Humidity Control Storage Cabinet in Printed Circuit Board Manufacturing
Printed Circuit Boards are hygroscopic and will absorb moisture from the ambient environment.
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.
Image sourced from : Bob Willis [email protected] www.Bobwillis.co.uk /
PCB Delamination with Bob Willis https://www.youtube.com/watch?v=pn7P-knw_lg&feature=youtu.be
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 degradesolderability 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 solderabilityissues if the intermetallic layer reaches the surface and oxidizes.
Organic Solderability Preservative Coatings
Organic solderability preservative (OSP) coatings provides solderability, ease of processing and low cost. OSP coatings are among the leading surface finish options in lead free soldering. However, compared to alternatives, OSP are most prone to oxidation due to the pure copper surface protected only by the OSP coating layer.
IPC-1601 states “Baking is NOT recommended for OSP coatings, as it deteriorates the OSP finish. If baking is deemed necessary, the use of the lowest possible temperature and dwell time is suggested as a starting point.”
Moisture can be removed from PCBs with Eureka’s ultra low humidity Fast Super Dryers without high temperatures causing damages. The powerful multi-porous molecular sieve desiccants utilized by Eureka’s core units adsorb the moisture from the PCBs while protecting against oxidation and intermetallic growth. Eureka’s Fast Super Dryer are IPC/JEDEC compliant, suitable for safe storage of PCBs infinitely.
Electroless nickel immersion gold (ENIG)
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.
Epoxy glass prepreg contains moisture and requires specific storage environments. If prepreg absorbs excessive moisture, its bonding strength could be weakened. Long term storage of prepregs typically requires 5°C with relative humidity of 50%. Remaining unused prepregs should be stored stored flat (horizontally) in a in a cool, dry environment such as a dry cabinet—typically at 23°C or lower and 50%RH or lower, and sealed in a moisture barrier bag (MBB).
Clearly, various material in PCB manufacturing requires specific storage environments. Proper storage and handling of these materials will affect the overall quality of the final product. For alternative drying methods and protection of PCB manufacturing materials from moisture related harm, Eureka recommends our Series SMT dry cabinet for storage of manufacturing material to maximize shelf life and increase the reliability of your product. today for further information about our Fast Super Dryer or inquire about how to become an agent, distributor or dealer.