Composite polymer/desiccant coatings for IC encapsulation

• US 4,977,009 A
• Filed: 03/06/1990
• Issued: 12/11/1990
• Est. Priority Date: 12/16/1987
• Status: Expired due to Fees

• Current Assignee: Ford Motor Company
• Original Assignee: Ford Motor Company
• Inventors: Anderson, James E., Troyk, Philip R., Markovac, Vlado
• Primary Examiner(s): Buffalow, Edith
• Application Number:
  US07/489,159
• Time in Patent Office: 280 Days
• Field of Search: 428/76, 428/901, 428/209, 428/446, 428/448, 428/450, 428/447, 428/913, 428/413, 428/423.3, 428/425.5, 174/52 FP, 174/68.5, 361/397
• US Class Current: 428/76
• CPC Class Codes: C09D 183/04 Polysiloxanes
• CPC Class Codes: H01L 23/293 Organic, e.g. plastic
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: Y10S 428/901 Printed circuit
• CPC Class Codes: Y10S 428/913 Material designed to be responsive to temperature, light, moisture
• CPC Class Codes: Y10T 428/239 Complete cover or casing
• CPC Class Codes: Y10T 428/24917 including metal layer
• CPC Class Codes: Y10T 428/31511 Of epoxy ether
• CPC Class Codes: Y10T 428/31554 Next to second layer of polyamidoester
• CPC Class Codes: Y10T 428/31598 Next to silicon-containing [silicone, cement, etc.] layer
• CPC Class Codes: Y10T 428/31663 As siloxane, silicone or silane

Abstract

This invention is directed to composite coating for maintaining low moisture levels at the surface of solid substrates. One embodiment of the invention comprises a coating having a desiccant layer between layers of the same or different elastomeric polymers. Another embodiment comprises a layer of elastomeric polymer covered with a layer of an elastomeric polymer/desiccant mixture. The composite coating may be applied to integrated circuits to prevent corrosion thereof.

Claims

1. A composite coating for maintaining low moisture levels at the surface of solid substrates, which composite coating comprises:

a substantially continuous first layer comprising first elastomeric polymer on said substrate, said first elastomeric polymer being substantially non-reactive with said substrate and being present in a thickness of at least about 0.1 millimeter;

a substantially continuous second layer, on said first layer, comprising a mixture of desiccant and second elastomeric polymer having low permeability to water.

2. The composite coating according to claim 1, wherein said first elastomeric polymer is selected from the group consisting of:

silicone elastomers, epoxy resins, vinyl plastisols and polyurethane.

3. The composite coating according to claim 1, wherein said first layer is present in a thickness between about 0.1 and about 10 millimeters.

4. The composite coating according to claim 1, wherein said first elastomeric polymer is substantially non-electronically conductive.

5. The composite coating according to claim 1, wherein said desiccant is selected from the group consisting of:

silica gel, activated alumina, anhydrous calcium sulfate, magnesium perchlorate and hygroscopic salts wherein saturated solution of said hygroscopic salt corresponds to a relative humidity of less than about 50 percent.

6. The composite coating according to claim 5, wherein said hygroscopic salt is selected from the group consisting essentially of:

calcium chloride, magnesium nitrate, sodium acetate, lithium chloride, and their salt hydrates.

7. The composite coating according to claim 5, wherein a saturated solution of said hygroscopic salt corresponds to a relative humidity between about 10 and about 30 percent.

8. The composite coating according to claim 1, wherein said second elastomeric polymer is selected from the group consisting essentially of polysiloxane, polyurethane rubbers, epoxy resins and vinyl plastisols.

9. The composite coating according to claim 1, wherein said second elastomeric polymer has a water permeability of less than 0.1 mg-mm/cm-day.