Air knife drying system

Details Air knife drying system Air knife drying system

1999-02-19

2001-07-17

Moore, Chris K. (Department: 1744)

Brushing, scrubbing, and general cleaning

Machines

With air blast or suction

C015S316100, C015S346000

Reexamination Certificate

active

06260231

ABSTRACT:

FIELD OF THE INVENTION
The present invention provides a drying system for use with a liquid cleaning apparatus designed to clean and dry workpieces, such as printed circuit boards and the like. More specifically, embodiments of the present invention are directed to a drying system and method to remove water and liquid cleaner residues from printed circuit boards.
BACKGROUND OF THE INVENTION
Various types of liquid cleaning systems are used to clean printed circuit boards for removal of contaminates, such as flux residues, resins and the like, which remain on printed circuit boards emerging from the soldering process. Liquid cleaning systems, such as that disclosed in U.S. Pat. No. 5,113,882, incorporated herein by reference, typically include a series of processing chambers, each dedicated to a specific phase of the cleaning process, through which printed circuit boards pass. As shown in
FIG. 1
, printed circuit boards enter a liquid cleaning system on a conveyor chain or belt
10
and move through each cleaning chamber including a washing tank
22
, hot water sprays
30
, a second washing tank
32
, and a drying chamber
38
from which printed circuit boards exit the cleaning system. Liquid cleaners used in such liquid cleaning systems include saponified cleaning agents and terpene-based solvents which have low flash points and are potentially flammable and explosive when sprayed in air. In addition, such liquid cleaning agents and solvents are highly volatile and produce unpleasant odors when released in air. For this reason, many liquid cleaning systems, such as shown in
FIG. 1
, are enclosed systems in which vapors and liquid particles produced from use of such cleaning agents and solvents are contained within the liquid cleaning systems by various means of condensation and air recirculation. Other liquid cleaning systems purge inert gas, such as N
2
, into the atmosphere of the cleaning chambers to displace air and minimize the potential for ignition or explosion, as well as to form liquid seals at the entrance and exit openings and between cleaning chambers.
Despite such methods, cleaning agent vapors are released into the air outside of the liquid cleaning system by evaporation of water particles and cleaning agent residues that are not removed in the drying chamber
38
and remain on printed circuit boards exiting the liquid cleaning system. The drying chamber
38
is typically the last phase of the cleaning process in which water particles and cleaning agent residues can be removed from clean printed circuit boards. It is, therefore, advantageous to substantially dry printed circuit boards within the liquid cleaning system before printed circuit boards are exposed to the external environment. It is also advantageous to remove cleaning agent residues from printed circuit boards as such residues can cause short circuits during performance tests of printed circuit boards and during the operation of printed circuit boards.
As shown in
FIG. 1
, prior art drying systems include the drying chamber
38
in which water and cleaning agent residues are removed from printed circuit boards by blowing steam and/or air onto the surfaces of printed surface boards. The drying chamber
38
is equipped with air diffusers
60
positioned above and below the conveyer belt
10
to provide a uniform flow of air onto both the top and bottom surfaces of the printed circuit boards. The dryer chamber
38
is also equipped with heaters
62
to warm air and deflectors
64
to direct air flow. Another embodiment of prior art dryers is shown in FIG.
2
and includes directional nozzle dryers
201
positioned above and below the conveyor belt
10
. The nozzle dryers include flexible metal tubing
202
, capable of adjustment to direct air flow, and nozzle heads of various designs, such as flare and fan nozzle heads
203
. Other prior art drying systems utilize air knife dryers to deliver compressed air to the surfaces of printed circuit boards.
Prior art dryers such as those described above, are typically positioned above and below printed circuit boards as the circuit boards are conveyed through the drying chamber. Prior art dryers primarily function to dry only the top and bottom surfaces of printed circuit boards and are not capable of directing sufficient steam and/or air to remove water and cleaning agent residues from the sides of printed circuit boards nor any electrical components mounted thereon. Prior art drying systems typically used in liquid cleaning systems do not provide for side drying.
Prior art dryers use typically steam and/or normal, heated or pressurized air as drying agents to forcibly remove water and residual cleaning agents from printed circuit boards. Air knife dryers are used particularly to concentrate and deliver pressurized air onto the surfaces of printed circuit boards, forcibly removing remaining water particles and cleaning agent residues.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide a system and method for drying printed circuit boards and the like in a liquid cleaning system that produces substantially drier printed circuit boards than prior art drying systems and achieves greater economy in the use of air as a drying agent.
In one general aspect, the invention provides a system and method for drying printed circuit boards in a liquid cleaning apparatus which includes a series of air knife dryers enclosed within two drying modules. The first drying module houses a first set of top and bottom air knife dryers which includes at least one top air knife dryer, positioned above a conveyor belt carrying printed circuit boards through the liquid cleaning apparatus, and at least one bottom air knife dryer, positioned below the conveyor belt. The air knife dryers are preferably symmetrically opposed and aligned above and below the conveyor belt. It is also preferable that the first set of top and bottom air knife dryers include an additional top air knife dryer located above the conveyer belt. The printed circuit boards pass between the top and bottom air knife dryers which deliver pressurized air in a substantially perpendicular flow directly onto both the top and bottom surfaces of the printed circuit boards as desired thereby forcibly removing water particles and cleaning agent residues. Printed circuit boards pass under the second top air knife dryer which, like the first set of top and bottom air knife dryers
110
, similarly delivers air in a substantial perpendicular flow onto the top surfaces of the printed boards and removes water particles and cleaning agent residues thereon.
After passing under the second top air knife dryer, the printed circuit boards continue through the first drying module and pass at least one side air knife dryer, and preferably two side air knife dryers positioned adjacent to the conveyor belt and downstream from the first set of top and bottom air knife dryers. The side air knife dryers are preferably symmetrically opposed and aligned on either side of the conveyor belt. The side air knife dryers may be similar to the first set of top and bottom air knife dryers. As the printed circuit boards pass between the side air knife dryers, pressurized air is delivered in a substantially parallel flow directly onto the sides of printed circuit boards as desired, forcibly removing water particles and cleaning agent residues from the sides of printed circuit boards and any electrical components mounted thereon, as well as metal and other electrical edge contacts common to printed circuit boards. Printed circuit boards continue to pass through the first drying module and enter a second drying module.
The second drying module is positioned downstream from the first drying module and houses a second set of top and bottom air knife dryers which may be similar to the first set of air knife dryers. The second set of top and bottom air knife dryers includes at least one top air knife dryer and at least one bottom air knife dryer positioned above and below the conveyor belt and preferably symmetrically opposed and aligned. An add

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