System for removing flux residues from printed wiring assemblies

• US 5,045,117 A
• Filed: 09/18/1990
• Issued: 09/03/1991
• Est. Priority Date: 09/18/1990
• Status: Expired due to Fees

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Witherell, Donald R.
• Primary Examiner(s): Morris, Theodore
• Assistant Examiner(s): EL ARINI, ZEINAB
• Application Number:
  US07/586,099
• Time in Patent Office: 350 Days
• Field of Search: 134/21, 134/25.4, 134/95, 134/108, 134/109
• US Class Current: 134/21
• CPC Class Codes: B08B 3/08 the liquid having chemical or dissolving effect substances used, see the relevant classes
• CPC Class Codes: C23G 5/04 Apparatus
• CPC Class Codes: H05K 2203/0783 Using solvent, e.g. for cleaning; Regulating solvent content of pastes or coatings for adjusting the viscosity
• CPC Class Codes: H05K 2203/085 Using vacuum or low pressure
• CPC Class Codes: H05K 2203/1509 Horizontally held PCB
• CPC Class Codes: H05K 3/26 Cleaning or polishing of the conductive pattern

Abstract

A method and apparatus are provided for cleaning rosin flux residues off of printed wiring assemblies. In accordance with the invention printed wiring assemblies are placed within a processing chamber and a vacuum pump is used to draw a vacuum within the processing chamber. The rosin flux residues are then washed off of the printed wiring assemblies using a solvent for dissolving and removing the flux residues.

Claims

1. A process for cleaning rosin flux residues from printed wiring assemblies, comprising the steps of:

placing one or more printed wiring assemblies in a vacuum sealable processing chamber;

drawing down the ambient pressure within said chamber to achieve a partial vacuum in order to promote the migration of flux residues out of confined spaces on said assemblies;

washing said wiring assemblies with solvent to remove flux residues which have migrated out of confined spaces on said assemblies; and

drawing down the ambient pressure within said chamber to achieve a partial vacuum for a second time in order to evacuate any remaining solvent materials from on said assemblies.

2. The process of claim 1, wherein the step of washing said wiring assemblies includes the substeps of:

flooding said chamber with solvent,

flushing solvent through said chamber, and

purging said chamber of solvent.

3. The process of claim 1, wherein said partial vacuums approach 1 mm of Mercury.

4. The process of claim 1, wherein said steps of drawing down the pressure in said chamber include the substep of:

collecting vapor phase solvent drawn out of said chamber in a cold trap.

5. A system for cleaning rosin flux residues from printed wiring assemblies, comprising:

a sealable processing chamber adapted for holding a plurality of wiring assemblies and for maintaining a partial vacuum during processing operations;

vacuum pump means for drawing down the ambient pressure within said chamber in order to promote the migration of flux residues out of confined spaces on said wiring assemblies; and

means for washing said assemblies with solvent in order to remove flux residues which have migrated out of confined spaces on said wiring assemblies.

6. The system of claim 5, wherein said means for washing includes:

means for flooding solvent into said chamber and purging solvent out of said chamber.

7. The system of claim 6, wherein said means for flooding and purging solvent includes one or more liquid phase pumps which are further operative for flushing solvent through said chamber.

8. The system of claim 5 further including:

a cold trap for collecting vapor phase solvent pumped out of said chamber during vacuum pump operations.

9. A process for cleaning rosin flux residues from printed wiring assemblies having SMDs installed thereon, comprising the steps of:

placing one or more wiring assemblies in a vacuum sealable processing chamber;

drawing down the ambient pressure within said chamber by pumping air out of said chamber with a vacuum pump in order to promote the migration of flux residues out from under the SMDs installed on said assemblies;

washing said wiring assemblies with solvent to remove the flux residues which have migrated out from under the SMDs.

10. The process of claim 9, further including the step of:

drawing down the ambient pressure within said chamber by pumping air out of said chamber for a second time in order to evacuate any remaining solvent materials from on said assemblies.

11. The process of claim 9, wherein the step of washing said wiring assemblies includes the substeps of:

flooding said chamber with solvent,

flushing solvent through said chamber, and

purging said chamber of solvent.

12. The process of claim 9, wherein the ambient pressure within said chamber is drawn down to a partial vacuum approaching 1 mm of Mercury.

13. The process of claim 12, wherein said steps of drawing down the pressure within said chamber include the substep of:

collecting vapor phase solvent pumped out of said chamber in a cold trap.