Description
Moisture Barrier Bag (MBB)
It is essential to keep Surface-Mount Devices (SMDs) dry from manufacturing point to the time of reflow soldering. Moisture Barrier Bag, also known as Vapor Barrier Bag, is made by multiple layers of plastic and a thin aluminum layer or aluminized layer that controls moisture vapor leakage. Basically, there are 3 kinds of Moisture Barrier Bags (MBBs), Tyvek MBB, AMBB and ANMBB, in the market. The key factor of moisture barrier function of the bag is a metal layer or a metalized layer, like thickness of the foil layer, metalized layer, etc., but the thickness or the material of other layers also affects the quality of MBB as well.
Thickness units
Mil – 0.001 inch, ex) 3 mils = 0.003 x 25.4 mm = 0.0762 mm = 76.2 microns
Micron – 1/1,000,000 m (1/1,000 mm = 0.001 mm), ex.) 100 microns = 100/25.4 = 3.93 mils
MM – 0.15 mm = 150 microns
MVTR
The Moisture Vapor Transmission Rate (MVTR) is the rate that water vapor passes through a specific area of barrier material. MVTR is measured in grams of water vapor per 100 square inches of barrier per 24 hours (g/100 in.2/24 h). EIA 583 Packaging Material Standards for Moisture-Sensitive Items defindes a Class 1 barrier as having an MVTR of <0.02 g/100 in.2/24 h. A Class 2 barrier is set at <0.08 g/100 in.2/24 h. |