How to control and protect the MSD component effectively!
The component with high humidity sensitivity
According to the standard, the MSD is mainly annoyed the non- hermetic SMD component. It includes the plastic sealing and packing material and other polymer such as wreath oxygen, the organic resin and so on. The IC, the chip, the electrolysis and electric capacity, the LED all belongs to the non-hermetic SMD.
The grade of the humidity sensitivity of the MSD is divided into 6 major types according to the J-STD-020 standard. The main difference among them is the floor life, the volume and the refluxing temperature of the welding surface. The main factors affecting the MSL are the Die attach material/process, Number of pins, Encapsulation (the mold compound or glob top) material/ process, Die pad area and shape, Body size, Passivation/die coating, Leadframe/substrate/and/or heat spreader design/ material/finish, Die size/thickness, Wafer fabrication technology/process, Interconnect, the Lead lock taping size/location as well as material.
The engineering research shows that the temperature of the smaller SMD component is higher than that of the big ones when they pass by the welding cooker with the same pre-set temperature curve.
The "volume" here means that the length multiply the breadth multiply the height and these sizes don't include the exterior pin, the "temperature" is pointed the surface temperature of the component.
The product whose grade of humidity sensitivity is grade 1 does not belong to the SMD component.
The damage principle to the credibility of the product leaded by the humidity sensitivity.
The water in the air will spread and permeate into the packing material of the MSD in the process of its exposition in the atmosphere. The component will reflux into the welding stove for welding after it is stick on the PCB and it should stop in the stove where the temperature is higher than 183 degrees, even the highest to 210 degrees to 235 degrees for 30 to 90 seconds. Its electronics function will be affected or damaged because of its layering or bursting leaded by that the water in the component inflates quickly and the conjunction between various materials loses regulation under the high temperature in the refluxing area. Like the breakage of the ESD, this damage can't be seen by naked eye under most circumstances and the MSD doesn't be expired completely in the test process.
Added: Tuesday, November 28, 2006
Submitter: meilysha | meilysha@126.com
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