A printed circuit board (PCB) mechanically supports and electrically connects electronic components using conductive tracks, pads and other features etched from copper sheets laminated onto a non-conductive substrate. PCB's can be single sided (one copper layer), double sided (two copper layers) or multi-layer. Conductor on different layers are connected with plated-through holes called vias. Advanced PCB's may contain components - capacitors, resistors or active devices - embedded in the substrate.
Surface Finish Selection
• All about the connectivity between the PCB and component devices.
• Primary function is to either temporarily protect the copper area from oxidation prior to assembly or to form the foundation of the connection to the electronic device.
• Should enhance the assembly process and promote a reliable solder joint for long-term performance.
Available Finishes
Sn/Pb Hot Air Solder Level (HASL)
Lead-Free HASL
Organic Solderability Preservative (OSP)
Immersion Silver
Immersion (White) Tin
Electrolytic Nickel/Gold (Hard & Soft Au Wire Bondable)
Electroless Nickel Immersion Gold (ENIG)
Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)
Micro Units of Measurement
• Micro-inch (1 1”) = .000001” (one millionth of a inch)
• Micro-meter (Micron) (11m) = one millionth of a meter
• One Micron (11m) = .00003937” (39 1in)
• 25.4 microns = .001” (1 mil)
Sn/Pb Hot Air Solder Level (HASL)
• Most common PCB finish in North America.
• 63% Tin / 37% Lead (“Eutectic” composition)
• Molten solder applied to exposed pads in horizontal or vertical panel orientation.
• Excess solder is blown off the circuitry with forced hot air “knife”.
• Typical thickness range of .00003” - .0015” (30-1500 1”).
• Melts at 183 degrees C.
• 12+ month shelf life (considered excellent).
Issues:
• Surface Planarity for HDI applications (highly variable topography)
• Impact of thermal excursion (extreme process temperatures)
• RoHS/WEEE restrictions and environmental issues with the use of lead.
Lead-Free Solder
Same application process (HASL) as Sn/Pb Solder.
• Common alloys: Sn/Ag/Cu (SAC), Sn/Cu/Co, Sn/Cu/Ni/Ge.
• Slightly more planar (uniform) coating than can be achieved with tin/lead solders.
• Typical thickness range of .0003”-.001” (300-1000 1”).
• Melts at 228 degrees C.
• Environmentally Friendly (RoHS & WEEE compliant).
• 12 month shelf life.
Issues:
• Low demand as PCB finish (outsourced when required).
• Aggressive on copper, depending on the alloy.
• Relatively new compared to Sn/Pb solder (less history).
Organic Solderability Preservative (OSP)
• Preserves copper surface from oxidation until assembly.
• Very thin coating (100-4000 Angstroms).
• Applied in a vertical (dip tank) or conveyorized chemical process.
• Flat, planar surface, well suited to tight-pitch pads (BGA, QFP).
• < 6 month shelf life (considered poor).
• Very manufacturable (no concerns).
Issues:
• Difficult to inspect (transparent and colorless).
• Sensitive to handling.
√typically applied as final mfg process.
• Limited shelf life.
• Requires relatively aggressive flux at assembly.
Immersion Silver
• Metallic solderability preservative.
• 8-15 micro-inches of nearly pure silver.
• Excellent solderability.
• Flat, planar surface.
• Aluminum wire bondable.
• 6-12 month shelf life.
Issues:
• Sensitive to handling, electrical test, and packaging.
Immersion Tin
• Forms a copper/tin intermetallic joint.
• Provides a dense, uniform coating with superior hole wall lubricity.
• Top choice for backplane panels assembled by pressfit pin insertion.
• Engineered to be very fine grain and non-porous.
• 6 month shelf life.
Issues:
• Sensitive to handling.
• Environmental issues with Thiourea (carcinogen) used in processing.
Electrolytic Ni/Au (Hard/Soft Bondable)
• Au electroplated in varying thicknesses over a base of electroplated Ni.
• Au hardness controlled for application (50-90 knoop = soft / 130-200 knoop = hard).
• Hard Au = 99.6% purity (Type 2, Grade C)
• Soft Au = 99.9% purity (Type 3, Grade A)
• 12+ month shelf life.
Type Thickness Comments
Gold Flash 5 – 15 inches Solderable
Full Body Gold 30 – 60 inches Trace undercut/skin effect issues
Selective Gold 30 – 50 inches Contact switches and gold “fingers”
Bondable Gold 30 – 80 inches Wire Bonding (soft Au)
Electrolytic Ni/Au Issues/Concerns
Electroless Nickel Immersion Gold(ENIG)
• Two-layer metallic coating over catalyzed copper (ion exchange).
• Ni is a diffusion barrier to the Cu and is the surface to which the soldering occurs.
• Au protects the nickel from oxidation during storage.
• Au also provides low contact resistance, excellent shelf-life, and good wetting.
• Flat, planar surface excellent for fine-pitch pads (BGA, QFP).
• 2-8 1” Au over 120-240 1” Ni.
• Good Contact Resistance (1 million + cycles).
• 12 month shelf life.
Issues:
• Electroless nickel/phosphorous can have undesirable magnetic properties.
• Aluminum wire bondable, but not gold wire.
Electroless Ni / Electroless Pd / Immersion Au(ENEPIG)
• Electroless Ni layer of 120 – 240 1” deposited on the copper surface.
• Coated with an electroless palladium layer (4 to 20 1”)
• Topped with immersion gold (2 to 8 1”).
• Forms a superior solder joint with SAC solders.
• Palladium layer eliminates corrosion potential from immersion reaction.
• Creates an ideal gold wire bondable surface.
• Allows thinner gold than electrolytic soft bondable gold, therefore less expensive.
• Fastest growing surface finish.
• 12 month shelf life.
Issues:
• Palladium does not form a strong intermetallic bond with lead in Sn/Pb solders.
Surface Finish Characteristics/Cost
Worldwide Usage by Surface Finish
About PCBWAY
PCBWay, PCB prototype and Fabrication the Easy Way!
With more than a decade in the field of PCB prototype and fabrication, we are committed to meeting the needs of our customers from different industries in terms of quality, delivery, cost-effectiveness and any other demanding requests. As one of the most experienced PCB manufacturers in China, we pride ourselves to be your best business partners as well as good friends in the every aspect of your PCB needs.
Quality
PCB is one of the most crucial parts of any electrical and electronic devices. The quality of PCB determines the quality of all these devices. The modern technology makes possible the increasing miniaturization of integrated circuits, higher packing density and smaller layout dimension, hence the higher demands on PCB arise. We fully understand the importance of PCB quality for our customers and therefore we visually check every board, and we electrically test them again to ensure our shipped boards exactly comply with your Gerber files.
Delivery
Through the years we are proud to have been keeping an on-time delivery rate of 99%. We know, apart from PCB quality, the other most important factor is the shortest possible lead-time, which is crucial for engineers’ R&D works, especially in the stage of prototyping. We work in three shifts to make sure your PCBs will be on your desk as agreed up and as early as possible.
Pricing
Our pricing structure is transparent and has no hidden cost in it. Our price is one of the most competitive in the world, and is just a fraction of what other American or European fabricators normally charge you. Even many price-sensitive customers like students and hobbyists largely rely on us for their PCB prototype and fabrication orders. We try our utmost to save your money and time.
PCBWay’s vision--to be the best PCB prototype and low-volume production manufacturer in the world!
