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Storage of Moisture Sensitive Devices (MSDs)

 

There are two important aspect with storage of MSD, namely, dry storage and ESD safe.

 

1. MSD Dry Storage

 

Generally, after MSDs are taken off from chip mounter and they will be stored in dry condition, such as Totech dry cabinet before next procedure. And many staff on production line think that the floor life will stop counting after they are put into dry condition; however, this is only true if the MSDs were kept dry before. And the fact is that once the MSDs are exposed for a long time (>1 hour), the absorbed moisture will stay in the encapsulation of the components and permeate into inner part to cause damages.

 

Researches show that after SMDs are taken out from MBB, its floor life will keep a function relationship with ambient environment, so the safer handling is to control MSDs strictly as per the requirements of J-STD-020 and J-STD-033. And if the MSDs were not affected with damp and the exposure time is very short after unpacking (< 30 minutes) under 30 /60%, then it is OK to keep storing the components with dry cabinets or MBBs.

 

If MBBs are adopted, the desiccant can still be used if the exposure time does not exceed 30 minutes. For MSDs with MSLs 2, 2a, 3, if the exposure time is within 12 hours, then the drying time is 5x exposure time in a dry cabinet with humidity <10%RH, and for MSDs with MSLs 2, 2a and 3, if the exposure time does not exceed floor life, the period when components are kept in 10%RH dry cabinet should not be counted in exposure time. For MSDs with MSLs 4,5,5a, if the exposure time is within 8 hours, then the drying time is 10x exposure time in a dry cabinet with humidity <5%RH. And exposure time can be counted from 0 after drying storage. And dry storage in 5%RH dry cabinet is equivalent with the storage in undamaged MBBs with unlimited floor life.

 

Totech Super Dry cabinets SDU series control humidity 0.5%RH, and suitable for MSDs with all MSLs both at workshop and warehouse.

 

2. ESD safe.

 

ESD is a tiny version of lightning. As the current dissipates through an object, it's seeking a low impedance path to ground to equalize potentials. In most cases, ESD currents will travel to ground via the metal chassis frame of a device. However, it's well known that current will travel on every available path. In some cases, one path may be between the PN junctions on integrated circuits to reach ground. This current flow will burn holes visible to the naked eye in an integrated circuit, with evidence of heat damage to the surrounding area. One ESD event will not disrupt equipment operation. However, repeated events will degrade equipment's internal components over time.

 

Totech Super Dry is with perfect ESD safe design to make sure safe storage.

1)      The cabinet body is with ESD safe coating with even surface resistance and keep permanent ESD safe function (not ESD safe paint).

 

2)      Both outside and inside cabinet body are with gray coating and it is dissipative type with 10^6Ω/, ESD safe glass windows both outside and inside with 10^8 Ω/, the shelves are made of stainless steel or ESD safe coating steel with 10^6 Ω/ and 1MΩ grounding wire, well comply with ESD safe requirement in IEC 61340-5-1.

 

3)  All Totech Super Dry are with gray ESD coating, not black.

The ESD surface resistance is with two types, conductive type (10^4surface resistance <10^6 ) and dissipative type (10^6~10^9). And the conductive type is generally with black color which is mixed by carbon powder, while dissipative type is mixed by metal powder with brighter color and it is suitable for inner coating for dry cabinets to putting and taking components.

 

  Conductive type is with lower cost and the static electricity is discharged faster, while the dissipative type can control the discharging time, suitable for eliminating the static electricity for semi-conductors.

  

  Besides, the conductive type may affect the environment as it contains carbon if it falls into the environment, and it is not advised especially for clean room, while the dissipative type caused no micro pollution to the environment.

 

 


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