Guideline

PCB Surface Finishes: Best Practices for Ensuring Quality and Longevity

PCB Surface Finishes

Nowadays, PCBs are considered the backbone of modern electronics and the surface finish is one of the crucial parts of their performance, reliability and durability. Selecting the best PCB surface finish depends on the quality and longevity of the PCB and adhering to these are the best practices in the design process flow.

What Are PCB Surface Finishes

PCB surface finishes are also called PCB surface treatment.  They are thin layers of metal or organic protection layers applied on the PCB pads, to protect the copper pads from oxidation or contamination, and also enhance the solderability in the PCB assembly process

There are different kinds of surfaces according to the technologies, cost and usage. The most commonly used PCB surface finishes are: HASL, ENIG, ENEPIG, immersion tin, immersion silver, OSP, plating gold, and carbon ink. 

PCB Surface Finishes OSP

PCB Surface Finishes Comparisons

PCB surface finish is one of the crucial steps that establish the connection between the exposed bare copper on the board and the components that will be assembled on it. It protects the copper from oxidation and also prepares the surface of the board for soldering components.

There are 2 major types of surface finish:

  • Metallic surface finish
  • Organic surface finish

HASL, ENIG, ENEPIG, and IMMERSION TIN belong to metallic finish while OSP and CARBON INK belong to organic finish.

Each finish has its advantages and disadvantages depending on the applications where they are being used. See the table below to distinguish between the surface finishes:

Metallic Surface Finish Comparison Table:

Surface finishAdvantagesDisadvantages
HASL
  • Cost effective
  • Robustness
  • Widely used
  • Solderability is good
  • Uneven surface
  • Shelf-life concerns
  • Not suitable for fine pitch component
  • Not recommended for harsh environments
  • Contains LEAD
      ENIG
  • Flat surface
  • Excellent solderability
  • Lead free process
  • Resistance to oxidation
  • Longer shelf life
  • Cost is high
  • Brittle due to gold
  • Black pad defect
  • Not suitable for aluminium wire bonding
  • Complex due to multiple processes
ENEPIG
  • Excellent flat surface
  • Lead free & ROHS compliant
  • Extended shelf life
  • Enhanced wire bonding capability including aluminium wire bond
  • Cost is very high
  • Process complexity
  • Not available widely with all PCB manufacturers
IMMERSION GOLD
  • Flat surface
  • Excellent solderability
  • Lead free process
  • Resistance to oxidation
  • Cost is high
  • Brittle due to gold
  • Black pad defect
  • Not suitable for aluminium wire bonding

Complex due to multiple processes

 

Organic Surface Finish Comparison Table:

Surface finishAdvantagesDisadvantages
ORGANIC SOLDERABILITY PRESERVATIVE

(OSP)

  • Less expensive than carbon ink
  • Lead-free & ROHS compliant
  • Widely available
  • Limited shelf life
  • Moderate solderability
  • Not suitable for HDI boards
CARBON INK
  • Slightly expensive compared to OSP
  • Lead-free & ROHS compliant
  • Longer shelf life
  • Good solderability
  • Cost is higher than OSP
  • Limited availability

 

How to Select PCB Surface Finish to Ensure Quality and Longevity

Overall, the Selection of PCB surface finish depends on several factors. A few of them are listed below:

  • Number of solder cycles 
  • ROHS requirement
  • Application usage
  • Environmental condition
  • Cost constraints
  • Assembly process
  • Density of components
  • Shelf life of the board
  • Wire bonding capability
  • Surface flatness

PCB Surface Finishes Plating Gold

Now we know the different kinds of surfaces and also the factors to select PCB surface finishes. So let us explore the best practices to consider for PCB surface finish to have better quality and longevity in different environments. 

1. Choosing the right surface finish

It is vital to select the right surface finish for a specific application before diving into best practices. Consideration should be given to factors like solderability, uniformity, resistance to oxidation, compatibility with assembly processes and environmental conditions.

2. Following Manufacturer guidelines

Each manufacturers have their own set of guidelines for handling, storing and manufacturing the boards due to multiple processes involved in the floor. To avoid quality issues and errors, one has to follow the suggested handling duration, the number of immersion cycles, chemical concentration and temperature conditions, while selecting the right surface finish.

3. Implementing quality control measures

Implementing proper quality control measures at each stage of the PCB manufacturing process is important. Right from inspecting the incoming material, plating thickness, performing solderability tests and conducting visual inspection are necessary to identify the defective products and to maintain the quality of the board.

4. Minimize contamination and handle

PCBs that are prone to contamination after the surface finish is done. To avoid such contamination and damage to the surface, handling PCB after surface treatment is very crucial. Use clean tools, wear gloves, and avoid making contact with the surface finish when handling the boards. PCBs should be kept in protective packaging to prevent mechanical damage, moisture, and environmental pollutants.

5. Perform Reliability test

In the real world, reliability testing is required to confirm the functionality and durability of the PCB surface finish. This test includes heat cycling, accelerated ageing test and environmental stress test to evaluate the surface finish endurance.

6. Ensure compliance with standards

Make sure that PCB surface finishes meet customer specifications, regulations, and industry standards. Check for compliance with standards including RoHS for environmental laws, IPC-610 for solderability, and IPC-4552 for ENIG. Embracing the standards offers uniformity, and excellent quality and will be aligned with the expectations of end-user requirements.

7. Continuous process improvement

Based on the user feedback, quality and development in the industry process, continuous improvements have to be done in the process to stay in line with the market standards. Regular process optimization, conducting training programs and upgrading the equipment helps to stay ahead of market trends and meet customer expectations.

In summary, by adhering to these recommended techniques PCB manufacturers can ensure the quality, durability and longevity of surface finish. Investing in the quality control process, upgrading equipment and optimizing the process is essential to achieve superior PCB surface finishes.

 

Summary

In general, it is quite necessary for PCB designers and PCB fabricators to know that selecting the right PCB surface finishes is crucial for ensuring optimal PCB performance and the reliability of any electronic applications. Each surface finish has its advantages and disadvantages. Depending on the kind of application and the kind of environment where the boards are used, considerations have to be done carefully. Considerations can be made on several factors such as the kind of environment the board is used, cost-effectiveness, reliability, durability and environmental compliance. Selection of a suitable surface finish is very vital in today’s rapidly growing electronic industry.

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