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The Ultimate Guide to SMT PCB Assembly: Surface Mount Technology(SMT)

What is Surface Mount Technology(SMT) PCB?

What is a Surface Mount?

SMT PCB assembly is a highly precise method of placing electronic components because it is automatic and is easy to carry out on properly equipped production lines. Machines designed for SMT assembly can quickly implement serial production, ensuring full repeatability of the created electronic components.

SMD Components

SMT PCB assembly of this type is easy to carry out with the use of many SMD elements, which are ultimate to place on the printed circuit board. These types of components include, among others integrated circuits, diodes, sensors, resistors, capacitors, fuses, resistors, and rectifiers.

Due to the small size of SMD components, they do not have value and color code markings. Similarly, these components are also very sensitive to the occurrence of overvoltage and electrostatic discharges. Therefore, assembly works with their use must take place in a properly protected environment.

Soldering of SMD Components in Surface Mounting

Surface mounting requires proper soldering of elements that place on printed circuit boards. Moreover, this technology allows them to come on both sides. Subsequently, SMD components mount on the laminate, with previously prepared places and connection paths. In the case of double-sided installation, fixing carries out with the use of a special glue.

Moreover, the solder pads cover with a paste containing flux and tin solder. The joining process carries out using regulated, hot air and blowing force. In this case, hand soldering irons are not good to use, due to the high risk of accidental damage to the laminate or the entire SMD component.

SMT pcb assembly carries out in an automated manner. Similarly, it allows for significant miniaturization of the created electronic devices and obtaining a high density of elements arrangement. Components are easy to mount on both sides of the board, achieving low connection impedance and better product properties at high frequencies.

This technology ensures very good mechanical strength of the products under vibration or shock conditions, due to the low weight of the elements. Furthermore, very high production speed with relatively low assembly costs is also important.

Features of SMT PCB Assembly

Basically, the most popular way to place SMD components on a PCB is surface mount. Electronic elements attach to the product using a special solder paste.

SMT Technology

The choice of surface placement technique depends on the set of elements, technology features, and design of nodes. The production of PP by this method has several differences:

The possibility of reducing the dimensions of the product, the area of ​​placement of components due to the minimum size of printed elements, the use of double-sided mounting, and the absence of additional microcircuit outputs;
Compact placement, dense layout, increased tracing density;
Similarly, reliability of the design, reducing the number of materials good to use;
Cost reduction due to the absence of the need for additional operations to prepare the outputs of elements, drilling mounting holes;
Furthermore, the possibility of automating the process, reducing the cost of serial products;
Improved signal transmission quality;
Subsequently, Increased maintainability due to easy dismantling, and installation of new elements without the risk of damage to adjacent blocks.
SMT technology allows you to speed up the process of mounting a printed circuit board.

SMT PCB Assembly Steps

For systems with various electronic components, surface fixation can be good to use with simultaneous soldering of the element base into the holes. For the manufacture of complex structural units, special, increased requirements impose on the technological process in terms of reliability and functionality. Subsequently, the main stages of smt pcb assembly installation:
Applying the required dose of solder paste to the contact pads (it is possible to use screen printing to obtain a pattern);
Installation of electronic components, and elements on a printed circuit board;
Moreover, solder reflow using infrared, temperature heating, convection, laser, or wave;
Cleaning the product, and applying a protective layer.

Surface mounting of printed circuit boards has become widespread due to many features. The technology allows you to place a large number of SMD components on a board with a small area.

SMD Mounting Process

SMD components are parts with contacts in the form of small legs or pads. Their small size allows them to come at a high density. In addition, SMD mounting during smt pcb assembly allows you to fix components on both sides of the board.

The elements solder to pre-prepared pads. The technological process of surface mounting involves several stages. Similarly, strict adherence to technology at every step allows you to get a quality product.

Marking

The technology involves applying appropriate markings to the surface of the board. It is necessary to control the production process. Drawing a pattern on the surface of a textolite element is easy to carry out in several ways:
Using a stencil. White, black, or yellow paint is good to use. The stencil allows you to correctly place the pattern and avoid getting paint on adjacent surfaces.
Using an inkjet printer. This is specialized labeling equipment. This method is widely good to use in serial production. Inkjet printers are easy to integrate into production lines. This allows you to optimize your workflow.
Using laser technology. Equipment is easy to integrate into production lines. Moreover, laser technology allows drawing with high precision. At the same time, the devices distinguish by a high degree of automation.

The use of equipment with conveyor lines can significantly increase its productivity.

Applying Solder and Solder Paste during SMT PCB Assembly

Surface mount technology involves the use of solder paste. It is good to use to set items. Solder paste is a mixture containing fine solder particles, flux, binders, and additional additives.

Basically, mounting SMD components requires precise dosing of solder paste. Correct placement of the composition and strict observance of the layer thickness is necessary. The paste is applied to the printed circuit board using a specialized printer. It comes with stencils for the correct placement of the composition on the surface.

Installing SMD Components on a Printed Circuit Board

Elements can come on one or both sides of the PCB. To increase the speed of installation of parts, automatic machines are good to use. Subsequently, the use of such equipment allows you to place components with high accuracy and density.

Machines for installing SMD components on a printed circuit board are characterized by a high degree of automation. Participation in the process of the operator is not achievable. In addition, this increases productivity and reduces the risk of scrap.

Soldering SMD Components

Given the features of surface mounting, it is possible to solder components in several ways:
In a convection oven. Parts get heat by supplying a jet of hot air to them. Such ovens come with conveyor belts to gradually move the product between zones with different temperatures. Similarly, this ensures uniform heating. When hot air is supplied, the contact pads are soldered together.
in the vapor phase. The method involves heating the elements due to the high temperature of the steam. Furthermore, it occurs when inert liquids boil. Soldering carries out in special chambers that prevent air from entering. This eliminates the formation of an oxide film upon interaction with oxygen.
With the help of infrared radiation. This method involves heating due to IR rays directed at the part. Semi-automatic and automatic soldering machines are good to use in production. Subsequently, they provide a uniform increase in temperature and exclude overheating of parts.

These soldering methods make it possible to mount SMD elements with high quality.

How Does SMT Work?

SMD fixation of electronic components carries out in several successive stages:
study of technical documentation for the manufacture of microcircuits;
Similarly, creating stencils;
Preparation of the production process;
Furthermore, application and distribution of solder paste;
Installation of SMD elements;
In addition, group soldering of boards in an oven;
Washing and drying finished microcircuits;
OTC check.

Generally, Stencils come mainly from hard grades of stainless steel sheets. Holes come in the plates, coinciding with the soldering points of the leads to the contact pads. Similarly, powdered solder paste distributes through apertures on the board.

After that, chips come on it and then the plate is heat-treated in an oven. When heated, the paste spreads. Moreover, the flux included in it cleans the working surface, and the solder provides a molecular connection of contacts with metalized tracks.

After that, the finished board is washed and dried, if necessary, flux residues remove. The next step (if required) is to install the output components. Moreover, the production process ends with a quality control check.

With the help of testers, the parameters of the operation of individual elements and the microcircuit as a whole are measured. The obtained values ​​compare with those declared in the technical documentation.

The Advantages and Disadvantages of SMT PCB Assembly

Benefits of Surface Mount Technology

SMD components are in demand due to their size. With their help, one-sided and double-sided boards of high quality are easy to produce. The technology is in demand in production due to some advantages:

1. Reducing the weight and overall parameters of the finished product. The installation method allows you to place high-density parts on both sides of the plate.
2. Possibility of repair. In case of failure, the element is easy to replace with a new one.
3. Moreover, possibility of automatic installation. Reduces the risk of marriage. There is no need to attract a large number of operators.
4. High performance. There is no need to make holes in the plate. Components are installed directly on the pads.

Thanks to the use of automatic machines insmt pcb assembly, high-quality boards is easy to obtain. At the same time, the small dimensions of the parts reduce the cost of materials.

Disadvantages of Surface Pasting Technology

SMT is made with small size, and narrow distance, so it is more difficult to repair.

Similarly, the solder that can be good to use in PCB production by automation technology is less and less. SMT can only be done by automation devices. This requires manufacturing enterprises to invest in machinery and equipment. This is not necessarily a drawback. Because automation is the development trend of the 4th Industrial Revolution.

SMT is not suitable for manual fabrication or low automation. In addition, the same goes for small or small investment capital. This is one reason why many through-hole mounting technologies are still being produced.

What Actually is Surface Mount Technology?

For a long time, the electronics industry good to use surface mounting components. This method did not have a worthy alternative for a long time, but new technologies have appeared.

Now SMT technology is actively good to use – this is the so-called surface smt pcb assembly installation, which has a number of advantages over the outdated one:
Reducing the cost of products
Similarly, improved component reliability
The dimensions of the mounted elements become smaller,
Subsequently, easier and faster installation,
Modern standards are met
In addition, the load on production capacity is reduced.

To perform surface mounting, a set of specific equipment is required. The list includes:
Devices for installing components on a printed circuit board.
Devices for applying and subsequent reflow of solder paste (solder).

Each of the devices is responsible for its function, and together they form a complete technological process.

Applying Paste or Solder during SMT PCB Assembly

There are two main ways to apply solder paste:
Dosing. Pneumatic dispensers are good to use, which can work without the use of specific stencils. That is, the device applies to boards of any size and configuration. The method has a significant drawback – the application speed is relatively small and depends on the skill of the person.

Printing through a stencil (metal or mesh). In this case, special devices are good to use that have a set of advantages:
Furthermore, able to handle a large area
Comes with a set of accessories,
Similarly, have a low cost.

Screen printing devices provide high productivity!

Component Mounting Devices

Hand-held manipulators are among affordable and easy-to-use surface mount devices. In constructive terms, these are quite complex devices, consisting of several elements:
The main unit equipped with the pantograph,
Vacuum pump (always built into the case) or compressor (located outside the machine),
Subsequently, head with a vacuum grip,
Several vacuum tips,
In addition, carousel feeder –
Responsible for the dosed supply of elements.

As options for manipulators, you can order additional equipment:
The hot air soldering system
Alternative types of feeders (from a canister or a tape),
Moreover, paste dispensers,
Process monitoring devices.

SMT vs THT – What is the Difference Between SMT and THT?

In the case of through-hole technology “THT” (THT – Through Hole Technology), the leads of embedded components insert into holes on the front (component) side of the printed circuit board to mount, and on the other side of the board (on soldering side), the leads of the parts are soldered. This soldering operation is done with a soldering iron working with a ‘solder wave’.

The disadvantage of through-hole technology is that the embedded part occupies both sides of the mounting plate.

Mounting using the “SMT – SMD” method:
In the case of the SMD device mounting technology on the board surface is, the SMT technology, the leads of the embedded components do not insert into the holes. They attach to the corresponding connecting points connections available on the board. As a result of which the leads of the parts are in direct contact with the so-called pads (‘pads’) made on the board.

Advantages of the Surface Mounting Method:
Eliminates the need for holes in the PCB
Greater cheapness of manufacturing processes, with their greater suitability for automation
Smaller component footprint and thus greater usability

SMT PCB Assembly Technology Options:
Pure surface mounting, in which only surface-mounted (“SMD”) devices are built into the board;
Single-sided surface mounting (“REFLOW”);
Double-sided surface mounting (“double REFLOW”);
Mixed mounting, in which both surface-mounted “SMD” devices and devices designed for traditional mounting (embedded through holes) are built into the board

The Difference between Surface Mount PCB and Through-Hole Technology PCB
When creating printed circuit boards, electronic components solder to the pads of a dielectric plate using the SMD or DIP method. SMD soldering is steadily replacing the DIP method of fixing elements every year. Types of surface mounting are conventionally divided based on the parameters and purpose of the chip components good to use:

SMD soldering of two-, three-, and four-pin elements;
Surface mounting of resistors, transistors, diodes, microcircuits, etc.
With this method of attaching components to the board, their leads are soldered to the surface of the dielectric plate, on which metalized electrically conductive circuits are applied. Solder paste is good to use to create contact between the element leads and the foil tracks.

It is a fine-grained sticky powder, which includes flux and solder. When heated, the paste becomes liquid. Its application to contact pads carries out mainly on special dosing machines.

smt pcb assembly method is increasingly replacing coated assembly, which is due to the pursuit of the miniaturization of components.

SMD components with flat housings, small dimensions, and special soldering tips can be mounted on the printed circuit board.

Through-Hole Technology PCB

In general terms, it differs little from the pairwise pressing method but has many significant differences in details. Same way, as in the case of the pairwise pressing method, cores are made on which the conductive pattern of the future inner layers of the MPP is made. However, the method of fabricating cores is purely subtractive; interlayer micro junctions between layers.

SMT vs SMD – What is the Difference Between SMT and SMD?

What is SMD?

SMD components are parts with contacts in the form of small legs or pads. Their small size allows them to come at a high density. In addition, SMD mounting allows you to fix components on both sides of the board.

The elements are soldered to pre-prepared pads. The technological process of surface mounting involves several stages. Strict adherence to technology at every step allows you to get a quality product.

In addition, there are at least two reasons that make it impossible to effectively use the through-hole metallization method for fabricating ultracomplex MCBs. The first reason is the use of microcircuits in BGA packages with small pin pitches. The second reason is the use of very large microcircuits (VLSI) in BGA, LGA, and similar packages with a very large number of pins. Let’s consider these cases in more detail.

Using Microchips in BGA Packages

When using microchips in BGA packages during smt pcb assemblywith a pin pitch of 0.60 mm or less, it becomes necessary to use vias with a very small diameter. For example, for chips with a ball pitch of 0.50 mm, it is necessary to use vias with a diameter of 0.10 mm. High-quality metallization of such micro-holes can be ensured only with a relatively small thickness.

Boards – 0.50–0.80 mm, no more. Such a limitation on the board thickness may not make it possible to fabricate an MCB with the required number of layers. In addition, the technological process of copper deposition in the channels through holes of such a small diameter often causes insurmountable technical difficulties to use by capillary effects inside such micro holes.

When good to use in the design of a VLSI device in BGA packages with the number of balls from 800 or more, for correct wiring, it becomes necessary to use a large number of layers (16 or more).

High Current Consumption in VLSI Power Circuits

The situation is aggravated in the case of high current consumption in VLSI power circuits and high power dissipation, and even more so if it is necessary to build matched transmission lines. In this case, it becomes necessary to use additional power supply layers, heat-removing layers, and shielding layers located between each pair of signal layers.

To strictly observe the impedance matching of the signal transmission lines, the distances between the signal and reference layers are regulated.

All this leads to the need to use a very large number of layers in the MPP, increase its thickness and increase the requirements for the accuracy of manufacturing elements of a printed pattern, as well as the accuracy of layer alignment and drilling accuracy.

As a result of the foregoing, the cost of manufacturing a printed circuit board increases significantly.

The Difference Between SMT and SMD

One of the most basic concepts regarding the difference between SMT and SMT is, smd is component that pcb manufacturers apply on printed circuit board whereas surface mounting technology refers to a method to apply those components on pcb board.

The SMT PCB Assembly Process
Each manufacturing plant will have its own process for the SMT technology line, but there are 4 general steps as follows:

Scanning solder alloy: Solder paste is a paste, that has high adhesion, and the composition will vary depending on the technology and the object to be welded. Solder paste is applied through the hole of a metal surface placed on the PCB to avoid unwanted adhesion to the surface.

Mounting chips and components: The machine automatically removes components from the conveyor belt and places them in the position where solder paste has been scanned. Then dry and flip the back to continue the mounting process. Smt pcb assembly technology is easy to improve to 2-sided mounting at the same time.

Heating – cooling: At the drying stage, the PCB goes through areas of gradually increasing temperature for the components to adapt, avoiding sudden damage. When the solder paste melts, the components will glue to the PCB. Next, the components will get cleaning with chemicals and solvents and then quickly dry with compressed air.

Error checking: Optical or X-ray machines will develop defects in components.

What is Your SMT PCB Cost and Price?

The PCB Assembly Price Including:
Setup fee: $8.00Stencil: $1.50SMT Assembly: $0.0017 per jointHand-soldering labor fee: $3.5
Manual Assembly: $0.0173 per joint

Components cost: Based on the components you choose for assembly

SMT Assembly FAQs
What does your quoted price include?

The pcb assembly price includes:
$8.00
Stencil: $1.50
SMT Assembly: $0.0017 per joint
Hand-Soldering labor fee: $3.5
Manual Assembly: $0.0173 per joint
Component Cost: Based on the components you choose for assembly
Our online quotes will show the exact assembly fee and component cost after you select the parts for assembly

NextPCB: Custom SMT PCB and Assembly Manufacturer

Fixing SMD components during smt pcb assemblyrequires engineering knowledge and practical skills. Moreover, the chips are extremely sensitive to overheating and come with small outputs. Therefore, fastening with an ordinary soldering iron often leads to their destruction. Without special equipment, mass production is difficult to establish.

By contacting Nextpcb, you can order the manufacture of SMD microcircuits with a guaranteed result. We produce boards in strict accordance with the technical specifications, check the performance of the product with sensitive testers, and fulfill orders, individually approaching each client.

Conclusion

In recent years, smt pcb assembly has become the mainstream for board mounting due to the progress in miniaturization and high density of boards. When using both the SMT process and the IMT process for some products, the SMT process is usually completed first before entering the IMT stage.

Due to market demands and increasing labor costs, IMT is about to replace by SMT. The SMT process is mostly common in fields that require portability, such as mobile phones, PDAs, and GPS. For some products that use high voltage and large current, the percentage of SMD adoption is low due to special parts.

Article source: Design news

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