Semiconductor wafers and die are not inherently moisture sensitive. However, wire bond pads are quite sensitive and any presence of moisture may accelerate failure, such as bonding issues and delamination, which may only be discovered during product packaging. KGD (known good die) parts are typically shipped in tape and reels packaging which cannot be baked to remove moisture.

The best preventive measure is to maintain optimal controlled storage environments to prevent any failures. When in storage, die and wafers, should be stored die banks with a temperature between 18°C and 24°C and relative humidity of less than 30%.

1. Vacuum sealed packaging is not recommended for the long term and should be considered temporary transport packing to avoid moisture absorption and other contamination.

2.  Storing wafers and dies below <10%RH can result in a build-up of electrostatic fields, storing over <40%RH will result in condensation and moisture ingress.

3.  Typically, storage in a nitrogen cabinet is recommended, however, the long term cost with N2 storage is quite high.

4.  Desiccants could cause mechanical abrasion of particulates and the effectiveness may become harmful in the long term if excessive moisture is present.

Eureka Fast Super Dryer offers the same moisture & humidity-controlled storage options with fast recovery times without using costly nitrogen (N2) purging. However, if the customer has specific requirements N2 purging is available as an option.

IC Devices, Packages and Components

All semiconductor devices are susceptible to damage or degradation during storage and handling. Non-hermetic, plastic-encapsulated surface-mount devices are particularly sensitive to moisture-induced stress during printed wiring board assembly.

IPC/JEDEC J-STD-033 provides guidelines for various moistures sensitivity levels (MSL) and allowable exposure time to specific ambient temperature and moisture levels before baking is required.

1.  When opened packages or lots are used, the remaining devices should be resealed or placed in a dry box at no more than 10% RH within one hour of the bag opening.
2.  If the exposure to the ambient environment exceeds the allowable time, the devices must be baked before mounting. However, baking will cause oxidation and intermetallic growth causing solderability issues.

Eureka’s dry cabinet utilizes powerful multi-porous molecular sieve desiccants which will provide alternative drying methods to baking oven and reduce oxidation problems caused by heating cycles.

Printed Circuit Board Manufacturing
Circuit boards if not properly dried and stored, can contain significant amounts of moisture from processing. Any moisture, even in trace amounts, will lead to delamination and warping in PCB when high reflow temperatures cause the moisture inside the layers to expand.

Until the ‘IPC-1601 printed board handling and storage guidelines’ was published in 2010, PCBs were generally overlooked for storage and moisture protection for printed circuit boards.  Often times, PCBs are shipped in foil or an ESD bag instead of Moisture Barrier Bags (MBB). PCBs then arrive at the assembly floor with absorbed moisture requiring baking. IPC-1601 states that if “printed boards have absorbed excessive moisture, baking is the most practical remedy.” However, baking increases cost and cycle time and can also degrade solderability of the printed board. “In general, both the printed board fabricator and the user should strive to avoid baking by practicing effective handling, packaging, storage, and process controls…”

Baking also accelerates solid diffusion between metals and increases intermetallic growth which leads to a “weak knee” or other solderability issues if the intermetallic layer reaches the surface and oxidizes.

ENIG, immersion tin, silver, and OSP are finishes often used on printed circuit boards because they are lead-free. However, these materials are susceptible to oxidation and corrosion from exposure to moisture and humidity. This oxidation causes dewetting after soldering, which can lead to poor joints at assembly and ultimately lead to failure of the board.

Boards with these types of finishes should be stored in environments controlled between 68°F – 82°F (20°C – 25°C) with relative humidity < 50%. If not properly handle and stored, the surface finish will be adversely affected by moisture and contaminates in the air.