Surface Mount Enclosures (SMD)

In order to properly perceive and use the material presented on SMD, you need to read the following information:

• The dimensions of the enclosures are very important, since apparently many enclosures are similar to each other, and to identify the device it is necessary to know not only the marking, but also the type of enclosure. But it can not save. Thus, the SOD80 case from PHILIPS has a diameter of 1.6 mm (nom.), While a number of other companies with the same name has a diameter of 1.4 mm, which is even smaller than the diameter of another, more compact PHILIPS SOD80C case. The SGS-Thomson type SOD15 enclosure is very similar to the 7043 and SMC enclosures, but does not match with them in the installation dimensions (see Table 2 in the chapter "Surface Mounting Enclosures (SMD)".
  
  
  
• There may be situations where manufacturers in the same building under the same marking put different devices. For example, the PHILIPS company places an NPN transistor type BC818W in a SOT323 type case and marks it with a 6H code, and MOTOROLA places a PNP transistor type MUN5131T1 in the same case with the 6H label. The same situation occurs within the same company. For example, the company SIEMENS in the case of SOT23 under the marking 1A produced transistors BC846A and SMBT3904, with different parameters. Such devices installed on the board can be distinguished only by the components surrounding them and, accordingly, by the switching circuit.
  
  
  
• Confusion exists not only with the marking, but also with the base of the enclosures. For example, a SOT-89 type case from ROHM, SIEMENS, TOSHIBA has a 1-2-3 pin-out (top view), while in PHILIPS, the same case has a 2-3-1 or 3-2-1 pin-out. In this book, the numbers of conclusions and their functional significance for different companies are given to a single denominator.
• The situation with passive components for surface mounting is no better. If the case is marked 103 (see the chapter "Surface Mount Enclosures (SMD)"), then this could be a 10 kΩ resistor, a 10 nF capacitor, or an inductance of 10 mH. If the case is marked 2R2, then it can be a resistor with a nominal value of 2.2 Ohm, and a capacitor with a capacity of 2.2 pF. Code 107 can mean 0.1 Ohm (Philips) or 100µF (Panasonic).
• In cases of type 0603, 0805, etc. unmarked can be located capacitor, inductance or resistor-jumper (Zero-Ohm, jumper).
• A colored bar or keyhole on SOD 123, D0215 type housings can indicate the cathode of a diode or the plus terminal of an electrolytic capacitor.
  
  
  
• In appearance, it is very difficult to distinguish R, C, and L from each other if they are located in cylindrical cases with leads and are marked with colored rings. But even after identification, it may be difficult to determine its parameters. For example, in practice, several techniques are used to color-code permanent capacitors (see the chapter "Capacitors. Color-marking").
  
  
  
• In absolutely identical cases with the same color code, a whole series of devices with different parameters can be produced. For example, the company MOTOROLA produces in the case of the SOD80 type, marked with one color ring, a whole series of zener diodes (51 devices) with stabilization voltage from 1.8 to 100 V and current from 0.1 to 1.7 A. In the same case PHILIPS manufactures a series of diodes.
• It is necessary to correctly determine the color of the marking itself. In practice, there may be difficulties with the difference of the following shades:
  Gray - St. blue - silver;
  blue - turquoise - electric;
  yellow - golden;
  Orange - St. brown - tobacco - beige.
• The black ring in the middle of the case can have not only resistors-jumpers (Zero-Ohm, jumper), but also other devices, especially taking into account the technological variation when marking.
• Many firms, in addition to the labeling principles specified in the International Electrotechnical Commission (IEC) Publications, use their in-house color and code markings. For example, there is a marking of SMD resistors when a colon is put instead of the number 8. In such cases, the marking 1:23 means 182 kΩ, and : 0R6 - 80.6 Ohms.
• SOT (SOD) - Small Outline Transistor (Diode) enclosures - literally means "transistor (diode) with small leads". At the present stage not only transistors and diodes, but also transistors with resistors, zener diodes, voltage stabilizers on the basis of an operational amplifier, and much more, are placed in SOT packages, and the number of outputs can be more than three. Standardization bodies do not keep pace with new developments of firms, and they are forced to introduce their new designations. For more information, see the "Enclosures" chapter.