1. Glass Desiccators
Desiccators in cleanrooms are usually glass jars used to store pre-dried samples of hygroscopic chemical reagent. They’re sometimes also used to cool substances that were heated in a beaker. In a laboratory, they are very useful, but in a cleanroom, they can be a contamination hazard.
One of the primary issues with glass desiccators is that cleanrooms usually require very precise humidity controls. The devices manufactured in semiconductor, medical device, and pharmaceutical cleanrooms are moisture-sensitive devices (MSDs). The desiccators cannot maintain these extremely low levels of relative humidity.
Desiccators create a drying effect through adsorption using a desiccant powder like calcium chloride or silica gel on the bottom. The sample sits on a small platform, and the jar is sealed using silicone grease. Once this system reaches its saturation point, it can’t provide moisture protection. Saturation is visible when the powder changes color from blue to pink. To return to its adsorptive abilities, the desiccant has to be regenerated through a 24-hour heating cycle to bake out the moisture.
At this point, the desiccator has to be manually handled. This is both disruptive to processing and poses a risk of contamination. In any case, these jars generally provide insufficient drying.
The vacuum desiccators will effectively dry samples that can withstand the vacuum environment. However, the entire system brings noise and contaminants to a cleanroom.
2. Desiccant-based Dry Cabinets
What are your options for using desiccators in a controlled environment like a cleanroom?
Dry cabinets alternate between two desiccant modules that cycle in and out of the airflow unit. One provides moisture adsorption and the other undergoes regeneration through an integral heating module fan. In this way, the cabinet offers better storage capacity at a controlled RH level.
This kind of system is perfect for long-term bulk storage of microelectronic components, moisture-sensitive optical devices, and other similar applications. The cabinets eliminate the need for manually removing and restoring saturated desiccant. The products are easily accessible, thereby not obstructing the process. The even set point control and low relative humidity monitoring offer benefits to this kind of system over the static, or glass jar system. However, the dry cabinet is more complex and expensive to own and operate.
For the most stringent cleanroom environments, the dry cabinet still poses some issues. Fans are used in these systems, which can cause particles to enter the airflow. HEPA filters can be added to capture the contaminants, but they also add an additional moisture load, which can compromise drying efficacy. The fans can also cause turbulence outside of the cabinet, disrupting the essential laminar airflow.
3. Variable-purge System
When traditional desiccators aren’t clean enough to use in your controlled environment, what are your options?
For a cleaner alternative than the two previously mentioned, dry nitrogen gas is the best desiccating medium. Without contributing particles, a nitrogen-purged system provides superior RH control with automated set points far below 5% RH. It maintains an inert environment for anything that is sensitive to humidity or other chemical vapors.
The variable-purge system uses highly precise RH sensors and effective airflow engineering to minimize humidity recovery times while conserving nitrogen. All things considered, these systems are the most cost-effective for any product that will experience high defect rates with even a little exposure to moisture in the air.
Do you need cleanroom certification or validation? Looking to build a modular cleanroom? Our experienced staff at Gerbig Cleanrooms has 30 years of expertise that you can depend on. Call us at 888-628-0056 or email firstname.lastname@example.org.