What is smt:

SMT is the abbreviation of Surface Mounted Technology (SMT), which is the most popular technology and process in the electronic assembly industry.

What are the characteristics of SMT:

1. High assembly density, small size and light weight of electronic products. The volume and weight of patch components are only about 1/10 of traditional plug-in components. Generally, after SMT is used, the volume of electronic products is reduced by 40%~60%, and the weight

Reduced by 60%~80%.

2. High reliability and strong anti-vibration ability. Solder joint defect rate is low.

3. Good high-frequency characteristics. Reduced electromagnetic and radio frequency interference.

4. It is easy to realize automation and improve production efficiency. Reduce costs by 30% to 50%. Save material, energy, equipment, manpower, time, etc.

Why use SMT:

1. The pursuit of miniaturization of electronic products, the perforated plug-in components used in the past can no longer be reduced

2. The functions of electronic products are more complete, and the integrated circuits (ICs) used no longer have perforated components, especially large-scale and highly integrated ICs, and surface mount components have to be used.

3. For mass production and automatic production, the factory must produce high-quality products at low cost and high output to meet customer needs and strengthen market competitiveness

4. The development of electronic components, the development of integrated circuits (IC), and the multiple applications of semiconductor materials

5. The electronic technology revolution is imperative, and the pursuit of international trends

1. SMT process flow — single-sided assembly process

Incoming Material Inspection –> Silkscreen Solder Paste (Spot Adhesive) –> SMT –> Drying (Curing) –> Reflow Soldering –> Cleaning –> Inspection –> Repair

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2. SMT process flow — single-sided mixed assembly process

Incoming material inspection –> PCB A-side silk screen solder paste (point patch adhesive) –> SMD –> Drying (curing) –> Reflow soldering –> Cleaning –> Plug-in –> Wave soldering –> cleaning –>

Inspection –> Repair

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3. SMT process flow — double-sided assembly process

A: Incoming material inspection –> PCB A-side silk screen solder paste (dot patch adhesive) –> SMD –> Drying (curing) –> A-side reflow soldering –> Cleaning –> Flip board –> PCB B side screen printing

Solder paste (dot SMT adhesive) –> SMD –> Drying –> Reflow soldering (preferably only for B side –> Cleaning –> Inspection –>Rework)

This process is suitable for use when larger SMDs such as PLCC are mounted on both sides of the PCB.

B: Incoming material inspection –> PCB A-side silk screen solder paste (dot patch glue) –> SMD –> Drying (curing) –> A-side reflow soldering –> Cleaning –> Flip board –> B-side patch of PCB

Adhesive –> SMD –> Curing –> B-side wave soldering –> Cleaning –> Inspection –> Repair)

This process is suitable for reflow soldering on side A of PCB and wave soldering on side B. In the SMD assembled on the B side of the PCB, this process should be used when only SOT or SOIC (28) pins are below.

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4. SMT process flow — double-sided mixed assembly process

A: Incoming material inspection –> SMD glue on the B side of the PCB –> SMT –> Curing –> Flip board –> Plug-in on the A side of the PCB –> Wave soldering –> Cleaning –> Inspection –> Repair

Paste first and then insert, suitable for the situation where there are more SMD components than discrete components

B: Incoming material detection –> Plug-in on side A of PCB (pins are bent) –> Flip board –> SMT glue on B side of PCB –> Patch –> Curing –> Flip board- -> Wave Soldering–> Cleaning

–> Inspection –> Repair

Insert first and stick later, suitable for the situation where there are more discrete components than SMD components

C: Incoming material inspection –> PCB A side screen printing solder paste –> patch –> drying –> reflow soldering –> plug-in, pin bending –> flip board –> PCB B Paste patch glue –> patch

–> Curing –> Flip board –> Wave soldering –> Cleaning –> Inspection –> Repair

The A side is mixed, and the B side is mounted.

D: Incoming material inspection –> SMT glue on the B side of the PCB –> SMD –> Curing –> Flip board –> Screen printing solder paste on the A side of the PCB –> SMD –> A side Reflow soldering –> Plug-in –>

B side wave soldering –> Cleaning –> Inspection –> Repair

The A side is mixed, and the B side is mounted. Paste double-sided SMD first, reflow soldering, then insert, wave soldering

E: Incoming material inspection –> PCB B-side silk screen solder paste (dot patch adhesive) –> SMD –> Drying (curing) –> Reflow soldering –> Flip board –> PCB A Surface screen printing solder paste –> patch

–> Drying –> Reflow soldering 1 (partial soldering can be used) –> Plug-in –> Wave soldering 2 (If there are few inserted components, manual soldering can be used) –> Cleaning –> Inspection –> rework

SMT basic process composition:

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Elements of the basic process:

Silk screen printing (or dispensing) –> Mounting –> (curing) –> Reflow soldering –> Cleaning –> Inspection –> Repair

Silk screen printing: Its function is to print solder paste or patch glue onto the pads of PCB to prepare for the soldering of components. The equipment used is a screen printing machine (screen printing machine), which is located at the forefront of the SMT production line.

Glue dispensing: It is to drop glue onto the fixed position of the PCB, and its main function is to fix the components to the PCB. The equipment used is a glue dispenser, which is located at the front end of the SMT production line or after the testing equipment

noodle.

Mounting: Its function is to accurately install the surface mount components to the fixed position of the PCB. The equipment used is a placement machine, which is located behind the screen printing machine in the SMT production line.

Curing: Its function is to melt the patch adhesive, so that the surface mount components and the PCB board are firmly bonded together. The equipment used is a curing oven, which is located behind the placement machine in the SMT production line.

Reflow soldering: Its function is to melt the solder paste, so that the surface mount components and the PCB board are firmly bonded together. The equipment used is a reflow oven, which is located behind the placement machine in the SMT production line.

Cleaning: Its function is to remove the welding residues harmful to human body such as flux on the assembled PCB board. The equipment used is a washing machine, and the location may not be fixed, online or offline.

Inspection: Its function is to inspect the welding quality and assembly quality of the assembled PCB board. The equipment used is magnifying glass, microscope, online tester (ICT), flying probe tester, automatic optical inspection

(AOI), X-RAY inspection system, functional tester, etc. The location can be configured in a suitable place on the production line according to the needs of detection.

Rework: Its function is to rework the PCB boards that have detected failures. The tools used are soldering iron, rework station, etc. Configured anywhere in the production line.

Technical components related to SMT

1. Design and manufacturing technology of electronic components and integrated circuits

2. Circuit design technology of electronic products

3. Manufacturing technology of circuit board

4. Design and manufacturing technology of automatic placement equipment

5. Circuit assembly manufacturing technology

6. Development and production technology of auxiliary materials used in assembly manufacturing

Why use Surface Mount Technology (SMT)?

1. The pursuit of miniaturization of electronic products, the perforated plug-in components used in the past can no longer be reduced

2. The functions of electronic products are more complete, and the integrated circuits (IC) used no longer have perforated components, especially large-scale and highly integrated ICs, and surface mount components have to be used

3. For mass production and automatic production, the factory must produce high-quality products at low cost and high output to meet customer needs and strengthen market competitiveness

4. The development of electronic components, the development of integrated circuits (IC), and the multiple applications of semiconductor materials

5. The electronic technology revolution is imperative, and the pursuit of international trends

Features of SMT

1. High assembly density, small size and light weight of electronic products. The volume and weight of patch components are only about 1/10 of traditional plug-in components. Generally, after SMT is used, the volume of electronic products is reduced by 40%~60%, and the weight

Reduced by 60%~80%.

2. High reliability and strong anti-vibration ability. Solder joint defect rate is low.

3. Good high-frequency characteristics. Reduced electromagnetic and radio frequency interference.

4. It is easy to realize automation and improve production efficiency. Reduce costs by 30% to 50%. Save material, energy, equipment, manpower, time, etc.

Introduction of SMT components

SMC: Surface Mounted components (Surface Mounted commponents)

There are mainly rectangular chip components, cylindrical chip components, composite chip components, and special-shaped chip components.

SMD: Surface Mounted Devices

There are mainly chip transistors and integrated circuits, and integrated circuits include SOP, SOJ, PLCC, LCCC, QFP, BGA, CSP, FC, MCM, etc. Examples are as follows:

1. Connector (Interconnect): Provides mechanical and electrical connection/disconnection, consisting of connecting plugs and sockets, connecting cables, brackets, chassis or other PCBs to PCBs;

Connections must be via surface mount type contacts.

2. Active electronic components (Active): In analog or digital circuits, voltage and current can be controlled by themselves to generate gain or switching effects, that is, to respond to applied signals and change their basic

Features. Passive electronic components (Inactive): do not change their own characteristics when an electrical signal is applied, that is, provide a simple, repeatable response.

3. Odd-form electronic components (Odd-form): The geometry factor is peculiar, but not necessarily unique. Therefore, it must be mounted by hand, and the shape of its shell (compared to its basic function) is non-standard.

Examples: many transformers, hybrid circuit structures, fans, mechanical switch blocks, etc.

Chip resistors, capacitors, etc., size specifications: 0201, 0402, 0603, 0805, 1206, 1210, 2010, etc. Tantalum Capacitors, Dimensions:

TANA, TANB, TANC, TANDSOT

Transistor, SOT23, SOT143, SOT89, etc.

Melf cylindrical components, diodes, resistors, etc.

SOIC integrated circuit, size specification: SOIC08, 14, 16, 18, 20, 24, 28, 32

QFP Fine pitch integrated circuit PLCC integrated circuit, PLCC20, 28, 32, 44, 52, 68, 84

BGA ball grid array packaging integrated circuits, array spacing specifications: 1.27, 1.00, 0.80

CSP Integrated circuit, the side length of the component is not more than 1.2 times the side length of the inner chip, and the microBGA with the array pitch <0.50

Explanation of SMT terms

Bridge (Tin Bridge): Solder that connects two conductors that should be electrically connected, causing a short circuit.

Buried via: A conductive connection between two or more inner layers of a PCB (ie, invisible from the outer layers).

C.

CAD/CAM system (Computer-aided design and manufacturing system): Computer-aided design uses specialized software tools to design printed circuit structures; computer-aided manufacturing converts this design into actual products

Taste. These systems include large-scale memory for data processing and storage, input for design creation, and output devices for converting stored information into graphics and reports

Capillary action: A natural phenomenon in which molten solder flows against the force of gravity on solid surfaces that are very close together.

Chip on board (COB board chip): A hybrid technology that uses face-up glued chip components, traditionally connected exclusively to the substrate layer of the circuit board by flying leads.

Circuit tester (circuit tester): A method of testing PCBs during mass production. Includes: Bed of Needles, Component Pin Footprint, Guide Probes, Internal Traces, Loaded Board, Empty Board, and Component Test.

Cladding (covering layer): A thin layer of metal foil is bonded to the board layer to form PCB conductive wiring.

Coefficient of the thermal expansion (temperature expansion coefficient): when the surface temperature of the material increases, the measured material expansion per million parts per degree temperature (ppm)

Cold cleaning (cold cleaning): an organic dissolution process, liquid contact to complete the removal of residue after welding.

Cold solder joint (cold solder joint): A solder joint that reflects insufficient wetting, characterized by a gray, porous appearance due to insufficient heating or improper cleaning.

Component density (component density): the number of components on the PCB divided by the area of the board.

Conductive epoxy: a polymeric material, by adding metal particles, usually silver, to pass an electric current.

Conductive ink (conductive ink): glue used on thick film materials to form PCB conductive wiring diagrams.

Conformal coating: A thin protective coating applied to a PCB that conforms to the shape of the assembly.

Copper foil (copper foil): A negative electrolytic material, a thin, continuous layer of metal foil deposited on the base layer of the circuit board, which acts as a conductor for the PCB. It adheres easily to the insulating layer, accepts printing protection

The protective layer forms a circuit pattern after corrosion. Copper mirror test: A flux corrosion test using a vacuum deposited film on a glass plate.

Cure (baking curing): The change in the physical properties of the material, through chemical reaction, or pressure/non-pressure reaction to heat.

Cycle rate (cycle rate): a term for component placement, used to measure the machine speed from picking up, positioning on the board and returning, also called test speed.

D.

Data recorder: A device that measures and collects temperature from a thermocouple attached to a PCB at specific time intervals.

Defect: A component or circuit unit that deviates from normally accepted characteristics.

Delamination: Separation of the ply and separation between the ply and the conductive covering.

Desoldering (unsoldering): To disassemble the welding components for repair or replacement. The methods include: absorbing tin with a tin absorber, vacuum (solder straw) and hot drawing.

Dewetting (dewetting): The process in which the molten solder is first covered and then retracted, leaving irregular residues.

DFM (Design for Manufacturing): A method of producing a product in the most efficient manner, taking into account time, cost and available resources.

Dispersant: A chemical that is added to water to increase its ability to remove particles.

Documentation: Information about assembly, explaining basic design concepts, types and quantities of components and materials, special manufacturing instructions, and latest versions. Use three types: Prototype and Few

Volume runs, standard production lines and/or production quantities, and those government contracts specifying actual figures.

Downtime (Downtime): The time when equipment is not producing products due to maintenance or failure.

Durometer (hardness tester): Measure the rubber or plastic hardness of the scraper blade.

E.

Environmental test: A test or series of tests used to determine the total external influence on the structural, mechanical, and functional integrity of a given component package or assembly.

Eutectic solders: Alloys of two or more metals with the lowest melting point that, when heated, change directly from solid to liquid without going through the plastic phase.

F

Fabrication(): The empty board manufacturing process after design and before assembly. The individual processes include stacking, metal addition/subtraction, drilling, plating, wiring, and cleaning.

Fiducial (fiducial point): a special mark integrated with the circuit wiring diagram, used for machine vision to find out the direction and position of the wiring diagram.

Fillet: The connection formed by solder between the pad and the component pin. That is, solder joints.

Fine-pitch technology (FPT fine-pitch technology): The distance between the centers of the pins of the surface mount component package is 0.025″ (0.635mm) or less.

Fixture: A device that connects the PCB to the center of the processing machine.

Flip chip (flip chip): A leadless structure, generally containing circuit units. Designed to be electrically and mechanically connected by an appropriate number of solder balls (covered with conductive adhesive) on its face

connected to the circuit.

Full liquidus temperature: The temperature level at which the solder reaches its maximum liquid state, most suitable for good wetting.

Functional test (functional test): Simulate its expected operating environment, and test the electrical appliances of the entire assembly.

G

Golden boy: A component or circuit assembly that has been tested and known to function to specification and is used to test other units by comparison.

h

Halides: Compounds containing fluorine, chlorine, bromine, iodine, or astatine. Is the catalyst part of the flux and must be removed due to its corrosiveness.

Hard water: Water containing calcium carbonate and other ions that may collect on the interior surfaces of clean equipment and cause clogging.

Hardener: A chemical added to the resin to make it harden in advance, that is, a curing agent.

I

In-circuit test (online test): A component-by-component test to verify the placement and orientation of components.

J

Just-in-time (JIT just on time): Minimize inventory by supplying materials and components directly to the production line before going into production.

L.

Lead configuration (pin shape): The conductor extending from the component acts as a mechanical and electrical connection point.

Line certification (production line confirmation): confirm that the sequence of the production line is controlled, and reliable PCBs can be produced according to the requirements.

M

Machine vision (machine vision): One or more cameras are used to help find the component center or improve the component placement accuracy of the system.

Mean time between failure (MTBF average time between failures): the average statistical time interval between expected possible operating unit failures, usually calculated per hour, the results should indicate the actual, predicted

Calculated or calculated.

N

Nonwetting: A condition in which solder does not adhere to the metal surface. Non-wetting is characterized by visible bare base metal due to contamination of the surfaces to be welded.

o

Omegameter: An instrument used to measure the amount of residual ions on the surface of a PCB by immersing the assembly in a mixture of alcohol and water of known high resistivity, thereafter, measuring and recording

The resulting resistivity drops. Open (open circuit): The points of two electrical connections (pins and pads) become separated, either because of insufficient solder or poor coplanarity of the pins at the connection point.

Organic activated (OA organic activity): organic acid as a flux system active agent, water-soluble.

P

Packaging density (assembly density): the number of components (active/passive components, connectors, etc.) placed on the PCB; expressed as low, medium or high.

Photoploter (photo plotter): Basic wiring diagram processing equipment used to produce original PCB layout diagrams (usually actual size) on photographic negatives.

Pick-and-place (pick-and-place equipment): a programmable machine with a robotic arm that picks up components from an automatic feeder, moves them to a fixed point on the PCB, and places them in the correct position in the correct direction.

set.

Placement equipment (mounting equipment): a machine that places components on the PCB in combination with high speed and accurate positioning. It is divided into three types: SMD mass transfer, X/Y positioning and online transfer system, which can be combined with

Adapt the components to the board design.

R

Reflow soldering (reflow soldering): Through various stages, including: preheating, stabilization/drying, reflow peak and cooling, the process of placing surface mount components into solder paste to achieve permanent connection.

Repair: The action of restoring the function of a defective assembly.

Repeatability (repeatability): the process ability to accurately return to the characteristic target. An indicator for evaluating processing equipment and its continuity.

Rework: A repetitive process of bringing an incorrect assembly back to specification or contract.

Rheology (Rheology): Describes the flow of liquids, or their viscosity and surface tension properties, such as solder paste.

S

Saponifier: An aqueous solution of organic or inorganic ingredients and additives used to facilitate removal of rosin and water-soluble fluxes by, for example, dispersible cleaners.

Schematic: A diagram that uses symbols to represent a circuit arrangement, including electrical connections, components, and functions.

Semi-aqueous cleaning: A technique involving solvent cleaning, hot water rinsing, and drying cycles.

Shadowing (shadow): In infrared reflow soldering, the component body blocks energy from certain areas, resulting in insufficient temperature to completely melt the solder paste.

Silver chromate test: A qualitative check for the presence of halide ions in RMA flux. (RMA Reliability, Maintainability and Availability)

Slump: Diffusion of materials such as solder paste and glue before curing after stencil printing.

Solder bump (solder ball): The spherical solder material is bonded to the contact area of passive or active components, and plays the role of connecting with the circuit pad.

Solderability: The ability of a conductor (pin, pad, or trace) to wet (become solderable) in order to form a strong connection.

Soldermask (solder mask): The processing technology of printed circuit boards, except for the connection points to be soldered, all surfaces are covered with plastic coating.

Solids (solid): in the flux formula, the weight percentage of rosin, (solid content)

Solidus: The temperature at which the solder alloy of some components begins to melt (liquefy).

Statistical process control (SPC Statistical Process Control): The use of statistical techniques to analyze process output, use the results to guide actions, adjust and/or maintain quality control status.

Storage life (storage life): The storage and usefulness of the glue.

Subtractive process: A circuit layout obtained by removing selected portions of a conductive metal foil or overlay.

Surfactant: A chemical added to water to lower surface tension and improve wetting.

Syringe: A container of glue that drips through its narrow opening.

T.

Tape-and-reel (tape and reel): component packaging for patch, on a continuous strip, the component is loaded into the pit, the pit is covered by a plastic tape, so that it can be rolled onto the reel for component patching Machine use.

Thermocouple: A sensor made of two dissimilar metals that, when heated, produces a small DC voltage in temperature measurement.

Type I, II, III assembly (first, second, and third types of assembly): PCB (I) with surface mount components on one or both sides of the board; pin components are mounted on the main surface, and SMD components are mounted on one side or two-sided

Hybrid technology (II); Hybrid technology (III) characterized by passive SMD components mounted on the second side and pin (through-hole) components mounted on the main side.

Tombstoning (component standing): A welding defect in which a chip component is pulled into a vertical position so that the other end is not welded.

U

Ultra-fine-pitch (ultra-fine-pitch): The center-to-center distance of the pin and the conductor spacing are 0.010” (0.25mm) or less.

V

Vapor degreaser (vapor degreaser): A cleaning system that suspends the object in the box and the heated solvent vapor condenses on the surface of the object.

Void (void): The cavity inside the tin point, formed by the release of gas during reflow or the residue of flux trapped before solidification.

Y

Yield (yield rate): The ratio of the number of components used at the end of the manufacturing process to the number of components submitted for production.

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