Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1991-07-09
1993-06-29
Bennet, Henry A.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34 73, 34 15, 34 66, F26B 700
Patent
active
052223078
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a drying method for removing free water from electronic parts such as printed wiring boards, optical parts such as lenses and prisms, and precision instrument parts such as gears and lead frames having been subjected to advanced cleaning, surface treatments, etc. and to an apparatus therefor.
BACKGROUND
It is required in the drying of electronic parts such as semiconductors, liquid-crystal display devices and printed wiring boards, optical parts such as lenses and prisms, and precision instrument parts such as gears and lead frames having been subjected to advanced cleaning, surface treatments, etc. to give a high level of finish of drying inexpensively as well as to remove the free water residing on the surface of these parts, with safety and in a short time.
While a suitable drying method is generally selected taking the level of finish of drying to be expected for the object to be dried, efficiency of drying operation and cost into consideration, no drying method conventionally used, as shown below, can satisfy all of these requirements and development of a novel drying method has been expected.
(1) Wiping
In the wiping method, the free water is removed by wiping the wet surface with a piece of cloth or sponge. Although this drying method is simple and easy, it is difficult to apply it to small and complicated parts, and further the level of finish of drying is not good enough coupled with poor workability.
(2) Circulated Hot-Air Drying
While the circulated hot-air drying, in which objects to be dried are placed in a chamber where a hot air is circulated, is widely employed because of the ease of handling, the circulated air should be absolutely free from dusts or oily component for the purpose of preventing secondary contamination of the objects to be dried since the objects to be dried are directly exposed to the hot air. However, it is actually impossible to remove such contaminants completely, so that a high level of finish of drying cannot be expected.
(3) Gas (Air or Nitrogen Gas) Blowing
In the drying method using air or nitrogen gas blowing the objects to be dried, a large amount of high-purity gas is required. This results in higher costs. Further, the portions of the objects which are not exposed to the flow of gas cannot be dried well, leading to nonuniform drying, disadvantageously.
(4) IR or FIR Irradiation
In the drying method using IR or FIR as a heat source for drying, a high level of finish of drying can be expected if the ambient (environment) is clean, but drying proceeds only slowly, and large and complicated shapes of objects to be dried are liable to undergo nonuniform drying.
(5) Vacuum Drying
In the vacuum drying, objects to be dried are placed in a chamber and the free water is removed by evaporation by reducing the internal pressure of the chamber using a vacuum pump and the like. However, since a great latent heat of vaporization is lost from the objects upon evaporation of the free water, the objects are cooled whereby to require a long time for the evaporation (drying) of the free water. Further, there is a fear of contamination of the objects to be dried with the oil using in the vacuum pump.
(6) Spin-Out Drying
In the spin-out dr the free water is spun off by the centrifugal force and the object can advantageously be dried in a very short time. However, the water flung off, frequently containing contaminant, drifts in the form of mist within the apparatus and redeposits or contaminates the dried objects, disadvantageously.
(7) Drying with Solvent Vapor
In this drying, objects to be dried are brought into contact with a vapor of a hydrophilic or solvent to replace the free water with the solvent. This method can give good finish of drying. However, as an inflammable solvent such as IPA (isopropyl alcohol) is generally used as the hydrophilic solvent, an explosion-proof structure for the prevention of taking fire or a fire-extinguishing equipment should be installed.
(8) Water Replacement Drying.
In the wa
REFERENCES:
patent: 787093 (1905-04-01), Gathmann
patent: 805367 (1905-11-01), Lapp
patent: 942150 (1909-12-01), Tiemann
patent: 3262212 (1966-07-01), Buhr
patent: 3762065 (1973-10-01), Wahlgren
patent: 3943002 (1976-03-01), Schenerle et al.
patent: 4841645 (1989-06-01), Bettcher et al.
Patents Abstracts of Japan, vol. 10, No. 170 (E-412) (2226) Jun. 17, 1986 & JP-A-61 023 324 (Hitachi Seisakusho K.K.) Jan. 31, 1986.
Oba Shota
Oba Yoichi
Bennet Henry A.
Gomada Denise L.
Interface Technical Laboratories Co., Ltd.
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