Various types of SMD | SMD resistors | SMD capacitor | SMD IC | Some numerical |
Various types of SMD:
1. SMD Resistors:
There are two types of Surface mount resistors like;
i. Thick film ii. Thin film
The difference between the thin film and thick film resistors is not the actual thickness of the film, but how the film applied to the surface.
Thick film surface mount resistors are constructed by screening resistive film on a flat, high purity alumina substrate surface. The resistance value is obtained by varying the composition of resistive paste before screening and laser trimming the film after screening.
For thin-film resistors, the resistive element on the ceramic substrate with a protective coating like glass on top and solderable terminations made of tin-lead on the sides. Silver and nickel will provide preservation for the solderability of termination.
SMD resistors are available in 1/16, 1/10, 1/8, ¼ watt rating in 1 Ω to 100 MΩ resistance in various sizes and various tolerance. Thin-film resistors are generally specified with 0.1, 0.2, 0.5, or 1% tolerances with a temperature coefficient of 5 to 25 ppm/k.
Thick film resistors are generally specified with 2 % or 1 % tolerance with higher temperature coefficients typically ±200 or ±250 ppm/k. Thin-film resistors are expensive than thick film resistors. Surface-mount resistors are as shown in the figure.
All SMD resistors are also available as ‘Zero-ohm resistors’ which will use in place of wire links. SMD resistors print with numerical values in code with standard tolerances.
All SMD resistors marked with a three-digit code, in which the first two digits are the first two significant digits of the value and the third digit is the power of ten.
- 334= 33 x 104= 330kΩ
- 473=47 x 103= 47kΩ
- 105= 10 x 105= 1MΩ
Resistance less than 10 Ω have R to indicate the position of the decimal point.
- 0R22= 0.22 Ω
- 4R7 = 4.7 Ω
Precision resistors are marked with four-digit code in which the first three digits are three significant digits of the value and 4th digit is the power of ten.
- 1001= 100 x 103 = 1kΩ.
- 4992= 499 x 102 = 49.9 kΩ.
000 and 0000 marked SMD resistors are zero-ohm links with approximately zero resistance. Surface mount resistor networks or R-packs used as a replacement for a series of resistors.
2. Various types of SMD (Surface mount ceramic) capacitor:
SMD means Surface mount capacitors are ideal for high-frequency circuit applications because it does not have any leads and can place underneath the package on the opposite side of the PCB.
Surface mount capacitors used for both decoupling applications and for frequency control. Multilayer monolithic capacitors have improved volumetric efficiency. Surface mount capacitors are highly reliable.
SMD capacitors used in automotive applications, military equipment, and aerospace applications. SMD ceramic capacitor is as shown in the figure.
3. Surface mount tantalum capacitors:
For surface mount capacitors, the dielectric can either be ceramic or tantalum. Surface mount tantalum capacitors offer very high volumetric efficiency or high capacitance voltage product per unit volume and high reliability.
Plastic molded tantalum capacitors have leads instead of terminations and are available in two case sizes standard and extended range. The capacitance value for tantalum capacitors varies from 0.1 to 100 µF from 4 to 5 V dc in different case sizes.
Tantalum capacitors are available with or without marked capacitance value. The surface-mount tantalum capacitor is as shown in the figure.
4. Various types of SMD Active components for SMT (Plastic Packages):
Ceramic packages are expensive and mainly used for military applications. Plastic SMD packages are most widely used for non-military applications.
SMD active component plastic packages are as follows:
1. Small outline transistors (SOT)
2. Small outline integrated circuit (SOIC and SOP)
i. Small outline transistors (SOT):
Small outline transistors are active devices in surface mounting.
They are three and four lead device. Three-leads SOTs are identified as SOT-23 and SOT-89.
Four-lead SOTs are SOT 143 packages. SOT-23 and SOT 143 packages.
SOT-23 and SOT-89 these packages are used for surface mounting small transistors.
Small outline transistors (SOTs) are as shown in the figure.
SOT- 23 and SOT-143 packages are used for power dissipation 200mW to 400mW.
SOT-89 are used for power dissipate 500mW to 1W.
ii. Small outline Integrated Circuits:
The small outline integrated circuit is basically a shrink package with leads on 0.050 inch centers.
SOICs are used to assemble multiple SOTs. Thus numbers of SOTs are combined in single SOIC.
SOIC contains leads on two sides that are formed outward.
SOICs need to be handled carefully to prevent lead damage. SOICs are available in two different body widths 150 mils and 300 mils.
The body width of packages having fewer than 16 leads is 150mil and for more than 16 leads, 300 mil width is used.
16 leads package is available in both body widths.
SOICs are as shown in the figure. SMD ICs are electrically compatible with DIL that is dual inline cases. Small outline packages produced with two different pin forms.
i. Pins bent outside of the case.
ii. Pins bent under the case.
Following figure shows different so case forms.
Different case types have different pin forms and pinouts. Small outline (SO) used for ICs with 8 to 28 pins. VSO (Very small outline) use for ICs with more than 28 pins.
5. Plastic leaded chip carriers (PLCC):
The plastic leaded chip carrier (PLCC) is a cheaper version of the ceramic chip carrier. PLCC cases will use for ICs with more than 28 pins.
For the PLCC case pins will place on all four sides of the case and bent under it. The leads in PLCC takes solder joint stress and prevent solder joint cracking.
Some PLCC need proper handling to avoid package cracking due to moisture absorption. The figure shows a plastic leaded chip carrier.
6. Small outline J packages (SOJ):
The SOJ packages have J-bend leads like PLCC, but they have pins only on the two sides. This package is a hybrid of SOIC and PLCC.
Thus SOJ package provides handling benefits of PLCC and space efficiency of SOIC.
The SOJs mainly use for high density (1 MB, 4 MB, and 16 MB) DRAMs. The figure shows a small outline J package.
7. Fine pitch SMD packages (QFP, SQFP):
SMD packages with very fine pitch and a large number of leads that called a fine pitch package. Quad flat pack (QFP) and shrink quad flat pack (SQFP) are fine pitch packages.
QFP (Quad flat pack case) will use for ICs with very high count of pins (over 100). These pins will bent outside of the case.
Fine pitch packages have thinner leads and require thinner land pattern design. Figure shows fine pitch packages.
8. Ball Grid Array (BGA):
BGA or Ball Grid Array packages are like PGA that is pin grid array but without the leads.
BGAs are available in ceramic or plastic forms. The body Size of BGAs vary from 7 to 50mm and their pins counts vary from 16 to 2400.
Mostly BGAs pin counts range between 200 and 500 pins. BGAs are very good for self-alignment, even if they will misplace by 50%. The figure shows the BGA package.
9. Various types of Land patter of SMD:
The SMT process requires the SMDs footprints that will the hard copper pattern called land, on the circuit board upon which the SMD will place.
The footprint that is land pattern also includes the position of solder resist pattern surrounding the copper pattern.
In SMDs land design very important for the placement of components. Same as PCB component layout.
The design of the land pattern of the SMD requires thermal consideration also. A small SMD package has less heat carrying capacity.
The figure shows the land pattern of the IC in a typical quad flat package. The figure shows two terminal packages used as resistors or capacitors.
The number provided with the package gives length and width dimensions. These packages have end terminations that design to rest on substrate lands.
- SMD will use in CTV tuners.
- It will used in the electronic telephone.
- Used in radio and disc drivers.
- Used in pocket calculators.
- SMD will use in an embedded systems.
- Used in VLSI design.