Optimization of desiccant usage in a MEMS package

• US 8,435,838 B2
• Filed: 09/28/2007
• Issued: 05/07/2013
• Est. Priority Date: 09/28/2007
• Status: Expired due to Fees

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: He, Rihui, Wu, Lingling, Palmateer, Lauren, Heald, David, Lin, Yen Hua
• Primary Examiner(s): GREEN, TELLY D
• Application Number:
  US12/680,503
• Publication Number:
  US 20110012219A1
• Time in Patent Office: 2,048 Days
• Field of Search: 438106-127, 359/245, 359/247
• US Class Current: 438/126
• CPC Class Codes: B81C 1/00285 using materials for controlling the level of pressure, contaminants or moisture inside of the package, e.g. getters
• CPC Class Codes: B81C 1/00674 Treatments for improving wear resistance

Abstract

A MEMS device may be package with a desiccant to provide a moisture-free environment. In order to avoid undesirable effects on the MEMS device, the desiccant may be selected or treated so as to be compatible with a particular MEMS device. This treatment may include baking of the desiccant to as to cause outgassing of moisture or other undesirable material. The structure of the MEMS device may also be altered to improve compatibility with particular desiccants.

Claims

1. A method of encapsulating a MEMS device, the method comprising:

providing a substrate supporting a MEMS device;

providing a backplate;

providing a desiccant, said desiccant comprising calcium oxide and polytetrafluoroethylene;

baking said desiccant under conditions sufficient to cause outgassing of organics retained therein, wherein baking said desiccant under conditions sufficient to cause outgassing of organics retained therein comprises heating said desiccant beyond what is necessary to cure said desiccant; and

sealing said backplate to said substrate to form a MEMS package encapsulating the MEMS device and the desiccant.

2. The method of claim 1, wherein baking said desiccant comprises baking said desiccant at a temperature higher than about 105°

C.

3. The method of claim 2, wherein baking said desiccant comprises baking said desiccant at a temperature higher than about 120°

C.

9. The method of claim 1, wherein heating said desiccant beyond what is necessary to cure said desiccant includes heating said desiccant at a temperature above the temperature required to cure the desiccant.

10. The method of claim 1, wherein heating said desiccant beyond what is necessary to cure said desiccant includes heating said desiccant at a temperature at least twice the temperature required to cure the desiccant.

11. The method of claim 1, wherein heating said desiccant beyond what is necessary to cure said desiccant includes heating said desiccant for a period longer than required to cure the desiccant.

12. The method of claim 1, wherein heating said desiccant beyond what is necessary to cure said desiccant includes heating said desiccant for a period at least six times longer than required to cure the desiccant.

4. A method of encapsulating a MEMS device, the method comprising:

providing a substrate supporting a MEMS device;

providing a backplate;

providing a desiccant, said desiccant comprising calcium oxide and a polymer binding;

baking said desiccant under conditions sufficient to cause outgassing of solvents retained therein, wherein baking said desiccant under conditions sufficient to cause outgassing of solvents retained therein comprises heating said desiccant beyond what is necessary to cure said desiccant; and

sealing said backplate to said substrate to form a MEMS package encapsulating the MEMS device and the desiccant.

5. The method of claim 4, wherein providing a desiccant comprises providing a desiccant in paste form, and wherein baking said desiccant comprising baking said desiccant at a temperature higher than that required to solidify the desiccant.

6. The method of claim 4, wherein providing a desiccant comprises providing a desiccant in paste form, and wherein baking said desiccant comprising baking said desiccant for a duration longer than that required to solidify the desiccant.

7. The method of claim 4, wherein baking said desiccant comprises baking said desiccant at a temperature higher than about 220°

C.

8. The method of claim 7 wherein baking said desiccant comprises baking said desiccant at a temperature higher than about 280°

C.

13. The method of claim 4, wherein heating said desiccant beyond what is necessary to cure said desiccant includes heating said desiccant at a temperature above the temperature required to cure the desiccant.

14. The method of claim 4, wherein heating said desiccant beyond what is necessary to cure said desiccant includes heating said desiccant at a temperature at least twice the temperature required to cure the desiccant.

15. The method of claim 4, wherein heating said desiccant beyond what is necessary to cure said desiccant includes heating said desiccant for a period longer than required to cure the desiccant.

16. The method of claim 4, wherein heating said desiccant beyond what is necessary to cure said desiccant includes heating said desiccant for a period at least six times longer than required to cure the desiccant.