Immersion Tin is a RoHS compliant (lead-free) surface finish that is an ideal choice for flat surface requirements and fine pitch components. The tin layer’s appearance is usually mostly white, so the finish is sometimes referred to as White Tin. Immersion Tin is a deposit of a thin layer of Tin on Copper layer of a PCBs, that can protect the copper beneath from oxidation throughout the PCB’s intended shelf life. It is not used as often as other surface finishes because not all PCB manufacturers offer it. The flatness of this particular coating makes this an ideal surface finish choice for small geometries and components.
Immersion Tin is the least expensive of all types of coatings. It is very economical; however, it does come with certain shortcomings. One of the main drawbacks of immersion Tin is, once you deposit the tin onto copper, it will begin to tarnish. This also means if you wish to avoid low quality solder joints, it is imperative to do your soldering activity within 30 days. Below are advantages and disadvantages of immersion tin surface finish.
|Immersion Tin PCB||• It is a lead-free surface finish|
• It is highly reliable and produces fine quality
• It produces planar or flat surfaces
• One of the most cost-effective PCB surface finishes available in the market
• Top Choice for Press Fit Pin Insertion
|• Easy to Cause Handling Damage|
• Process Uses a Carcinogen (Thiourea)
• Exposed Tin on Final Assembly can Corrode
• Tin Whiskers
• Not Good for Multiple Reflow/Assembly Processes
• Difficult to Measure Thickness
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.
Immersion silver is a non-electrolytic chemical finish applied by immersing the copper PCB into a tank of silver ions. It is a good choice finish for circuit boards with EMI shieldingand is also used for dome contacts and wire bonding. The average surface thickness of the silver is 5-18 microinches.
Comparison With These Surface Finishes
·The features of immersion silver as surface finish place it in between OSP and immersion gold. Even when exposed to humidity, heat, and pollution, immersion silver continues to provide good solderability and electrical connection, although it will tarnish. Immersion gold has a layer of nickel under it, which provides it with physical strength. As there is no nickel layer under immersion silver, its physical strength is lower than that of immersion gold.
·Immersion silver requires more care for storage and handling than immersion tin does. However, immersion silver is safer for the environment than immersion tin is.
·Immersion silver is easier to use compared to Organic Solder Preservative or OSP is.
·Immersion silver offers a more planar surface than HASL does.
It is important to select the appropriate surface finish for your project by considering the various options while factoring in performance requirements and material costs.
|Surface Finish||Content||Technological Capability|
(According to IPC-4554)
|Max panel size||406*533mm|
|Board thickness||0.20 – 3.2mm|
|Immersion Tin thickness||0.75-1.2um|
Immersion tin is applied using an electroless chemical bath that will apply approximately 0.7 to 1.0 microns (or about 44 micro inches) of tin to the copper. You should also adhere to the correct requirements of temperature, time, and bath composition to make the process successful.
If you have any questions about Immersion Tin or any other pcb finish, or to send along your PCB Design Files for an official quotation, please feel free to Contact Us at any time! VictoryPCB is a professional pcb fabrication and pcb assembly manufacturer, supplying high quality printed circuit board products and services to our clients worldwide.