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PCB for SMT (Surface Mount Technology)

Detailed Explanation of PCB for SMT or Printed Circuit Board (PCB) for Surface Mount Technology (SMT).

PCB for SMT or Printed Circuit Board (PCB) for Surface Mount Technology (SMT) must consider factors like CTE, cost, dielectric properties and Tg. Let us understand in Detail.

What is a PCB?

A Printed Circuit Board, or PCB, is an integral part of Electronics. A PCB is basically a substrate (normally made from glass epoxy or other PCB Material) with conductive traces etched from copper sheets. These copper traces facilitate flow of electricity. Thru-Hole or SMD Electronic components or a Mix of Both are soldered along this conductive pathway thus controlling the flow and quantity of electricity needed.

A Printed Circuit Board is also known as Printed Wiring Board (PWB). When all the electronic components are soldered on a PCB, it is called a PCB Assembly or PCA and sometimes PCBA (Printed Circuit Board Assembly).

SMT PCB

SMT PCB

PCB for SMT – Printed Circuit Board (PCB) for Surface Mount Technology (SMT)

Printed Circuit Board (PCB) for Surface Mount Technology (SMT) need to be chosen wisely taking into consideration factors such as CTE (Coefficient of Thermal Expansion), cost, dielectric properties and Tg.

When designing surface mounting board (PCB), the selection of PCB Material is basically determined by the type of SMD components to be used. In any Electronics manufacturing or PCB Assembly Company, when leadless ceramic chip carriers (LCCC) are mounted on printed circuit boards made out of glass epoxy substrates, solder joints cracking is generally seen about 100 cycles. The cause of the excessive stress is the CTE differential between the ceramic package and the glass epoxy substrate.

Problems Caused by Wrong Selection of PCB for SMT

Wrong selection of PCB for SMT can lead to solder joint cracking problems.

There are three different approaches to solder joint cracking problems:

  1. Using a substrate with a compatible CTE;
  2. Using a compliant top layer substrate; and
  3. Replacing leadless ceramic packages with leaded ones.

The most widely used substrate for SMT Printed Circuit Boards, is glass epoxy. It entails no CTE compatibility problems when used for plastic surface mount packages. However, this provides the solution for commercial applications only.

The most commonly used substrate for PCBs for military applications is one with a CTE value compatible with that of the ceramic packages that has been specified. Each PCB substrate option has its own advantages and disadvantages. Designers need to be carefully balances the constraints of cost with reliability and performance needs. In addition, solder masks and via hole sizes should be selected carefully.

SMT PCB Assembly Process

FAQs: SMT PCB

SMT involves mounting components directly onto the PCB surface, whereas through-hole technology involves inserting components with wire leads through holes drilled in the PCB. SMT is more space-efficient, allows for automated assembly, and is suitable for high-volume production, while through-hole technology offers better mechanical strength for heavy components.

SMT PCBs offer several advantages, including smaller form factors, higher component density, reduced manufacturing costs due to automated assembly, improved electrical performance due to shorter interconnections, and better signal integrity. They are also more suitable for miniaturized and portable devices.

The assembly process for SMT PCBs involves applying solder paste to the board, placing surface-mount components on the paste, and then subjecting the board to a reflow soldering process. During reflow soldering, the solder paste melts, creating a strong electrical connection between the components and the PCB. This process is typically automated using pick-and-place machines and reflow ovens.

While SMT offers many benefits, it also presents challenges such as precise alignment of small components, risk of tombstoning (where one end of a component lifts during soldering), and susceptibility to solder joint defects due to thermal stresses. Careful design, accurate stencil printing, proper component handling, and quality control measures are essential to overcome these challenges.

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Santosh Das

Santosh, founder of this Electronics Tutorial Website, is an Electronics Geek, Blogger and Young Entrepreneur. He possesses vast experience in the field of electronics, electronic components, PCB, Soldering, SMT, Telecommunication, ESD Safety, and PCB Assembly Tools, Equipment and Consumables. Keep visiting for daily dose of Tips and Tutorials.

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20 Responses

  1. soldertraining says:

    A Printed Circuit Board is also known as Printed Wiring Board. The most widely used substrate for SMT Printed Circuit Boards, is glass epoxy. Nice Post. Thanks for sharing.

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