PCB Surface Salvage Solutions Pros & Cons
PCB Surface cease gain the serious interface between the board and the parts. In fresh years, their frequent availability has overwhelmed some electronic designers. This post hopes to shed some gentle on the execs and cons of the four most dominant PCB surface cease suggestions on the market: Natural Solderability Preservative (OSP), Electrolysis Nickel Immersion Gold (ENIG), Electroplated Nickel Gold and Immersion Tin or Silver. The next post applies to Rigid Printed Circuits Boards (PCB) and Flexible Printed Circuit (FPC).
Repeat: PCBs are normally made of rigid materials and will no longer bend accurate by their application. FPCs are normally thin and made of materials suitable of bending and / or hotfoot accurate by application. Processing and application requirements dictate whether the PCB surface cease is electroplated, electrolysis, immersion or deposited.
- Prerequisites that affect PCB Surface Salvage Preference:
- Oxidation protection of PCBs steel traces (normally copper).
- Surface solderability for electrical and mechanical issue attachment.
- Surface bondability for chip mounted parts the utilization of gold and aluminum wire.
- Any combinations of the above.
- Mechanical purposes (eg stress, lines etc.).
- Environmental prerequisites (eg temperature, relative humidity etc.).
- Mechanical contacts requiring abrasion resistance and oxidation protection.
- General Dialogue of Accessible Surface finishes
Natural Solderability Preservative (OSP)
OSP has a restricted shelf lifestyles. Its most frequent use is soldering when the protectant is dissipated accurate by the job, thus no additional elimination processes are wished.
Warning: as soon as eliminated, the bare copper is uncovered and arena to oxidation. When lots of finishes are wished on the identical PCB, OSP will also be utilized over differing kinds of surface cease (eg wire bonding and soldering, mechanical contact surfaces and soldering, etc.).
Electrolysis Nickel Immersion Gold (ENIG)
ENIG is a broadly aged surface cease for soldering, aluminum wire wedge bonding and mechanical contact components (connector pads, test components, etc.). The copper surface has an electrolysis nickel layer deposited (150 micro inches minimum) to seal the copper. A layer of gold is then deposited to guard the nickel from oxidation and present a solderable surface to the nickel. The gold is absorbed and dispersed into the solder. The gold is an immersion job and the thickness is self-limiting (2 to some micro inches max).
The nickel layer is extraordinarily brittle and can not be subjected to emphasize or lines in the Z axis without cracking. Flexible PCBs are especially liable to this with all areas arena to capability bending supported with rigidizing materials.
Warning: Improperly controlled ENIG processing could perhaps perhaps no longer sleep in frail solder connections that could perhaps perhaps well no longer be visible and / or result in failure. A normal signal of failure is a flat sunless copper pad after the linked issue has been forcibly eliminated.
Electroplated Nickel Gold
In on the unique time's complex circuits, this surface cease is extraordinarily restricted on anecdote of it requires that every surfaces to be plated have to be electrically linked (ie an electrical charge have to be show for plating). These interconnections must then be broken to gain the circuit purposeful. The plated nickel is extraordinarily solderable and never arena to the solderability complications with ENIG. The plated gold has no limits on thickness and can enhance wire-bonding processes devour Thermo Compression Bonding (ie ball bonding).
Warning: Thicker gold could perhaps perhaps no longer sleep in solder joints being too brittle when the utilization of lead primarily based entirely solders.
Immersion Tin and Immersion Silver
These processes present solderable surfaces but are inclined to have oxidation and tarnish components that affect solderability. They’re no longer broadly aged or accessible.
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