Drying and gas or vapor contact with solids – Process – With nondrying treating of material
Reexamination Certificate
2000-10-26
2003-09-23
Lazarus, Ira S. (Department: 3749)
Drying and gas or vapor contact with solids
Process
With nondrying treating of material
C034S218000
Reexamination Certificate
active
06622399
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of electronic packaging and storage of electrical components, and more particularly, the invention relates to a system and method for reducing moisture in stored electrical components by maintaining a warm and dry atmosphere in a component storage area.
2. Brief Description of the Related Art
Plastic cases for electronic active components or integrated circuits are gaining in popularity over ceramic or metallic packages as they are easier to work with and less expensive. They have, however, the disadvantage of being sensitive to moisture. Moisture from atmospheric humidity is absorbed by the package via permeation. If the moisture level inside the package reaches a critical point, the device may be damaged when brought up to temperature during the reflow soldering process. These types of moisture-induced failures are referred to as the popcorning effect due to the audible popping when a crack appears in the package from moisture overpressure. If cracking occurs, air and moisture may contact the silicon die inside the package resulting in corrosion. The reliability of the product is seriously jeopardized if an integrated circuit package cracks during reflow. Micro-cracking is also hard to detect. Therefore, it is critical for printed circuit board assemblers to avoid moisture induced failures and popcorning defects and to limit the exposure of components to moisture.
There are currently no specific solutions to prevent the absorption of moisture. Assemblers normally adopt a “moisture management system” in order to control the moisture exposure levels. A part of such a system involves re-bagging the components in dry and desiccant bags after an initial usage. Another part of the current practice is to monitor floor life of a component or the time that the component is exposed to atmospheric moisture. After a floor life has expired, the moisture in the package may be reduced by performing a process referred to as “baking” during which the component is heated to remove moisture.
The limit level or critical moisture level (level at which cracking will occur) for a package depends on the package itself and the temperature at which it will be exposed during the assembly/soldering process. A higher reflow temperature results in a lower critical moisture level. The determination of the weight gain percent failure level is therefore component specific and process specific.
While baking prevents the moisture induced failure and the popcorning effect, it is time consuming and may be difficult to manage. For example, products qualifying with a moisture sensitivity corresponding to the IPC/JEDEC J-STD-020 standard are normally baked at an elevated temperature for a period varying from 24 hours (baked at 125° C.) to a week or more (baked at 40° C.). Sometimes this baking process is shortened or interrupted by the assembler because the components are urgently required to finish a production load that is back ordered. Baking also oxidizes the components and ages them by growing the intermetallic layer of the component joint structure.
As the reflow soldering temperatures are expected to increase when lead-free alloys are introduced on the market (217° C. and higher melting points for lead-free alloys versus a 183° C. melting point for standard lead alloys) moisture control will become even more critical in the future.
Dry storage cabinets are available which prevent moisture absorption. However, these dry storage cabinets have not been used to demoisturize components and eliminate the need for baking.
Accordingly, it would be desirable to provide a system which prevents moisture absorption and also removes moisture from components without baking.
SUMMARY OF THE INVENTION
The present invention relates to the use of a warm and dry atmosphere in a component storage area. The warm and dry atmosphere in the storage area provides the benefit of eliminating the baking process and other moisture management issues.
In accordance with one aspect of the present invention, a component storage system includes an enclosed component storage area, a dry gas delivery system for delivery of a dry gas to the storage area to maintain a dry atmosphere in the storage area and to prevent moisture from being absorbed by the components, and a temperature control system for controlling a temperature of the dry gas to about 10° C. to about 60° C.
In accordance with an additional aspect of the present invention, a method eliminating moisture from electronic components includes the steps of storing electronic components in a storage area, and maintaining a warm and dry atmosphere in the storage area by enclosing the storage area and injecting a warm and dry gas into the storage area at a flow rate and temperature which are controlled to eliminate moisture from the components in the storage area.
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Boyce Kristen
Rabia Stephane
Theriault Martin
l'Air Liquide-Societe Anonyme a' Directoire et Conseil
Lazarus Ira S.
Ragonese Andrea M.
Russell Linda K.
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