After hurricanes Katrina and Rita, many electronics manufacturers and suppliers with facilities in Louisiana, Texas, Mississippi, and Alabama had their work cut out for them. Many factories and warehouses were devastated by flood and wind damage. One might conclude that those inventories were lost and written off as losses to be replaced by insurance companies. But what became of the legacy electronics systems with components, boards, and layout drawings that are nearly irreplaceable? Manufacturers are now attempting to salvage these electronics assemblies. The ability to salvage these critical systems not only benefits the product owners but also impacts the U.S. and global economies, particularly in systems that are used to supply fuel, energy, communications, water, and food. The EMPF is assisting the recovery of such assemblies by providing a cleaning process for boards and assemblies exposed to the high humidity and storm damage of the harsh hurricane environments.

Recovery of economically or strategically important electronic hardware requires a stepwise approach:

1. Evaluation – A high-level decision which looks at the pros and cons of recovery vs. replacement.
2. Analysis of damage – Assess observable and potential damage: e.g., water logging, contamination, corrosion (using visual examination), chemical and physical analysis.
3. Damage mitigation approach – propose different methods to remove or eliminate damage.
4. Process of mitigation – for example, cleaning the circuit boards and drying.
5. Post-mitigation testing and documentation.

Hurricane exposure encompasses everything from extended high humidity to submersion in seawater. The exposure comes directly from damages to the storage and manufacturing facilities. Damage reports vary in severity from power loss and air conditioning failure (high-humidity) to structure failure (exposure to the salt atmosphere from hurricane environments) to tidal flooding (submersion in brine solution).

During the recent hurricanes, four feet of tidal floodwaters engulfed the facilities and much of the stock of electronic circuit boards. These floodwaters carried with them various forms of foreign matter that included sewage, oil, various forms of salts, and bacteria (Figure 2-1). Exposure to these elements results in board failures caused by corrosion and short circuits. Salt residue and unidentified contaminates, both visible and undetectable, coat the affected boards and components. To restore these boards to useful (though sometimes limited) operating condition, these assemblies must be cleaned of the harmful contaminates. Contaminates can be grouped into two categories – ionic and nonionic. The two most common failures due to ionic contamination are corrosion and dendrite growth. Both of these conditions can cause device failure. The most common sources of ionic contamination are flux, cleaning fluids (e.g., tap water), and plating chemistry residue (from the surface finish). In the case of the boards which the EMPF inspected, salt water posed the largest threat to the reliability of the assemblies. Ionic contamination can also result in dendrite growth, which in turn leads to short circuits.

Non-ionic contamination is not usually of great concern to most electronic device manufacturers, but this does not mean that it does not affect reliability. The most common failure modes due to non-ionic contamination are reduced solderability, lack of connectivity, and sensor malfunction. Since non-ionic contaminates are nonconductive, they can disrupt the flow of electricity through these connectors if they are present on an edge card connector or inside a socket.

The EMPF has observed several problems with insulating films present on gold edge connectors. The good news is that most of the contaminates are soluble in water, and with the aid of surfactants, they can be removed with a well executed cleaning process. Such a process must be well thought out and kept under extremely tight controls. Before the affected boards and components are cleaned, a recovery plan is implemented. EMPF engineers meet with the board designers, quality assurance personnel, and manufacturing engineers, to discuss the details of the operation. An outline is formed with the steps required to conduct the cleaning and recovery operations based upon some critical considerations.

Severity of the exposure
The history of each board’s storage and exposure conditions is evaluated. This includes an original date of manufacture, time in storage, storage location (e.g., in crates at the floor level, shelved above the water line, etc.), and any processing or recovery operations performed after exposure to extreme environments.

Product needs assessment
Each board set is prioritized by the end-use application (in some cases, the individual needs of specific facilities are considered) and availability of replacements. Systems that are more important to the individual facilities are evaluated first. These are the systems that are directly responsible for providing necessities like water, food, and fuel.

Cleaning process
The cleaning process is created using standard electronics manufacturing in-line cleaning equipment and materials as a base (Figure 2-2). Additional processes and materials are added to ensure removal of any atypical foreign matter to which the assemblies may have been exposed. Drying and baking time are also under consideration. Current guidelines for component and assembly drying and baking after cleaning and storage are targeted for surface mount packages designed and built within the past 15 years. They address moisture sensitive components that absorb water vapor from uncontrolled and controlled atmospheres. Because legacy electronics have been developed using older technology (1980s and earlier), compatibility issues exist with high temperature baking, even in short duration. For example, some older dip packages are rated for operation at a maximum temperature of 60ºC. IPC J-STD-033 recommends baking some moisture sensitive surface mount components at 125ºC for up to 16 hours. Blindly following industry standards that are recommended for current technology would surely lead to component failure in the case of many older systems.

Development of a testing/validation system
Visual inspection and ionic cleanliness testing are used as a base for evaluating the effectiveness of the cleaning and drying operations. Although IPC J-STD-001 and IPC-A-610-D provide specifications for ionic cleanliness and visual inspection criteria, the age of the board and any add-on materials (markers, labels, etc.) will influence the results, possibly producing false readings. For example, the adhesive used for stick-on labels contains ionic residues that will give a false contamination reading. Careful scrutiny of inspection and cleanliness testing results is required. Based upon these factors, multiple recovery plans were developed at the EMPF. The following is an example of a cleaning process developed to clean boards that have a mild level of exposure and have components which are compatible to an in-line hot water cleaning process. The performance of the components on these boards would not be affected by baking.

Example cleaning process for boards with mild level exposure and limited component sensitivity:

Receiving
Board lots are recorded; old storage bags and desiccants are disposed.

Compatibility assessment
Boards are inspected to ensure compatibility with the proposed cleaning process. This includes evaluating temperature ratings, moisture sensitivity, and board density.

Pre-wash
Particulate matter is removed by manually scrubbing theboard with a coarse brush, using a deionized water and Kyzen Cybersolve solution.

Cleaning
Technical Devices NuClean PolySMT 318XL in-line aqueous cleaner is used for its efficiency and effectiveness. Extremely clean (17.5 Mega-ohm) deionized (DI) water is supplied to the cleaner. The DI supply water is heated to 130ºF. The assemblies are put through the cleaner with a conveyer speed of 2 feet per minute. Kyzen Aquanox A4520 cleaning fluid is used in the wash stages of the cleaning cycle. This cleaning agent is safe for use on yellow metals, aluminum, ferrous metals, composites, and various plastic materials (including Teflon and PVDF).

Inspection/validation
100% visual inspection for cleanliness is performed per IPC-A-610-D class 3 inspection criteria. Resistivity of Solvent Extract (ROSE) testing (Bulk Ionics) is also performed in accordance with IPC J-STD-001. Assemblies pass the cleanliness inspection when they contain less than 1.56 micro grams/cm2 of sodium chloride equivalent, unless otherwise noted. This specification applies mainly to assemblies. Components, connectors, wire harnesses, etc., are not required to meet this specification.

Drying/baking
Baking is performed in an air circulating oven or other thermal chamber at 60ºC for eight hours.

Shipping
Board lots are marked as “cleaned” and placed into new static resistant packaging with a desiccant to prevent  moisture absorption.

The results have shown that execution of these cleaning processes can produce an effective revival for boards that would surely be rendered inoperable otherwise. The key to this successful effort has been well thought out planning, quick response, an efficient cleaning process, and the ability to validate board cleanliness.