Surface Mount Design Considerations in SMT & CTE Mismatching
Surface Mount Design issues, CTE Mismatch Problem and Land Pattern Standard must be settled before a SMT design or packaging direction is selected.
Surface Mount Design issues, CTE Mismatch Problem and Land Pattern Standard must be settled before a surface mount technology design or packaging direction is selected.
Table of Contents:
Guidelines & Standards to Consider in Surface Mount Design
- System analysts start with determining product needs in the marketplace. Therefore, the designer must look at the proposed product from the systems point of view. Great devices on printed circuit boards do not sell in the marketplace. Products sell. Therefore, the designer must consider market needs, function, and package moisture sensitivity. The product must also satisfy thermal and solder joints reliability requirements. As the packaging density increases, moreover, thermal problems are compounded, with a potential adverse impact on overall product reliability.
- Solder joint reliability for surface mount technology is a source of concern because of CTE mismatch, between ceramic packages and PCB for SMT made from FR-4 glass epoxy PCB Material.
- Because the plastic packages used in commercial applications have complaint leads, they do not experience problems related to CTE mismatch. The large plastic packages, especially plastic ball grid arrays (PBGA), may be prone to cracking at reflow soldering temperatures, however, and this is an industry problem. Long-term solutions are still evolving, but baking before reflow soldering offers one answer.
- The increase in SMD Electronic Components package density on board has necessitated the use of file lines at closer spacings. This can increase cross-talk between the lines, especially if they carry high speed signal.
- The product design is also influenced by the type of CAD system that is available. The cost or the schedule or both may be affected by the type of CAD system used for SMT PCB design.
Conclusion
Thus, for every SMT board, the designer must consider all the pros and cons of designing the board in SMT. If the decision is to go ahead with SMT, then it is important to follow the specific guidelines and rules.
FAQs: SMT Design Considerations
How do I choose the right component placement for surface mount design?
Proper component placement involves arranging SMT components on the PCB to optimize signal paths, reduce noise, and ensure efficient manufacturing. Place critical components first, group similar components, minimize trace lengths, and follow manufacturer's recommendations for spacing and orientation.
What is thermal management’s role in surface mount design?
Thermal management in surface mount design prevents components from overheating. Consider factors such as component power dissipation, copper trace widths, vias for heat dissipation, and placement near heat sinks or thermal reliefs to ensure optimal heat distribution and dissipation.
How does surface mount design impact signal integrity?
Surface mount design can affect signal integrity due to trace routing, component placement, and parasitic effects. To maintain signal integrity, adhere to controlled impedance for high-speed signals, avoid crossing split planes, and minimize trace lengths to reduce signal degradation and electromagnetic interference.
What are the best practices for manufacturability in surface mount design?
Design for manufacturability involves creating PCB layouts that are easy and cost-effective to produce. Use standard footprints and component sizes, maintain proper solder mask and silk screen clearances, ensure adequate spacing between components, and follow industry guidelines to minimize assembly errors and reduce production costs.
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[…] where hermiticity is not required. The ceramic packages have solder joint cracking due to CTE mismatch between the package and the substrate, but the plastic packages are also not trouble […]
[…] CTE (Coefficient of Thermal Expansion): The ratio of the change in dimensions to a unit change in temperature. CTE is commonly expressed in ppm/ degree Celsius. […]
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