The surface resistors have two main types, thick and thin film. Please check their details in the following:
SMD Resistor
- Thick film resistor:
The main material of the surface mount resistors thick film is the screening resistive film on the substrate surface with a flat shape and high purity alumina, which is opposed to the depositing resistive film that is on the round core as same as the axial resistors.
Varying the resistive paste before screening combined with laser trimming the film after screening decides the resistance value.
- Thin–film resistors:
Their resistive element is on a ceramic substrate with the protective coating on the component top and the positions of soldering on the sides.
Furthermore, there is an adhesion layer on the ceramic substrate of the positions of soldering, also there is dipped or plated solder coating after the nickel barrier underplating.
During the SMD soldering process, the nickel barrier is very critical to prevent the solderability of terminations for the reason that it can avoid the dissolution of the silver or gold electrode.
Generally speaking, resistors have various sizes and tolerance in 1/16, 1/10, 1/8, and ¼ watt ratings in 1 ohm to 100 megaohm resistance. Usually, the common sizes of resistors are including 0402, 0603, 0805, 1206, and 1210.
Commonly, there are colored resistive layers with protective coating on one side and generally a white base material on the other side for a surface mount resistor.
Hence, we can differentiate between the resistors and capacitors simply by their outer appearances.
- Tubular Passive SMD Components for SMT:
We can also call the cylindrical devices MELFs (metal electrode leadless faces), which is applicable for diodes, capacitors, ceramic and tantalum as well as resistors and jumpers.
They are cylindrical and the metal ends caps for soldering. Cylindrical metal electrode leadless faces are different from the rectangular resistors, which is not necessary to be mounted with resistive elements away from the board surface.
As similar to the traditional axial devices, for values, MELFs are color-coded. There are MLL 41 and MLL 34 for MELF diodes. Besides, for MELF resistors, there are four types: 0805, 1206, 1406, and 2309.
Tubular Passive SMD Components
- The Active SMDComponents
Ceramic packages always are expensive, so that’s the reason why the military applications industry commonly uses them to make high-end production.
On the contrary, nonmilitary applications assembly always use plastic SMD packages, because the nonmilitary sector does not need the hermiticity.
Because of CTE mismatch between the package and the substrate, there have to solder joint cracking for ceramic packages,
however, there are also concerns about plastic packages. The following is all the active SMD components for your reference:
Active SMD Components
- Small Outline Transistors (SOT):
In the surface mounting process, the small outline transistor is one of the forerunners of active devices.
Usually, they have three- and four-lead. SOT 23 (EIA TO 236) and SOT 89 (EIA TO 243) are the three-lead SOTs.
The four-lead device is including SOT 143 (EIA TO 253). Diodes and transistors generally use these packages.
When surface mounting small transistors, the SOT 23 and SOT 89 packages have become universal.
Besides, with the wide use of high pin count complex integrated circuits, the requirement of various types of SOTs and SODs are increasing.
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