High-resolution soldering

Patent metadata

Field	Value
Publication number	US-11627667-B2
Application number	US-202117162835-A
Country	US
Kind code	B2
Filing date	Jan 29, 2021
Priority date	Jan 29, 2021
Publication date	Apr 11, 2023
Grant date	Apr 11, 2023

Abstract

A method for circuit fabrication includes defining a solder bump, including a specified solder material and having a specified bump volume, to be formed at a target location on an acceptor substrate. A transparent donor substrate, having a donor film including the specified solder material, is positioned such that the donor film is in proximity to the target location on the acceptor substrate. A sequence of pulses of laser radiation is directed to pass through the first surface of the donor substrate and impinge on the donor film so as to induce ejection from the donor film onto the target location on the acceptor substrate of a number of molten droplets of the solder material such that the droplets deposited at the target location cumulatively reach the specified bump volume. The target location is heated so the deposited droplets melt and reflow to form the solder bump.

First claim

The invention claimed is:

1. A method for circuit fabrication, comprising: defining a solder bump, comprising a specified solder material and having a specified bump volume, to be formed at a target location on an acceptor substrate;
positioning a transparent donor substrate having opposing first and second surfaces and a donor film comprising the specified solder material on the second surface such that the donor film is in proximity to the target location on the acceptor substrate;
directing a sequence of pulses of laser radiation to pass through the first surface of the donor substrate and impinge on the donor film so as to induce ejection from the donor film onto the target location on the acceptor substrate of a number of molten droplets of the solder material such that the droplets deposited at the target location cumulatively reach the specified bump volume; and
heating the target location so that the deposited droplets melt and reflow to form the solder bump.

2. The method according to claim 1 , wherein the droplets have respective droplet volumes that depend on an intensity of the pulses of the laser radiation, and wherein directing the sequence of the pulses comprises setting the intensity of the pulses of laser radiation and the number of the pulses in the sequence responsively to the specified bump volume.

3. The method according to claim 2 , wherein the droplet volumes further depend on a set of pulse parameters consisting of a spot size and duration of the pulses of the laser radiation, and wherein directing the sequence of the pulses further comprises adjusting the droplet volumes by varying one or more of the pulse parameters.

4. The method according to claim 1 , wherein defining the solder bump comprises defining first and second solder bumps, having different, respective first and second bump volumes, at different, respective first and second target locations on the same acceptor substrate, and
wherein directing the sequence of pulses comprises directing different, first and second sequences of the pulses to pass through different points on the donor substrate so that the droplets cumulatively reach each of the different first and second bump volumes at the respective first and second target locations.

5. The method according to claim 4 , wherein defining the first and second solder bumps comprises specifying different, respective first and second compositions of the first and second solder bumps, and wherein positioning the transparent donor substrate comprises providing one or more donor films comprising a plurality of different solder materials selected so as to produce the first and second compositions.

6. The method according to claim 1 , wherein defining the solder bump comprises defining first and second solder bumps, having different, respective first and second compositions, and wherein positioning the transparent donor substrate comprises providing one or more donor films comprising a plurality of different solder materials so as to produce the first and second compositions.

7. The method according to claim 1 , wherein defining the solder bump comprises specifying a composition of the solder bump that includes different, first and second materials, and
wherein positioning the transparent donor substrate comprises providing first and second donor films comprising the first and second materials, respectively, and
wherein directing the sequence of pulses comprises directing first and second sequences of the pulses to impinge respectively on the first and second donor films so that the droplets deposited at the target location cumulatively reach the specified composition.

8. The method according to claim 7 , wherein specifying the composition comprises specifying a gradient of the materials in the composition of the solder bump, and wherein directing the first and second sequences of the pulses comprises depositing the droplets of the first and second materials in multiple layers on the target location in accordance with the specified gradient.

9. The method according to claim 1 , wherein directing the sequence of the pulses comprises depositing the droplets in multiple layers on the target location so as to reach the specified bump volume.

10. The method according to claim 9 , wherein heating the target location comprises alternately depositing a layer of droplets and heating the layer to melt the droplets multiple times until the specified bump volume is reached.

11. The method according to claim 1 , wherein defining the solder bump comprises specifying a shape of the solder bump, and wherein directing the sequence of the pulses comprises depositing the molten droplets in a pattern that conforms to the specified shape.

12. The method according to claim 1 , wherein heating the target location comprises directing a laser beam to irradiate the target location with sufficient energy to cause the deposited droplets to melt and reflow.

13. The method according to claim 1 , and comprising printing a conductive pad at the target location on the acceptor substrate using a process of laser-induced forward transfer (LIFT), wherein directing the sequence of the pulses comprises depositing the molten droplets of the solder material on the printed conductive pad.

14. The method according to claim 13 , wherein printing the conductive pad comprises forming a concavity in the conductive pad for deposition of the molten droplets therein.

15. A system for circuit fabrication, comprising:
a controller, which is configured to receive a definition of a solder bump, comprising a specified solder material and having a specified bump volume, to be formed at a target location on an acceptor substrate;
a printing station, which comprises:
a transparent donor substrate, which has opposing first and second surfaces and has a donor film comprising the specified solder material disposed on the second surface, and which is positioned such that the donor film is in proximity to the target location on the acceptor substrate; and
a laser, which is configured to direct a sequence of pulses of laser radiation to pass through the first surface of the donor substrate and impinge on the donor film so as to induce ejection of molten droplets of the solder material from the donor film onto the target location on the acceptor substrate,
wherein the controller is configured to drive the printing station to eject a number of the droplets toward the target location such that the droplets deposited at the target location cumulatively reach the specified bump volume; and
a reflow station configured to heat the target location so that the deposited droplets melt and reflow to form the solder bump.

16. The system according to claim 15 , wherein the droplets have respective droplet volumes that depend on an intensity of the pulses of the laser radiation and on a set of pulse parameters consisting of a spot size and duration of the pulses of the laser radiation, wherein the controller is configured to set the intensity of the pulses of laser radiation and the number of the pulses in the sequence responsively to the specified bump volume, and wherein the controller is configured to adjust the droplet volumes by varying one or more of the pulse parameters.

17. The system according to claim 15 , wherein the controller is configured to receive definitions of first and second solder bumps, having different, respective first and second bump volumes, at different, respective first and second target locations on the same acceptor substrate, and wherein the controller is configured to drive the laser to direct di

Assignees

• Orbotech Ltd

Inventors

• Kotler Zvi
• Fogel Ofer

Classifications

• H10W72/0711

  Apparatus therefor · CPC title

• H10W72/072

  of bump connectors · CPC title

• H10W72/241

  Dispositions, e.g. layouts · CPC title

• H10W72/012

  of bump connectors, dummy bumps or thermal bumps · CPC title

• H10W72/01225

  in solid form, e.g. by using a powder or by stud bumping · CPC title