UV curable and electrically conductive adhesive for bonding magnetic disk drive components
View Patent ↗An electrically conductive adhesive includes a resin component, a photoinitiator, and metal-coated polymer beads. The beads have an average diameter and a very narrow size distribution around the average diameter. The adhesive is applied between a read/write head and a suspension to attach the two, and the adhesive is cured by exposure to an illumination and/or heat. A pad spacer is included between the read/write head and the suspension to define a spacing and parallelism therebetween. The beads in the adhesive can form one or more layers between the read/write head and the suspension or can be disordered. The metal coating of the beads provide electrical conductivity between the read/write head and the suspension.
1. A head gimbal assembly for a hard disk drive comprising:
a suspension;
a read/write head attached to the suspension by an electrically conductive adhesive including
a binder having a resin component and a photoinitiator, and
a filler having metal-coated polymer beads dispersed within the binder; and
a pad spacer disposed between the suspension and the read/write head.
2. The head gimbal assembly of claim 1 , wherein the metal-coated polymer beads form one or more layers between the suspension and the read/write head.
3. The head gimbal assembly of claim 1 , wherein the metal-coated polymer beads are disordered.
4. The head gimbal assembly of claim 1 , wherein the resin component includes an unsaturated monomer.
5. The head gimbal assembly of claim 1 , wherein the resin component includes an oligomer.
6. The head gimbal assembly of claim 1 , wherein the resin component includes a mono-functional acrylic monomer.
7. The head gimbal assembly of claim 1 , wherein the resin component includes a di-functional acrylic monomer.
8. The head gimbal assembly of claim 1 , wherein the resin component includes a multi-functional acrylic monomer.
9. The head gimbal assembly of claim 1 , wherein the photoinitiator includes a UV photoinitiator.
10. The head gimbal assembly of claim 1 , wherein the photoinitiator includes a UV photoinitiator and a visible-light photoinitiator.
11. The head gimbal assembly of claim 1 wherein the binder further includes a thermal initiator.
12. The head gimbal assembly of claim 1 wherein the binder further includes an adhesion promoter.
13. The head gimbal assembly of claim 1 wherein the binder further includes a wetting agent.
14. The head gimbal assembly of claim 1 , wherein the metal-coated polymer beads include a polymer with a glass transition temperature below room temperature.
15. The head gimbal assembly of claim 1 , wherein the metal-coated polymer beads include polystyrene.
16. The head gimbal assembly of claim 1 , wherein the metal-coated polymer beads include a layer of a highly conductive and corrosion resistant material.
17. The head gimbal assembly of claim 1 , wherein a ratio by weight of metal-coated polymer beads to binder is between about 20% and about 80%.
18. The head gimbal assembly of claim 1 wherein the filler further includes an electrically conductive material selected from the group consisting of metal flakes, metal powders, metal-coated glass beads, metal-coated flakes, metal-coated mica, and mixtures thereof.
19. The head gimbal assembly of claim 1 wherein the pad spacer includes polyimide.
20. The head gimbal assembly of claim 1 wherein the pad spacer has a height of about 18μ to about 20 μ.
21. A hard disk drive comprising:
a rotary magnetic storage disk; and
a head gimbal assembly for positioning a read/write head proximate to the magnetic storage disk and including
a suspension,
the read/write head attached to the suspension by an electrically conductive adhesive having
a binder having a resin component and a photoinitiator, and
a filler having metal-coated polymer beads dispersed within the binder, and
a pad spacer disposed between the suspension and the read/write head.
22. A method for attaching a read/write head to a suspension, comprising:
providing the suspension including a bonding surface and a pad spacer extending from the bonding surface;
applying to the bonding surface a drop of an electrically conductive adhesive including
a binder having a resin component and a photoinitiator, and
a filler having metal-coated polymer beads dispersed within the binder;
pressing the read/write head against the drop on the bonding surface with a compressive force; and
exposing the adhesive to an illumination.
23. The method for attaching a read/write head to a suspension of claim 22 , wherein the adhesive is applied as a single drop and the single drop of the adhesive is the only adhesive used for said attaching.
24. The method for attaching a read/write head to a suspension of claim 23 , wherein the single drop has a volume on the order of 2 nanoliter or less.
25. The method for attaching a read/write head to a suspension of claim 22 , wherein a bonding surface of the read/write head is metallized.
26. The method for attaching a read/write head to a suspension of claim 22 , wherein the compressive force is no more than 2.5 grams.
27. The method for attaching a read/write head to a suspension of claim 22 , wherein the illumination includes a UV wavelength.
28. The method for attaching a read/write head to a suspension of claim 22 , wherein the illumination includes a broad spectrum between about 250 nm and about 500 nm.
29. The method for attaching a read/write head to a suspension of claim 22 , wherein the illumination has an intensity of between about 1.0 W/cm 2 and about 2.0 W/cm 2 .
30. The method for attaching a read/write head to a suspension of claim 22 , wherein the illumination includes a visible wavelength.
31. The method for attaching a read/write head to a suspension of claim 22 , wherein the adhesive is exposed to the illumination for less than 2 seconds.
32. The method for attaching a read/write head to a suspension of claim 22 , wherein the electrically conductive adhesive further includes a thermal initiator and the method further includes a thermal treatment.
33. The method for attaching a read/write head to a suspension of claim 32 , wherein the thermal treatment is for about 12 minutes at about 120° C.
34. A method for attaching a read/write head to a suspension, comprising:
providing the read/write head including a bonding surface and a pad spacer extending from the bonding surface;
applying to the bonding surface a drop of an electrically conductive adhesive including
a binder having a resin component and a photoinitiator, and
a filler having metal-coated polymer beads dispersed within the binder;
pressing the suspension against the drop on the bonding surface with a compressive force; and
exposing the adhesive to an illumination.