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Marking method on SMT chip resistor
As an important component of SMT chip processing, chip resistors are generally small in size, so generally no words are printed on chip resistors, but numbers and letters are printed to indicate their resistance. What do these characters mean? Next, let me show you how to quickly identify these resistors.
1. Nominal method of digital cable position
J- means the accuracy is 5%, F- means the accuracy is 1%.
(1) 5% precision resistance value representation: the first two digits indicate effective real numbers, the third digit indicates how many zeros there are, the basic unit is Ω, for example: 302=3000=3KΩ, the third digit "2" means There are two zeros. Mostly used in E24 series.
(2) 1% precision resistance value representation: the first three digits are valid real numbers, the fourth digit indicates how many zeros there are, the basic unit is Ω, for example: 3002=30000Ω, the fourth digit "2" means there are two zero. Mostly used in E24 and E29 series.
(3) If it is a decimal, use R to represent the decimal point, such as: 3R5 represents 3.5Ω, R35 represents 0.35Ω
2. Nominal method of color circle
SMD resistors are the same as general resistors. Most of them use four rings (sometimes three rings) to indicate their resistance. The first ring and the second ring are significant numbers, and the third ring is the magnification. For example: "brown green black" means 15Ω; "blue gray orange silver" means "68kΩ" error ±10%.
3. E96 number code and letter mixed nominal method
The code tables of the E96 series need to be looked up. There is a special table, such as 39X, 39 represents 249, and X represents 10 to the -1 power, which is 24.9Ω.
Different SMT manufacturers have different printing rules for chip resistors, but in general, most of the rules follow the sub-rules.
The functional role of patch glue
SMT adhesive, or SMT patch adhesive, has a special role in SMT patch processing. The thermal hardening process of SMT patch adhesive is irreversible. Glue has this characteristic, so it is often produced together with the plug-in to complete the processing of the circuit board.
The functional role of patch glue
1. When performing SMT wave soldering, the components can be fixed on the circuit board to prevent the components from falling when the circuit board passes through the solder tank.
2. In the double-sided reflow soldering process, the application of patch glue can prevent the large components on the side that have been soldered from falling due to the heating and melting of the solder.
3. In the reflow soldering process and the pre-coating process, it can prevent displacement and stand-up during mounting.
4. SMT glue can be used for marking when the circuit board and components are changed in batches.
5. Facilitate the replacement of component varieties
6. Stable dispensing volume
7. Fast curing epoxy adhesive, thixotropic properties and air-free state. It is very suitable for high-speed placement machine dispensing, with good glue point shape control.
SMT patch glue is widely used in patch processing. For double-sided mounted circuit boards, SMT patch red glue is often used to prevent some components from falling. Since the use effect of the patch adhesive will be affected by the thermal curing conditions, the connected object, the equipment used and the operating environment, the selection of the patch adhesive should be determined according to the production process.
