| Surface finishes for PCBs fluctuate in reliability, shelf | | | | In the past users recognized ENIG as the best flat (fine |
| life, flatness, price, and assembly procedures. All | | | | pitch) surface and lead-free choice in the world. This |
| finishes have their own benefits; however, the process, | | | | surface finish holds several advantages, including |
| product, and / or final use determine which surface | | | | exceptional shelf life and long-term experience and/or |
| finish works best for use with a specific application. | | | | knowledge of the product. Nickel thickness generally |
| The designer, end-user or assembler needs to work | | | | measures 75 micro inches, compared to three to five |
| with the PCB manufacturer to choose the correct | | | | micros for gold. The surface finish also possesses |
| finish for the product design. | | | | some disadvantages, including a higher cost, two-part. |
| Hot Air Solder Leveling (HASL) | | | | In addition, in situations of an uncontrolled process you |
| Hot Air Solder Leveling, a 63/37 tin lead solder, has | | | | may see the quality issue known as "Black Pad." Here |
| served as the industry standard since the start of the | | | | at Sierra Circuits, after years of working with ENIG, we |
| circuit board.. HASL is the favorite because "Nothing | | | | have eradicated the "Black Pad" problem. By carefully |
| Solders like Solder." In situations where you have no | | | | varying gold thickness, we have been able to figure |
| concern about lead, HASL proves cost effective as | | | | out the ideal thickness for the gold to make sure that |
| well as a reliable finish for the making of PCBs of | | | | our customers never see Black Pads. |
| standard technology. This finish does, however, further | | | | Immersion Tin |
| stress on high layer circuit boards, resulting in | | | | Tin immersion process, more popular in the past, offers |
| ineffective long-term use. The added stress, short | | | | a consistent flat surface about 20-40 micro inches |
| shelf life, and uneven soldering height on thick SMT or | | | | thick. It solders well and remains cost efficient. |
| BGA pads make HASL a bad choice for wire bonding | | | | However, the finished PCBs have a limited shelf life |
| or chip technology. New technologies, tighter design | | | | necessitating you use them within three to six months. |
| principles and environmental issues are starting to | | | | PCB factories worldwide have this process in place. It |
| make HASL obsolete. There are many Lead-free | | | | is also perfect for Lead Free assembly. |
| alloys that can replace the 63/37 tin lead solder | | | | Organic Solderability Preservatives (OSP) |
| process to make the board ROHS or Lead Free. | | | | Organic Solderability Preservatives began in the 1970s |
| Lead-Free Hot Air Solver Level (LF HASL) is the | | | | and provide a thickness so fine you almost can't |
| ROHS compliant version of HASL. It is applied in the | | | | measure it. The first formulas offered a limited shelf life |
| same but it is a different composition of the Solder. To | | | | of three to six months and withstood only one or two |
| comply with Lead-Free, the lead is removed and | | | | heat cycles, but today the newest OSP formulas offer |
| replaced by Gold, Nickel or other metals depending on | | | | much more because of their construction for lead free |
| your PCB manufacturer - thus the thickness varies | | | | assembly and provide shelf life 12 months as well as |
| anywhere between 1 to 15 mm. | | | | the ability to handle numerous heat cycles. |
| Immersion Silver | | | | Electroless Nickel - Electroless Palladium - Immersion |
| Immersion Silver is a very simple process. The silver | | | | Gold (ENEPIG) |
| replaces the copper during the immersion process. It is | | | | ENEPIG Is considered by many people call it - the |
| quickly gaining recognition as a lead-free surface finish | | | | "Universal" finish. Is a combination of three metals- |
| because of its lower cost (Compared to ENIG), | | | | nickel, palladium and gold. It is considered the best |
| uniform thickness and the capability to withstand the | | | | surface finish for Lead-Free assembly and wire |
| lead-free assembly temperatures. Immersion silver has | | | | bonding. Because of the combination of the three |
| a shelf life of one year. Over the past year PBC | | | | metals, it has the best galvanic resistance. The |
| facilities installed silver process lines more than any | | | | palladium separates the gold from the Nickel to |
| other type of finish. Immersion silver has a controlled | | | | prevent noise voltage and stop corrosion. Also, |
| thickness of five to twelve micro inches and remains | | | | because of the falling price of Palladium, it has become |
| cost efficient, compatible with the majority of assembly | | | | very reasonably priced. Sierra Circuits is one of the |
| processes. | | | | leading PCB manufacturers to offer ENEPIG. |
| Electroless Nickel/Immersion Gold (ENIG) | | | | |