Why it is Important to Choose ENIG Surface Finish?
Did you ever hear about surface finishes in PCBs? No! don’t worry, we are here to give all information about the surface mount technology. Moreover, we will describe you that how ENIG immersion gold surface finish is better in comparison to several other technologies.
What is Immersion Gold
Immersion gold (ENIG) is the chemical deposition of a gold layer on a nickel sublayer. One of the main alternatives to HASL technology. It is a top coat of the Ni / Au family (Immersion Gold + Electroless Nickel). The basic thickness of the gold layer is 0.05-0.1 microns, nickel is 3-7 microns. The material meets all the mandatory requirements of the EU RoHS directive.
Benefits of Using
- Immersion gold is a safe, lead-free finish.
- Allows additional in-circuit testing.
- Create perfectly flat, smooth pads.
- Provides good solderability and high surface conductivity.
- The material is durable – the average shelf life is 6 months. Not susceptible to ionic contamination, does not oxidize.
- It can be applied to components with a small pitch (0.4-0.5 mm), using various types of soldering (including multiple ones) and mounting methods (for example, bonding crystals).
As you know that PCB boards have become an integral part of all electronic devices: nowadays we can’t imagine any device without these circuit boards. However, it is very essential to select best materials and technologies for ideal performances of PCBs.
Hence, for better performance, PCBs need to endure the rigors of several distinct hard operational environments. So, designers coat the PCB boards with surface finishes of different kinds. People who involve to the PCB board industry can understand the importance of PCB surface finishes.
Basically, all PCB boards have several types of copper finishes on their surface. Furthermore, this surface finish is really important and essential for ideal performances. So, here we will learn what is surface finish and all the different kinds of surface finishes. Moreover, all the beneficial qualities of ENIG immersion gold surface finish.
What is Surface Finish in PCB?
A surface finish in a PCB is actually the metal coating between a component and the bare PCB board. All PCB boards consist a special layer of copper that oxidizes in the condition when it enters with the air. In fact, air and other environmental conditions can reduce the oxidizing.
But if you will not protect the PCBs properly these copper layers will deteriorate and oxidize. Hence, your PCB boards will become unusable. So, for securing the PCB functionality, surface finish has really important. The basic and crucial purposes for finishes are:
- Manufacturers use surface finish in order to protect circuitry and copper surface
- It is helpful in order to prepare surface for soldering related components in assembly
The process is multi-stage. First, the printed circuit boards undergo a primary treatment during which the surfaces are activated. Then, a layer of chemical nickel (3-7 microns thick) is deposited. With the help of an exchange reaction, a 0.05-0.2 micron layer of gold is restored.
The main function of gold is to protect nickel from possible oxidation, while the nickel itself effectively prevents copper / gold diffusion. All coating processes take place in a special temperature regime.
Why it is Important to Choose Best Surface Finish?
Printed Circuit Boards are actually responsible for connecting and loading all essential electronic components in the electronic equipment. These electronic components are necessary in order to implement electronic circuit function.
The best performances of your electronic appliances totally depend on the functionality of PCB boards. So, it is essential to choose ideal surface finishes for better performances. For ideal PCB Assembly electric connection between circuit and components must be perfect. Furthermore, it all and all depends on the type of metal which you select for surface finishes.
The perfect surface finish creates a crucial and critical interface between the PCB and the components.
What are Important Considerations for PCB Surface Finish?
It is really important to select surface finish to use in manufacturing the PCB boards. You have to use the perfect material for surface finishes which suits your needs and requirements. Because best material will help you to ideal construction of electronic assembly for your PCBs.
Additionally, it is a crucial step to choose ideal surface finish for ideal functioning of our PCBs in any electronic device. Basically, PCB surface finish supports in order to protect copper circuitry from corrosion and many other defects.
Furthermore, it also has ability to provide best solderable surface for components. But there are several considerations which you must follow for 100% best surface finishes. And these are:
- The types of components which you make use
- Production volume that you have decide to produce
- Your necessities for durability and strength
- Impact of the environmental
- Last but really important, the overall cost.
Generally, there are many kinds of PCB surface finishes which are available in the market. Each type has its own value and benefits. Moreover, they also have some disadvantages. We are going to tell you the names of 7 different types of surface finishes. Such as:
- Hot Air Solder Leveling (HASL)
- Lead-free HASL
- Electroless Nickel Immersion Gold (ENIG)
- Immersion Silver (IAG)
- Nickel Palladium (ENEPIG)
- Organic Solderability Preservative (OSP)
- Immersion Tin (ISN)
Actually, the surface finishes have great influence on the,
- Reliability of the resulted products.
Moreover, there are basically half of a dozen or more than it, common kinds of surface finishes. Moreover, it is a fact that all the above 7 kinds of the surface finishes have their own importance. But here we are concentrating on very important and beneficial immersion gold surface finish or ENIG immersion gold surface finish.
The thin layer of immersion gold protects the copper from corrosion on the surface of PCB board. Additionally, it has a best soldering for the copper. ENIG immersion gold surface finish is indeed
a RoHS complaint surface finish. Hence, it provides more reliable,
- Solder joints
- A planar surface.
Moreover, it is extremely resistant to,
- Various environmental storage conditions and many more.
Due to the implementation and growth of RoHs regulation, ENIG has become the most widely used finish in the industry of PCB.
What is the Typical Thickness of Gold in ENIG Immersion Gold Surface Finish?
Basically, in ENIG the layer of gold has generated on the layer of nickel via displacement. This process continues till the layer of gold which has generated is fully covered with nickel. So, it is the reason that why PCB designers use thin layer of gold in ENIG immersion gold surface finish. This thin layer of gold truly provides protection to the nickel from rust and oxidation.
Furthermore, the typical thickness generally ranges from 0.05 – 0 23 µm (2 – 9 µ in) gold over 2.5 – 5.0 µm (100 – 200 µ in) nickel. In fact, this typical thickness always remnant consistent in every part of the PCB.
What are the Advantages of ENIG Immersion Gold Surface Finish?
One of the best advantages of EMIG is, it is actually a perfect choice for modern and next generation. Because it is an ideal choice for complex surface components. Additionally, it includes flip chips and BGAs. In fact, many other surface finishes have many limitations for applying in the new and complex PCB boards.
Furthermore, this kind of plating is extremely hard, strong and durable. ENIG immersion gold surface finish can last for many years as it has a long shelf life. However, both of these advantages have made it very expensive in comparison to the other surface finishes.
Even though, EMIG (Electroless nickel immersion gold) surface is expensive technology of finishing. But it is extremely famous for the several ideal reasons.
These Reasons are:
- ENIG meets and complies with all the requirements of RoHS.
- The gold layer can provide several benefits. Such as,
- High strength
- Low contact resistance
- Very few chances of oxidation.
All These Features Help in order to Meet Circuit Conductivity Needs.
- ENIG immersion gold surface finish has ability to protect copper and nickel layers from oxidation. So, all these attributes play an important role in an excellent solderability.
- ENIG also consists some best chemical properties. These chemical properties have provided by layers of gold and nickel. These layers are,
- Impressive wettability
- Surface planarity.
ENIG immersion gold surface finish is also extremely popular for its electrical testability.
- Electronic designers are making use of PCBs which has created by using ENIG surface finish in,
- Latest smartphones
- Automotive electronics
Possible way for the ENIG colored surface to appear:
- Manufacturing defects associated with aging of the electrolyte. The surface becomes undulating for component mounting. This path refers more to low-quality metallization.
- The gilding may not be thick enough. The redox reaction in water can lead to an undesirable increase in the thickness of the nickel oxide.
- Exposing boards after rinsing in a freestanding oven can easily cause oxidation of the ENIG surface.
- If the gilding is too thin or uneven, the possible diffusion of water or chemicals to the nickel surface leads to oxidation.
- Low phosphorus content in the nickel layer. Phosphorus in nickel prevents corrosion. Flushing can accelerate nickel corrosion. In this case, a standard assessment should be made for low phosphorus or blackness of the site.
- The ENIG layer sometimes reacts with chlorides (from the flux) in higher cleaner formulations, resulting in oxidation, such as a black area oxidation reaction.
Troubleshooting ENIG Surface
- Conduct a standard ENIGsurface assessmentfor low or high phosphorus content:
- A) in the nickel layer;
- B) between gold and nickel.
High phosphorus content leads to nickel oxide.
- Monitor the formation of nickel oxide on each layer of ENIGusing:
- A) Auger electron spectroscopy and look at the behavior of nitrogen and oxygen;
- B) Transmission electron microscopy and look at nitrogen oxide layers or secondary, ionic, mass spectroscopy for nitrogen behavior;
- B) Sequential electrochemical reduction analysis to assess the presence of oxides and intermetallic layer.
- Look for improved results when using oxygen or hydrogen plasma. If oxygen is better, then the reason is related to organic pollution. If hydrogen helps, then the problem is more in the oxidation reaction.
What are Some Limitations of ENIG Immersion Gold Surface Finish?
Although ENIG immersion gold surface finish has several advantages for best functionality of your PCBs. But it also has some limitations. And these are:
- This surface finishes are expensive.
- ENIG has black pad syndrome.
- Its huge drawback is that it is not good for reworking.
- This surface finish is damage from ET.
- It also has signal Loss (RF).
- ENIG in fact has complex process.
Which Surface Finish will be Best for your products?
As we have described many advantages of ENIG. Moreover, it is extremely good choice for your PCBs. But you have to remember that while you are selecting the surface finishes you have to consider,
- Best surface finish for your production volume.
- Perfect surface finish for the kind of your production.
Furthermore, you should consider that which kind of surface finish will perfectly suit your environmental conditions. You have to take care that surface finish must be durable for your production needs.
Hence, when you pay full and deep attention to these considerations your PCB production will be perfect. Moreover, it will also make you 100% sure about the ideal functionality of your electronic appliances. In fact, ENIG immersion gold surface finish is expensive but it suits all your needs and demands that you want for better surface finishes.
PCBMay could provide many kinds of surface finishes,so when you have any inquiry,please send it to email@example.com.