Light emitting diode print head

• US 5,235,347 A
• Filed: 05/13/1991
• Issued: 08/10/1993
• Est. Priority Date: 09/07/1990
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Lee, Choo Boo
• Primary Examiner(s): Fuller, Benjamin R.
• Assistant Examiner(s): YOCKEY, DAVID F
• Application Number:
  US07/699,099
• Time in Patent Office: 820 Days
• Field of Search: 346/107 R, 346/145, 346/139 R, 361/386, 361/387, 361/388, 361/389
• US Class Current: 347/238
• CPC Class Codes: B41J 2/45 using light-emitting diode [LED] or laser arrays

Abstract

A light emitting diode print head has an aluminum substrate or mother plate. A plurality of stainless steel tiles are assembled in a row on the substrate. Each of the tiles has a row of dice, each of which has a row of light emitting diodes. The tiles are assembled so that the LEDs are in a row extending across the print head with the adjacent LEDs at the edges of each of tile being a short distance apart. Compensation for differences in coefficient of thermal expansion between the tiles and substrate is provided by a pair of stainless steel strips adhesively bonded between the tiles and substrate. Each strip is bonded along an edge of the row of tiles away from the row of LEDs by a compliant adhesive. A thermally conductive compliant adhesive is provided between the tiles and substrate beneath the LEDs for heat transfer. The stainless steel strips serve as compensation for the difference in coefficient of thermal expansion between the tiles and substrate. There is a yield increase in print heads of at least 10% without any significant cost increase.

Claims

1. A light emitting diode print head comprising:

an aluminum alloy substrate;

a plurality of flat stainless steel tiles extending in a row on the substrate, each of said tiles including a plurality of light emitting diodes on a face of each of said tiles opposite to the face of the tile which is adjacent to the substrate and having a coefficient of thermal expansion different from a coefficient of thermal expansion of the aluminum substrate and closer to a coefficient of thermal expansion of the light emitting diodes; and

a stainless steel thermal compensation layer having a coefficient of thermal expansion similar to the coefficient of thermal expansion of each of the tiles, the thermal compensation layer being adhesively bonded between the substrate and the tiles by a compliant pressure sensitive adhesive layer between the thermal compensation layer and the substrate, and a compliant adhesive layer between the thermal compensation layer and the tiles.

2. A light emitting diode print head as recited in claim 1 comprising a compliant adhesive layer between the thermal compensation layer and the tiles.

3. A light emitting diode print head as recited in claim 1 wherein the thermal compensation layer has a thickness of about 50 micrometers.

4. A light emitting diode print head as recited in claim 1 further comprising a compliant adhesive layer extending directly between the substrate and a portion of each of the tile opposite to the light emitting diodes.

5. A light emitting diode print head as recited in claim 1 wherein the thermal compensation layer comprises a pair of metal strips spaced apart from each other along edges of the tiles with the light emitting diodes being in a middle portion of the tiles between the edges of the tiles adjacent to the strips.

6. A light emitting diode print head comprising:

an elongated metal substrate;

a row of metal tiles along the metal substrate, the metal tiles each having a coefficient of thermal expansion different from a coefficient of thermal expansion of the metal substrate;

a row of light emitting diode dice on each of the metal tiles, the row of dice on each of the tiles collectively forming a row of light emitting diode dice extending along the length of the substrate;

a pair of metal shims extending along the length of the substrate, each each of the metal shims being between the tiles and the substrate along a portion of the tiles remote from the light emitting diode dice and having a coefficient of thermal expansion similar to the coefficient of thermal expansion of the tiles;

means for adhesively bonding the metal shims to the substrate and for adhesively bonding the tiles to the shims; and

a layer of compliant adhesive for thermal transfer directly between the substrate and a portion of the tiles opposite the light emitting diode dice.

7. A light emitting diode print head as recited in claim 6 wherein the substrate comprises an aluminum alloy, the tiles comprise stainless steel, and the shims comprise stainless steel.

8. A light emitting diode print head as recited in claim 7 wherein the shims each have a thickness of about 50 micrometers.

9. A light emitting diode print head comprising:

an elongated aluminum alloy substrate;

a row of substantially rectangular stainless steel tiles extending along the length of the aluminum substrate on a front face of the substrate;

a row of light emitting diode dice extending across a center portion of a front face of each of the tiles, the row of dice on each of the tiles collectively forming a row of light emitting diode dice extending along the length of the substrate;

a pair of stainless steel shims extending along the length of the substrate, each metal shim being between the front face of the substrate and an edge of the tiles remote from the light emitting diode dice;

compliant means for adhesively bonding the metal shims to the front face of the substrate;

means for adhesively bonding back faces of the tiles to the shims; and

a compliant adhesive layer directly between the substrate and a portion of the tiles opposite the light emitting diode dice for transferring heat.

10. A light emitting diode print head as recited in claim 9 wherein each of the shims has a thickness of about 50 micrometers.

11. A light emitting diode print head as recited in claim 9 wherein the means for bonding the shims to the substrate comprises a pressure sensitive adhesive.

12. A light emitting diode print head as recited in claim 9 wherein the stainless steel of each of the shims is identical to the stainless steel of the tiles.

13. A light emitting diode print head as recited in claim 9 wherein the stainless steel of each of the shims is different from the stainless steel of the tiles and has a coefficient of thermal expansion intermediate between the coefficients of thermal expansion of the steel of the tiles and the aluminum of the substrate.

14. A light emitting diode print head comprising:

an aluminum alloy substrate;

a plurality of stainless steel tiles extending in a row along the substrate;

a plurality of light emitting diode dice arranged in a row on each of the tiles, each of said light emitting diode dice having a row of light emitting diodes collectively forming a row of light emitting diodes on the row of tiles with light emitting diodes in the collective row being equal distances apart;

a pair of strips of metal, each of the strips extending along a lateral edge of the row of tiles, with a gap between the metal strips underlying the row of light emitting diode dice forming a thermal compensation layer between the substrate and the tiles and having a coefficient of thermal expansion different from a coefficient of thermal expansion of the substrate and closer to a coefficient of thermal expansion of the tiles;

a compliant adhesive layer between the thermal compensation layer and the substrate;

a compliant adhesive layer between the thermal compensation layer and the tiles; and

a layer of compliant adhesive between the tiles and the substrate in the gap.

15. A light emitting diode print head as recited in claim 14 wherein the thermal compensation layer has a coefficient of thermal expansion approximately equal to the coefficient of thermal expansion of the tiles.

16. A light emitting diode print head as recited in claim 14 wherein the thermal compensation layer has a coefficient of thermal expansion intermediate between the coefficient of thermal expansion of the tiles and the coefficient of thermal expansion of the substrate.

17. A light emitting diode print head as recited in claim 14 wherein the adhesive layer between the thermal compensation layer and the substrate comprises a pressure sensitive adhesive.

18. A light emitting diode print head comprising:

an elongated metal substrate;

a row of metal tiles along the metal substrate, the metal tiles having a coefficient of thermal expansion different from a coefficient of thermal expansion of the metal substrate;

a row of light emitting diode dice on each of the metal tiles, the row of dice on each of the tiles collectively forming a row of light emitting diode dice extending along the length of the substrate;

a pair of metal shims extending along the length of the substrate, each of the metal shims being between the tiles and the substrate along a portion of the tiles remote from the light emitting diode dice and having a coefficient of thermal expansion intermediate between the coefficient of thermal expansion of the tiles and the coefficient of thermal expansion of the substrate;

a compliant pressure sensitive adhesive layer for adhesively bonding the metal shims to the substrate;

a compliant adhesive layer for adhesively bonding the tiles to the shims; and

a compliant adhesive layer between the tiles and the substrate beneath the row of light emitting diode dice in a gap between the shims for thermal transfer directly between the substrate and a portion of the tiles opposite the light emitting diode dice.

19. A light emitting diode print head as recited in claim 18 wherein the shims have a coefficient of thermal expansion approximately equal to the coefficient of thermal expansion of the tiles and significantly different from the coefficient of thermal expansion of the substrate.