Restoring electronic hardware damaged from harsh conditions of environmental exposure is a difficult task.

Recently, the EMPF’s facilities were instrumental in the recovery of several thousand circuit boards damaged following hurricane Katrina.

The following three step process outlines the EMPF development of a cleaning procedure which was effective at restoring these assemblies:

1. Understand what you are trying to remove.
2. Determine the limitations of the assembly
3. How densely populated is the assembly?

1. Understand what you are trying to remove.
The floodwaters, which these assemblies were subjected to, contained a broad spectrum of contaminants including unknown solvents, hard water residues, salt, dirt and oil. The degree of contamination, coupled with the myriad of contaminants, demanded an effective, repeatable procedure to achieve pristine levels of cleanliness.

Cleaning chemistries have changed since the Montreal Protocol banned halogenated hydrocarbons. Those early chemistries worked very well for the flux residues of the day (activated rosin) by dissolving and washing them off the surface through direct immersion, spraying or vapor degreasing. The number of options available today is less, with water as the "universal solvent".

Because of the limited solubility of many materials in water, the key to removal is a combination of time, water volume, temperature, and efficiency of agitation. Ultimately, water alone may not suffice, thus additives (surfactants) will be introduced to reduce surface tension, improve penetration, and induce one or more of the following phenomena: wetting, emulsification, solubilization, saponification, deflocculation, and sequestration.

For this endeavor, the water-soluble and semi-soluble residues required de-ionized water while the oil, grease and dirt required saponifier chemistry.

2. Determine the limitations of the assembly.
In the case of most assemblies there will be parts (ICs, any ceramic components, capacitors, etc.) that should not be subjected to vibration which will preclude ultrasonic pre or post cleaning. In this particular case there were some assemblies with significant debris that required some pre-cleaning. Temperature was a factor for some of the older assemblies, as IPC J-STD-033 recommends baking some moisture sensitive surface mount components at 125ºC, while some older dip packages are rated for baking at a maximum temperature of 60ºC. Obviously care needs to be taken in this regard, as using current recommendations on this older technology would most likely have lead to component failure.

3. How densely populated is the assembly?
The edge connectors on some of the assemblies will tend to collect material along with the Duaal In-line Packages (DIPs) and Small Outline Integrated Circuits (SOICs). The more densely populated the board, the more areas there are going to be for particulate mater to collect

The obvious objective was to remove the dirt and debris. The end use for these assemblies required a level of cleanliness that assured long term reliability. As a result, the level of ionic contamination also needed to be determined. Given the number of assemblies involved, a combination of IPC-A-610D visual inspection and J-STD-001 bulk ionic testing, using an Alpha Metals 500M SMD II Ionograph, was performed for process control and to provide confirmation of cleanliness.

Based on an understanding of the conditions and requirements of the material at hand, the following steps were taken.

1. Part removal, rework steps, as needed.

2. Pre-cleaning with a brush in Kyzen Cybersolve® SB8501, deionized water solution as needed.

3. All cleaning was performed at ACI by using a Technical Devices NuClean® PolySMT 318XL in-line aqueous cleaner, operating condition:

• Kyzen Aquanox® A4520/deionized water (17 Mega-Ohms) solution (17%v/v)
  
• Rinse and wash temp: 130°F
• Belt speed: 2.0 ft/min.
• Air dryer temp: 170°F

4. Inspection and cleanliness testing.

5. Drying the assemblies at 60°C for eight hours.

This process significantly improved the cleanliness of the assemblies and reduced the ionic residue levels, some of which were above 50 micrograms of NaCl equivalents/square inch down to less than 2 micrograms of NaCl equivalents/square inch, which is well beyond the J-STD-001 requirement of 10.06 micrograms of NaCl equivalents/square inch maximum.