- Do we need to Dry or do we need to Store?
We need both. Most of the time assemblers do not know how much moisture has been absorbed by their components or PCB’s, so they must be returned to a known state. A drying cabinet can reset the floor life clock back to Zero without inducing oxidation and inter-metallic growth caused by high temperature baking. The drying cabinet combines <0.5% RH with low heat (45-55C) to provide drying times that rival high temperature baking but without the dangers. (download “Reference Conditions for Drying”)
Depending upon WIP flow, if components and PCB’s are subjected extensively to open air before soldering, a storage cabinet is required. Whereas a drying cabinet must hold the average humidity, including regular door openings to 1%RH, a storage cabinet must maintain the average humidity (including regular door openings) below 5%RH to stop the floor life clock (IPC-JEDEC-Std-033C)
- What effect has the humidity inside of the cabinet in relation to ESD Safety?
It’s common knowledge static discharge is higher in the winter then in the summer; in the winter the air is drier than in the summer. So it is in dry cabinets; the lower the humidity, the more concern you must have for ESD. Hint: cabinets should be tested to meet ESD standards both inside as well as outside of the glass.
- Do we need N2 or can we leave nitrogen behind?
The Super Dry® storage systems of Totech EU achieve an atmosphere of < 0.5 % R.H at room temperature and produce a “moisture vacuum” with a water vapor level of less than 0.05 g/m³. This leads to a strong revertive drying process in the devices, in which assimilated moisture is released to atmosphere. This is very protective as components are neither thermally stressed nor exposed to the accelerators of oxidation or inter-metallic growth.
- Why use heat inside cabinets?
To accelerate the drying times, the revertive drying process described above can be thermally enhanced. To avoid oxidation problems, it is absolutely necessary that this process takes place in a “moisture vacuum”. Under these conditions the electrolyte (air moisture) is not present and thus no oxidation takes place. In many cases traditional baking becomes excessive and damaging at very high temperatures.
The XSD-Series is a highly energy efficient alternative and delivers even temperature throughout the interior of its double wall insulated enclosure. This technique can be put to use for 033C specified tempering of sensitive components at 40 °C as well for drying of reels or tubes at 50 °C or printed circuit boards at 60 °C.
- What about oxidation and wet-ability problems?
If the temperature remains below 40 C, there will be no increase of Oxidation; the O2 molecule starts to react from 40 C. However many manufacturers wish to accelerate their drying time and so compromise and go up to 60 C max.
- Do Super Dry® cabinets fulfill IPC/JEDEC J-Std-033C?
These standards refer to < 5% RH and that the setting has to come back within the hour; Super Dry cabinets exceed this and are able to achieve 0.5% RH and recover within 4 minutes. The standards do not adequately address average RH% conditions. Super Dry product development has occurred faster than the revisions and updating of the standards. IPC is a global organization. We all understand that European companies have longer experience with lead free then in North America, and lead free processing greatly accentuates the need to control moisture. OEMs and EMS providers should encourage the IPC to revise the standards faster, and in keeping with the technologies that have been developed and proven outside North America. For instance, the standards still suggest baking at 125C, which most European assemblers avoid due to oxidation, decreased wet ability and increased inter-metallic growth.
- Can we use fast drying cabinets instead of baking ovens? Are there advantages?
If we speak about fast drying then we need a very fast recovery time after opening the door; it should be back to set point in 4-5 minutes. Only then you can get a 1% RH on an average including normal access frequency. Low RH in combination with 60 C will be nearly as fast as drying under 125C….but without Oxidation problems. Components do not need to be removed from Reels or Trays for this drying process, because we do not use enough heat to damage the carriers.
- What is the meaning of recovery time and why is it significant for drying?
Recovery time is ability to return to set point after a door opening. If you look to our “Reference conditions for drying” it provides a calculation model. Low RH is critical to the low temperature and high speed. The average must maintain 1%… not 5% or more. This can only be achieved with powerful de-humidification and fast recovery times.
- Do all dry storage cabinets offer the same de-humidification performance?
Not all situations require the same; as discussed previously. For example, long term safe storage with infrequent access and accelerated drying require two very different minimum performance standards.