Compact convection drying chamber for drying printed circuit boards and other electronic assemblies by enhanced evaporation

• US 6,760,981 B2
• Filed: 01/18/2002
• Issued: 07/13/2004
• Est. Priority Date: 01/18/2002
• Status: Expired due to Term

• Current Assignee: Electrovert U.S.A. Corp., KPS Special Situations Fund II, L.P.
• Original Assignee: Speedline Technologies Incorporated (Illinois Tool Works Inc.)
• Inventors: Leap, Gerald
• Primary Examiner(s): Bennett, Henry
• Assistant Examiner(s): Ragonese, Andrea M.
• Application Number:
  US10/051,213
• Publication Number:
  US 20030136019A1
• Time in Patent Office: 907 Days
• Field of Search: 345/49, 345/52--54, 34/83, 34/84, 341/07, 342/01, 342/02, 342/09--12, 342/15--21, 342/23--25, 342/30--33
• US Class Current: 34/210
• CPC Class Codes: F26B 15/18 the objects or batches of materials being carried by endless belts
• CPC Class Codes: F26B 21/004 Nozzle assemblies; Air knives; Air distributors; Blow boxes F26B3/082, F26B13/104, F26B13/108, F26B21/006 take precedence
• CPC Class Codes: H05K 3/227 Drying of printed circuits

Abstract

The invention provides a compact drying chamber for drying printed circuit boards and electronic connectors and components mounted thereto by enhanced evaporation to remove residual water and completely dry printed circuit boards. The compact drying chamber comprises features that help maximize a velocity at which heated air impacts printed circuit boards to significantly enhance evaporation from surfaces of printed circuit boards and to raise the temperature of electronic connectors and components to allow evaporation therefrom, while maintaining low power consumption with respect to heating and circulating air. The compact drying chamber also comprises features that help maximize a dwell time of printed circuit boards in high velocity heated air within practical conveyance speeds, while maintaining overall dimensions that allow a compact design. The compact drying chamber further comprises features that recirculate air, minimize heat loss, minimize exhaust requirements and keep manufacturing and operation costs low.

Claims

1. A chamber for drying printed circuit boards and other electronic assemblies by convection heating comprising:

a housing defined by an upper wall portion and a lower wall portion, each wall portion having a length and a width, and a first side wall and a second side wall, each side wall connecting the upper wall portion to the lower wall portion; and

at least a first drying zone disposed in the housing, the first drying zone including;

(i) a first gas distribution duct defined by the upper wall portion and a first discharge plate, the first discharge plate spaced from and below the upper wall portion and having a length extending along at least a portion of the length of the upper wall portion and a width extending along at least a portion of the width of the upper wall portion,

(ii) a conveyor spaced from and below the first discharge plate, the conveyor extending at an orientation substantially parallel to the first discharge plate from an inlet at a first end of the housing to an exit at a second end of the housing to convey the printed circuit boards and other electronic assemblies through the first drying zone and to define a product path area between the first discharge plate and the conveyor,

(iii) a plurality of slots defined in the first discharge plate and configured to allow gas within the first distribution duct to vent from the first gas distribution duct, each slot being defined in the first discharge plate in an orientation substantially perpendicular to the direction in which the conveyor conveys the printed circuit boards and other electronic assemblies;

(iv) a gas intake disposed in a side chamber, the gas intake being adjacent and facing the conveyor and extending along at least a portion of the first drying zone, the side chamber being defined between the first side wall of the housing and the gas intake and extending along an interior length of the housing, the side chamber being in fluid communication with the first gas distribution duct via a first gas inlet, the gas intake being further disposed and configured to receive gas drawn from the product path area and to vent gas to a gas blower disposed in the side chamber and operatively coupled to the gas intake, the gas blower being further disposed and configured to draw gas from the product path area through the gas intake and to blow at least a portion of drawn-in gas into the side chamber and through the first gas inlet into the first gas distribution duct and through the plurality of slots to the product path area.

2. The chamber of claim 1 wherein each slot includes a width of from about 2 mm to about 8 mm, and preferably about 4 mm.

3. The chamber of claim 2 wherein each slot includes a substantially concave V-shaped cross-section.

4. The chamber of claim 2 wherein each slot includes a substantially Y-shaped cross-section.

5. The chamber of claim 1 wherein each slot allows gas to impact a top surface of the conveyor at a velocity pressure of from about 0.2 in/wc to about 0.4 in/wc at a clearance of about 100 mm from each slot.

6. The chamber of claim 1 wherein the housing includes a length from about 1000 mm to about 2000 mm, and preferably about 1500 mm, a width from about 900 mm to about 1200 mm, and preferably about 1000 mm, and a height from about 350 mm to about 750 mm, and preferably about 500 mm.

7. The chamber of claim 1 wherein the gas intake has a height at least as high as the product path area, and a length at least as long as a length of the product path area.

8. The chamber of claim 1 wherein the gas blower is operable to produce gas into the product path area at a volume of about 1000 cfm to about 2500 cfm, and preferably 2000 cfm.

9. The chamber of claim 1 wherein the first drying zone includes a sufficient volume to hold about 10 cu.ft. of gas such that as the gas blower produces gas to the product path area at a volume of about 2000 cfm, gas circulates about 200 times per minute within the first drying zone.

10. The chamber of claim 1, wherein the first gas inlet includes a heating device disposed and configured to heat gas forced therethrough.

11. The chamber of claim 10 wherein the first drying zone further comprises at least one temperature sensing device connected to an external temperature controller wherein the temperature controller receives an input signal from the temperature sensing device and sends an output signal to control the heating device.

12. The chamber of claim 10 wherein the heating device is operable to heat air to a sufficient temperature to increase a temperature of printed circuit boards from about 100°

C. to about 135°

C., and preferably to just above about 100°

C.

13. The chamber of claim 1 wherein the conveyor conveys printed circuit boards through the chamber at a preferable rate of about 1500 mm/mm.

14. The chamber of claim 1 wherein the housing includes insulation disposed on exterior surfaces.

15. The chamber of claim 1 wherein gas includes air.

16. The chamber of claim 1, wherein each slot is configured to conform gas forced therethrough such that the gas vents to the product path area as a curtain of gas.

17. The chamber of claim 1, wherein each slot has a width of from about 2 mm to about 8 mm and is configured to vent gas at a velocity pressure of from about 0.2 in/wc to about 0.4 in/wc.

18. The chamber of claim 17 wherein the blower and the plurality of slots are configured to produce from about 1000 cfm to about 2500 cfm of gas to the product path area.

19. The chamber of claim 18 wherein the gas blower and the plurality of slots are configured to circulate gas through the first drying zone about 200 times per minute.

20. The chamber of claim 18 wherein the first drying zone further comprises:

(i) a second gas distribution duct defined by the lower wall portion and a second discharge plate, the second discharge plate spaced from and above the lower wall portion and having a length extending along at least a portion of the length of the lower wall portion and a width extending along at least a portion of the width of the lower wall portion, and

(ii) a plurality of slots defined in the second discharge plate and configured to allow gas within the second distribution duct to vent from the second gas distribution duct, each slot being defined in the second discharge plate in an orientation substantially perpendicular to the direction in which the conveyor conveys the printed circuit boards and other electronic assemblies.

21. A chamber for drying circuit boards and other electronic assemblies by convection heating comprising:

a housing defined by an upper wall portion and a lower wall portion, each wall portion having a length and a width, and a first side wall and a second side wall, each side wall connecting the upper wall portion to the lower wall portion; and

at least a first drying zone disposed in the housing, the first drying zone including;

(i) a first gas distribution duct defined by the upper wall portion and a first discharge plate, the first discharge plate spaced from and below the upper wall portion and having a length extending along at least a portion of the length of the upper wall portion and a width extending along at least a portion of the width of the upper wall portion, the first discharge plate defining a plurality of slots configured to vent gas from within the first distribution duct;

(ii) a second gas distribution duct defined by the lower wall portion and a second discharge plate, the second discharge plate spaced from and below the lower wall portion and having a length extending along at least a portion of the length of the lower wall portion and a width extending along at least a portion of the width of the lower wall portion, the second discharge plate, the second discharge plate defining a plurality of slots configured to vent gas from within the first distribution duct;

(iii) a conveyor disposed in a product path area defined between the first discharge plate and the second discharge, the conveyor being spaced from and below the first discharge plate and from and above the second discharge plate to convey circuit boards and electronic assemblies through the product path area from a first end to a second end of the housing; and

(iv) a gas intake means disposed in a side chamber, at least a portion of the gas intake means being adjacent and facing the conveyor and extending along at least a portion of the first drying zone, the side chamber being defined between the first side wall of the housing and the gas intake and extending along an interior length of the housing, the side chamber being in fluid communication with the first gas distribution duct via a first gas inlet and the second gas distribution duct via a second gas inlet, the gas intake means being further disposed and configured to receive gas drawn from the product path area and to vent gas into the side chamber and to blow at least a portion of drawn-in gas through the first gas inlet into the first gas distribution duct and the second gas inlet into the second gas distribution duct and through the plurality of slots to the product path area.

22. The chamber of claim 21 wherein each of the first gas distribution duct and the second gas distribution duct includes a heater disposed and configured such that as drawn-in gas vents into the first and the second distribution ducts drawn-in gas is heated.

23. The chamber of claim 21 wherein each slot defines a width of from about 2 mm to about 8 mm, and preferably about 4 mm.

24. The chamber of claim 21 wherein the gas intake means is configured and arranged to vent gas into the product path area at a volume of about 1000 cfm to about 2500 cfm, and preferably 2000 cfm.

25. The chamber of claim 21 wherein the first drying zone defines an interior volume to contain about 10 cu.ft. of gas such that the gas intake means produces gas to the product path area at a volume of about 2000 cfm and circulates gas within the first drying zone at about 200 times per minute.

26. The chamber of claim 25 wherein each slot is spaced from a surface of the conveyor at a distance of about 100 mm and is further configured to allow gas to vent to the surface of the conveyor at a velocity pressure of from about 0.2 in/wc to about 0.4 in/wc.

27. The chamber of claim 21 wherein each slot defines a cross-section having one of a concave V shape and a Y shape.