The process requirements in the PCB production are very important, which directly determines the quality and positioning of a board. Such as HASL, gold plating pcb , ENIG.
For more information, please visit lead-free hasl.
Due to the good quality of ENIG, the price is higher too. Many customers choose the most common HASL process.
1. On the surface, Lead-tin is brighter and lead-free tin (SAC) is dim.
2. Lead in HASL is harmful to humans, but lead-free not. The lead eutectic temperature is lower than lead-free, which depend on Lead-free alloy composition. For example, The eutectic of SNAGCU is 217 degrees, the pcb soldering temperature is eutectic temperature plus 30 to 50 degrees. The lead eutectic is 183 degrees. The mechanical strength and brightness with lead is better than lead-free.
3. The Lead content in HASL-LF is not more than 0.5, while HASL has a lead of 37.
4. The lead will increase the activity of the tin wire during the welding process, so Lead wire is easier to use than lead-free wire. However, lead is toxic and not good for the human body. What is more, Lead-free tin will have a higher melting point than lead-tin, so the solder joint is much stronger.
In printed circuit board (PCB) manufacturing, a protective and conductive coating is applied on the copper traces to facilitate soldering of components. The two most common solder coatings are Hot Air Solder Leveling (HASL) using tin-lead solder alloys and Lead-free HASL using tin-based lead-free alloys. This article provides a detailed comparison between traditional leaded HASL and modern lead-free HASL processes.
The Hot Air Solder Leveling (HASL) process deposits a thin solder coating on the PCB conductors to protect them from oxidation and provide a solderable surface. The key steps are:
This coats the exposed copper traces with a smooth solder layer ready for component assembly. Lead-tin alloys like Sn63/Pb37 used to be common for HASL but environmental concerns over lead has led to a transition to lead-free solders.
Traditional HASL used tin-lead solder alloys containing 30-40% lead to coat PCBs. The most common composition was 63% tin (Sn) and 37% lead (Pb) or Sn63/Pb37:
However, lead is a toxic heavy metal banned under RoHS. This prompted a shift to lead-free HASL processes using tin-based solders.
Lead-free HASL eliminates lead and uses greener tin-based solder alloys. The main options are:
1. Pure Tin (Sn100)
2. Tin-Copper (SnCu)
3. Tin-Silver-Copper (SAC305)
4. Tin-Bismuth (SnBi)
Among these, SnCu and SAC alloys are most popular for lead-free HASL. The specific alloy is selected based on soldering process needs and costs.
Lead-free HASL coatings are typically thinner than traditional leaded HASL:
Thinner coatings are used to conserve higher priced lead-free solders and account for their higher hardness. Thick leaded deposits tend to crack and warp under board flexure.
Switching from leaded to lead-free HASL requires optimizing the soldering process:
With the right parameters, the lead-free HASL process can match leaded HASL for solderability and surface finishes.
There are three main equipment configurations used for lead-free HASL processes:
1. Pumped Molten Solder
2. Foam/Spray Flux + Static Solder Pot
3. Selective Deposition
Each has its own pros and cons. The method is selected based on production environments, volumes, and flexibility needs.
The properties of traditional leaded HASL versus lead-free HASL are compared below:
PropertyLeaded HASLLead-Free HASLSolder AlloyTin-Lead (SnPb)Tin-Copper (SnCu), SACLead Content30-40%<0.1%Melting Temperature183°C217-232°CSolder Bath Temperature200-210°C240-255°CCoating Thickness100-300 μin (2.5-7.5 μm)50-100 μin (1.25-2.5 μm)WettabilityGoodModerate to GoodSolderabilityExcellentGood to ExcellentDuctility/HardnessDuctile/SoftHarder/More BrittleCorrosion ResistanceModerateGoodLeach ResistanceModerateBetterCreep ResistanceModerateBetterFatigue ResistanceModerateGoodDrop/Shock ResistanceGoodModerateWhiskeringNoMinor risk (mitigated)CostLowerHigherSome key advantages and disadvantages of switching to lead-free HASL are:
For acceptable reliability some important factors to consider are:
With optimal processing, lead-free HASL can achieve the adhesion, solderability, and reliability needed for most applications.
The electronics industry has widely adopted lead-free HASL surface finishes to meet environmental regulations and market demands. While the switch from conventional SnPb involves process changes and cost impacts, lead-free coatings offer important advantages. With proper control of materials, fluxes, temperatures and equipment parameters, high quality and reliable lead-free HASL coatings can be achieved. The process continues to evolve with newer solder alloys and selective deposition methods for further improvements.
The popular lead-free HASL alloys are pure Tin (Sn100), Tin-Copper (SnCu), Tin-Silver-Copper (SAC305/405), and Tin-Bismuth (SnBi). SnCu and SAC305 are most common allowing better wetting, strength and whisker resistance than pure Tin.
Lead-free HASL deposits are typically 50-100 microinches thick versus 100-300 microinches for leaded HASL. Thinner coatings conserve costlier lead-free solders and prevent cracking issues seen with thick lead-free layers.
Organic Solderability Preservatives (OSPs) and Immersion Silver provide excellent solderability under lead-free or no-lead HASL. Other options like ENIG, Immersion Tin, and Immersion Gold also work well.
To suit the higher 227-240°C melting point of SnCu alloys, the solder pot temperature needs to be maintained between 245-255°C, compared to 200-210°C used for leaded SnPb solders.
Jet printing selectively sprays lead-free solder using drop-on-demand inkjet heads only onto required areas. Another method uses laser-cut stencils allowing solder paste application just on exposed traces. Both dramatically reduce solder usage.
PCB surface finish is a metal or organic coating on PCB pads that protects the copper and boosts solderability. Lead-free HASL (hot air solder leveling) is the most common PCB surface finish, and if you don't specify which surface finish you want, we assume you want lead-free HASL for your boards.
However, lead-free HASL is not allowed for flexible PCBs and rigid PCBs with a thickness smaller than 0.5mm. You have to replace it with ENIG (electroless nickel immersion gold) or OSP (organic solderability preservatives). This article reveals HASL and ENIG and compares them.
HASL means using tin/lead solder to spray the PCB pads and then using hot air to blow the PCB surface so that the pad surface is level. The thickness of HASL is 1mil to 2mil (25.4μm to 50.8μm, or 0.025mm to 0.05mm).
HASL is a cheap PCB surface finish. And its solderability is good.
However, HASL doesn't meet the lead-free requirements in most of the world, and in most cases, we use lead-free HASL.
The properties of lead-free HASL are pure tin. The thickness of lead-free HASL is 0.1mil to 1mil (2.54μm to 25.4μm, or 0.mm to 0.025mm).
Lead-free HASL is the default surface finish from the PCB manufacturer PCBONLINE. Compared with HASL, PCB pads with lead-free HASL look dim, and the soldering temperatures are higher.
HASL
Lead-free HASL
Properties
Tin and lead (37% of lead)
Tin (lead less than 0.5%)
PCB pad finish
Want more information on multilayer pcb design tips? Feel free to contact us.
Glossy
Dim
Solderability
Good
A little worse than HASL
Reflow soldering temperatures
210&#; to 245&#;
240&#; to 270&#;
Wave soldering temperatures
About 250&#;
About 260&#;
Though lead-free HASL is common, it can't be applied to rigid PCBs with a thickness smaller than 0.5mm and flexible PCBs, neither HASL. These boards can't bear the spraying force. If you spray tin on these boards, they bend, and only the middle of the boards is sprayed with tin. Sometimes, rigid PCBs with a thickness smaller than 0.5mm may even break if you apply HASL or lead-free HASL to them.
In such cases, you can choose the other PCB surface finish -- ENIG. Or you can also change lead-free HASL to OSP. But OSP is easy to oxide. If you don't solder the PCBs at once, OSP oxides. And the manufacturer has to seal and package the OSP PCBs at once.
ENIG, also known as immersion gold, or chemical Ni/Au, is one of the best PCB surface finishes for almost all PCBs. In any case, if HASL or lead-free HASL can be used, you can replace it with ENIG. But inversely, HASL or lead-free HASL can't replace ENIG.
ENIG means plating a nickel alloy coating on the PCB pads and then a gold coating with chemical reactions. Besides PCB pads, ENIG can also be applied to other areas, such as the PCB edges or wires for thermal dissipation purposes. The thickness of ENIG is 1μm, 2μm, and 3μm. (From the equation 1mil=25.4μm, you can understand how thin the PCB finish ENIG is compared to HASL.)
ENIG PCB pads have a gold color and look shiny. Besides, the solderability of ENIG is the best among all the PCB surface finishes. And because gold has a dense crystal structure and is hard oxide, the protection of ENIG to copper of the PCB pads is also excellent.
ENIG PCBs are high-standard PCBs and they are usually used for high-end applications. As we mentioned above, ENIG can take the place of HASL and lead-free HASL in any case if your budget allows, but HASL and lead-free HASL can't replace ENIG.
Below is a comparison between EENIG and HASL.
ENIG
HASL
Lead-free HASL
Meeting lead-free requirements or not
Yes
No
Yes
Price
High
Low
Middle
Thickness
1μm, 2μm, and 3μm
25.4μm to 50.8μm
2.54μm to 25.4μm
Finish method
Chemical reactions
Spraying
Spraying
Properties
Nickel and gold
Tin and lead
Tin
Applications
Can be used for almost all PCBs
Simple FR4 PCBs with a thickness larger than 0.5mm
Common rigid PCBs with a thickness larger than 0.5mm
PCBONLINE is a one-stop advanced PCB manufacturer founded in , with two large advanced PCB manufacturing bases and one assembly factory. If you have needs for PCB and PCBA fabrication, PCBONLINE can be your reliable PCB/PCBA supplier from prototypes to bulk production.
In PCB surface finishes, PCBONLINE has these advantages:
If you need PCB design, fabrication, assembly, and box build assembly, please feel free to contact PCBONLINE by at .
This article gives an introduction to HASL and ENIG separately and compares them. ENIG is universal for PCBs, especially for high-reliability PCBs. HASL doesn't meet the lead-free requirements but lead-free HASL does. If you don't know whether HASL can be used for your PCB or not, ENIG must be okay. You can also contact PCBONLINE for suggestions.
© This article is an original work of the PCBONLINE team. Please indicate the author PCBONLINE if you reprint. If the article is reproduced without permission or indicating the author's source, PCBONLINE reserves the right to investigate the infringement.
If you want to learn more, please visit our website pcb surface finish comparison.