207] Thermo-compression bonding of Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer are demonstrated using 30-40 μm film of Example 2 at 250° C. using 1 MPa pressure using a laboratory press. FIG. 13 shows the C-SAM image of thermo-compression bonded Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer with 30-40 μm film of Example 2. The C-SAM image confirms good bonding and there is no delamination and void in the bonded wafers. These bonded wafers were then diced to different die sizes like, 3 mm×3 mm & 10 mm×10 mm and utilized for die-shear and bond-layer thickness measurements and microstructure analysis using SEM after ion-polishing. FIG. 14 shows the SEM images of the cross-sectional area of the ion-polished dies prepared from thermo-compression bonded 4″ Si wafer with Ni/Au coated 4″ CuW wafer using 30-40 μm film of Example 2 at 250° C. using 1 MPa pressure. The SEM of the bonding layer shows the necking of the sintered silver particles with a good packing fraction. The die-shear, of the bonded dies, shows bulk or interfacial failure and thus, it can be concluded that the sintered silver bonding materials is very strong as compared to the bonded silicon wafer materials.

Mechanical and Thermo-Mechanical Characterization of Bonded Wafers

Die-Shear Results:

[0208] To investigate the mechanical bond strength of bonding sintered Ag layer, the thermo-compression bonded wafers were diced into 3 mm×3 mm sized die and die-shear test performed. The die-shear of the bonded dies show bulk or interfacial failure and thus it can be concluded that the sintered silver bonding materials is very strong as compare to the bonded silicon wafer materials. FIG. 15 shows comparison of the die-shear values of 3 mm×3 mm sized dies prepared from thermo-compression bonded pair of Ni/Au coated 4″ Si wafers and Ni/Au coated 4″ Si wafer with Ni/Au coated 4″ CuW wafer using a film formed of Example 1 and a film formed of Example 2 at 250° C. using 1 MPa pressure.

Thermal Shock Results:

[0209] To investigate the effect of thermal stress on the bonded wafer and dies using sintered nano-sliver films, the thermo-compression bonded 4″ Si wafer with Ni/Au coated 4″ CuW wafer using a film formed of Example 1 and a film formed of Example 2 at 250° C. and 1 MPa pressure and 10 mm×10 mm dies were subjected to thermal shock experiments following the JESD22-A104-B Test Condition B, Soak Mode 2 (−55 to +125° C., 5 mins dwell time, 1000 cycles). The C-SAM images of both the bonded wafers and dies post 1000 cycles do not reveal any delamination, voids and cracks in the bonded wafers.

Thermal Cycling Results:

[0210] To investigate the effect of thermal stress on the bonded dies using sintered nano-sliver films, 10 mm×10 mm diced samples from the thermo-compression bonded 4″ Si wafer with Ni/Au coated 4″ CuW wafer using film formed of Example 1 and film formed of Example 2 at 250° C. and 1 MPa pressure were subjected to thermal cycling experiments following the IPC 9701-A Standard TC3/NTC-C Profile (−40 to +125° C., 15 mins dwell time, 1000 cycles). The C-SAM images of these dies post 1000 cycles do not reveal any delamination, voids and cracks in the bonded wafers.

[0211] Other applications of the sintering powders, sintering films and sintering pastes of the present invention are as follows:

[0212] 1. Wafer-to-wafer bonding layers for Vertical LED Designs, Thin Film Flip Chip Designs and Red LED Designs, based on both printable pastes and films. There is a significant need for wafer-to-wafer bonding at low temperatures (under 250° C. and also under 200° 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. Other applications for such wafer bonding include power semiconductor wafers, Through Silicon Via (TSV) applications, stacked die applications, MEMS, concentrated photovoltaic and other applications. Low temperature sintering enables assembly of high CTE mismatch stacks as well as temperature sensitive material stacks, thermoelectric materials and piezoelectric materials.

[0213] 2. 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 discrete devices, MEMS (microelectromechanical sensor) devices of all types, semiconductor and stacked die and other applications such as thermoelectric materials and piezoelectric materials. [0214] (a) The attachment of such semiconductor or other die elements can 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 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 enables assembly of high CTE mismatch stacks as well as temperature sensitive material stacks.

[0215] 3. Attachment of semiconductor packages of various types (for example bottom termination components such as LGAs, QFNs, QFPs, etc.), onto a variety of 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.). Applications include LED packages of various types (for example, ceramic sub-mount LEDs, SMD LEDs with lead-frame construction, etc,) power modules, and discrete devices, MEMS (microelectromechanical sensor) packages of all types, semiconductor and stacked die packages and other applications. [0216] (a) The attachment of such semiconductor or other packages can be accomplished by printing on to the substrates, followed by package placement via standard 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 enables assembly of high CTE mismatch stacks as well as temperature sensitive material stacks.

[0217] 4. 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.

[0218] 5. 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.

[0219] 6. Hermetic and near hermetic sealing for packages, perimeter seals, etc. for LED, MEMS, 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 enables assembly of high CTE mismatch stacks as well as temperature sensitive material stacks.

[0220] 7. 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