Is your inventory deteriorating?

Selecting the right component storage ensures inventory remains in tip top condition. Totech EU’s Jos Brehler, answers some common questions on device handling

Q) Do we dry or do we store?

A) The answer is: both. Most of the time, assemblers do not know how much moisture has been absorbed by their components or PCBs, so they must be returned to a known state. Using a drying cabinet can reset the floor-life clock to zero, without inducing oxidation and inter-metallic build up caused by high temperature baking. The drying cabinet combines less than 0.5 per cent relative humidity (RH) with low heat around 45 to 55°C to provide drying times that rival high temperature baking but without the dangers.

Depending upon the work in progress (WIP) flow, components and PCBs that are subjected extensively to open air before soldering will require a storage cabinet. A drying cabinet holds the average humidity, including regular door openings, to one per cent RH, while a storage cabinet maintains the average humidity below five per cent RH after the component has been dried.


Q) What about cabinet humidity and ESD safety?

A) Static discharge is higher in the winter than in the summer because air is drier in the winter and the same is true for dry cabinets. The lower the humidity, the more concern you must have for ESD and all cabinets should be tested to meet ESD standards both inside and outside the glass.


Q) Do we need N2?

A) The Super Dry storage system from Totech EU achieves an atmosphere of less than 0.5 per cent RH at room temperature and produces a moisture vacuum at a water steam level of less than 0.05g/m³. This leads to a strong revertive drying process, whereby assimilated moisture is released out to atmosphere. Components are neither thermally stressed nor exposed to the danger of oxidation or inter-metallic growth.


Q) Why use heat inside cabinets?

A) The process can be thermally enhanced to accelerate drying times. To avoid oxidation problems, it is absolutely necessary that this process takes place in a moisture vacuum. Under these conditions the air moisture, which acts as an electrolyte, is not present and thus no oxidation can take place. In many cases traditional baking can become excessive and damaging at high temperatures, so with the XSD-Series, Totech responds to market demand for a reliable, effective drying system that can be easily integrated into the production process.

The XSD-Series is designed for maximum energy efficiency and delivers homogenic temperature throughout the interior of its double wall insulated enclosure. This can be used as per IPC regulations to temper sensitive components at 40°C, to dry reels or tubes at 50°C or printed circuit boards at 60°C. Thorough air circulation inside eliminates the need for repeated shrink-wrapping of devices in tape, which saves not only cost and time, but also protects the components themselves.


Q) What about oxidation and wet-ability problems?

A) If the temperature remains below 40°C, there will be no increase of oxidation because the O2 molecule only starts to react from 40°C. Many manufacturers wish to accelerate their drying time however, and therefore compromise by going up to 60°C.


Q) Do Super Dry cabinets fulfil IPC/JEDEC J-Std-033C?

A) These standards stipulate less than five per cent RH and state that the setting has to recover within the hour. Super Dry cabinets exceed this and are able to achieve 0.5 per cent RH and recover within four minutes. In fact, Super Dry product development has occurred faster than the standards have been revised and updated.

Totech believes that European companies are further advanced with lead free than their counterparts in the USA and EU customers should therefore encourage the IPC to revise its standards faster, in keeping with the technologies that have been implemented. For instance, the standards still suggest baking at 125°C, which most European assemblers avoid.


Q) What are the advantages of fast drying cabinets over baking ovens?

A) Fast drying cabinets require a fast recovery time after opening the door. Conditions should be back to set point in four minutes. Only then can you get an average of one per cent RH, including 10 or more door openings. Low RH in combination with 60°C heat will be nearly as fast as drying at 125°C, but without oxidation problems. Components do not need to be removed from reels or trays for this drying process because there is not enough heat to damage the

Q) What is recovery time and why is it important?

A) Recovery time is the ability to return to set point after the cabinet door is opened. As specified in our ‘reference conditions for drying’ document, Totech uses a calculation model to work this out. If the cabinet is unable to achieve one per cent, 60°C on an average throughout the day, we cannot give our customers this model to use for their drying process. For instance, that means that with a setting of 0.5 per cent, the Totech cabinet can achieve 0.2 per cent. If the doors are being opened five times in a morning, the average must still be maintained at one per cent, not five per cent, or more. This can only be achieved with a very low RH in combination with fast recovery times.


Q) Do all dry storage cabinets offer the same performance?

A) Totech believes the answer is no. Some suppliers claim to achieve one per cent RH but in practical terms, this is not maintained. For instance, this figure can only be achieved when the doors remain closed for many hours, or are opened once every few hours. We know from experience that manufacturers typically need to access their cabinets more frequently than that.


Q) Does component thickness affect drying time?

A) Simply stated, the thicker and heavier the component, the longer it will take to absorb moisture to a critical level and the longer it will take to get the moisture out. The smaller and lighter the components, the faster the absorption and the faster it can be dried. Some components are saturated within two hours after being totally dried. The critical level for moisture is 0.10wt per cent. Our reference conditions for drying documents lists components and their respective MSL.