Posted:05:20 PM December 06,
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writer: NextPCB
Hot air solder leveling and lead-free HASL (Hot Air Solder Leveling) are the two prominent surface finishes in the PCB Manufacturing and Assembly Process. However, there is a noticeable difference; Lead-Free HASL does not use tin and lead solder.
Yet, when choosing the right surface finish for your circuit boards, it is vital to choose a cost-effective and RoHS-compliant surface finish. Suppose you want to use HASL as your surface finish choice and need help deciding which surface finish to use. In that case, this guide examines the pros and cons differences between HASL and lead-free HASL.
Surface Finish is metalizing the outer layer of a PCB being soldered. The function of PCB surface finish is to offer protection against corrosion on the copper circuitry. Also, it fosters easy soldering of circuit board components.
There are varied kinds of surface finishes employed in the PCB Industry. They are: Hot Air Solder Leveling (HASL), Electroless Nickel/Immersion Gold (ENIG), Immersion Silver (ImAg), Organic Solderability Preservative (OSP), and Immersion Tin (ImSn)
Hot air solder leveling (HASL) is the least expensive PCB surface finish. Many PCB Manufacturers commonly use this surface finish as it is economical and widely available. When applying Hot Air Surface Leveling on circuit boards, the board is dipped in molten solder and then scrapped off with a hot air knife.
PCB Manufacturers that employ through-hole technology or larger surface mount technology designs, hot air surface leveling excels in these designs. For smaller boards, it is not ideal. Also, The solder used is typically Tin-Lead solder, making it RoHS non-compliant.
Lead-free hot air solder leveling is a type of surface finish that employs lead-free solder alloys. Instead of the conventional Tin-Lead eutectic alloys used by HASL, Lead-free HASL employs other solder alloys that do not contain lead.
When applying Lead-free HASL on the circuit board, molten solder is first used on the circuit board to achieve wetting. Then, air knives (usually set at a temperature above the lead-free solder melting point) are used to scrap off excess solder.
After the solder has solidified, the circuit board is passed through the washer, where solder flux residues are removed.
Despite being considered an environmental alternative to the standard HASL, lead-free HASL is least employed in surface finishes. The reason is that other innovative surface finishes are available in the PCB market. They include OSP and ENIG.
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Many Customers understand the HASL process. Still, they need to learn the difference between HASL and Lead-free HASL. However, the differences between them are:
Choosing the proper surface finishing during PCB production is essential. This careful consideration is because PCBs are found in every electronic component worldwide, ranging from colossal industrial engines to children's toys.
Hence, PCB production is taken seriously to avoid exposing toxic materials such as lead to children and adults, which could adversely affect their health. Hence, since EU RoHS's inception in , HASL has taken on a new approach by not utilizing lead in its surface finishes.
Hot Air Surface Leveling (HASL) application in surface finishing is a common trend in the PCB industry. This guide has provided differences between HASL and lead-free HASL as they provide respective physical and mechanical strengths in their application.
Also, while HASL offers cost-effective benefits to PCB surface finishes, it is not RoHS compliant. As a result, should ensure high safety upon application of these finishes.
Choosing the surface finish is an essential step in the design of your printed circuit boards.
The PCB surface finish helps protect copper circuitry from corrosion. It also provides a solderable surface for your components. There are a number of factors to consider, including:
Below are 5 types of PCB surface finishes, along with their benefits and drawbacks.
'Hot Air Solder Leveling' is the least expensive type of PCB surface finish.
It is widely available and very economical. The board is dipped in molten solder and then leveled off with a hot air knife. If you're using through-hole or larger SMT components, HASL can work well. However, if your board will have SMT components smaller than or SOIC, it is not ideal.
If you are looking for more details, kindly visit lead-free hasl.
The surface is not completely level, so this can cause issues with small components. The solder used is typically Tin-Lead. That means that it isn't RoHS compliant. And if reducing the amount of lead you use is important, you may want to choose Lead-Free HASL instead.
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Lead-Free HASL is similar to standard HASL, but with an obvious difference' It doesn't use Tin-Lead solder.
Instead, Tin-Copper, Tin-Nickel or Tin-Copper-Nickel Germanium may be used. This makes Lead-Free HASL an economical and RoHS compliant choice. But like standard HASL it is not ideal for smaller components.
For boards with smaller components, immersion coatings can be a better choice. They are slightly more expensive but more suitable for this purpose.
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Disadvantages:
With all immersion coatings, a chemical process is used.
A flat layer of metal is deposited on the copper traces. The flatness of the coating makes it ideal for small components. Tin is the least expensive type of immersion coating. Although it is an economical choice, it comes with some drawbacks.
The main drawback is that after the tin is deposited onto the copper it begins to tarnish. That means that if you want to avoid lower quality solder joints, you need to do your soldering within 30 days.
If you are expecting a high volume of production this may not be an issue. And if you are using large batches of boards quickly, you can avoid tarnishing. However, if your production volume isn't high, it may be better to choose a coating like immersion silver.
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Immersion silver does not react with copper the way that tin does. However, it does tarnish when exposed to air.
That means it needs to be stored in anti-tarnish packaging.
When stored in proper packaging it will still be solderable for 6-12 months. But once the PCB is removed from its packaging, it will need to go through solder reflow within a day. A higher shelf life can be achieved with gold plating.
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Electro gold flash plating consists of a thin layer of gold over electroless or electrolytic nickel.
This type of plating is hard and durable. It also has a long shelf life, lasting for years. However, its durability and shelf life make it more expensive than any of the finishes mentioned above.
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Remember that when choosing the finish for your PCBs, you need to consider component types and production volume. You'll also need to consider requirements for durability, environmental impact, and cost. By taking all these factors into consideration, you can be sure to make the right choice.
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