PCB (Printed Circuit Board)
1.) Classify by Rigid or Flex
1.1) Rigid PCB
Most PCB is rigid PCB that use with the general application from normal / base electronic equipment/device until aerospace, avionics, military, medical device
1.2) FPC (Flexible Printed Circuit Board)
FPC is use for the application device which need to be bend or curve area and also a small area such as Printer pare wires , digital camera, game, hard disk drive, mobile phone, car gauge meter console.
1.3) Rigid + Flex PCB
Use bothe Rigid and Flex PCB in the same PCB which depend on user design.
2.) Classify by Complexity of PCB layer
2.1) Single Side PCB
Single-Side PCB is the simplest and most common type of PCB. It was the first device used for the interconnection and assembly of electronic components forming a cohesive and functional operating system. The primary industry that uses these boards is the consumer electronics industry.
2.2) Double Side PCB
Double Side PCB have made circuit in 2 layer of different PCB side that both layer has connect by via PTH (Plated Through Hole) which depend on design this is more complex than Single Side PCB.
2.3) Multi Layer PCB
Multi Layer PCB have more layer than double side PCB, it has many circuit layer between Top side and Bottom side of PCB and also each layer can connect with via PTH (Plated Through Hole), this type is more complex than double side PCB.
2.4) High Density Interconnect (HDI) PCBs
HDIs have a higher circuit density per unit area than the conventional multi-layered PCBs. They also have a smaller hole diameter, a higher line density and a greater connecting density with more connecting points per square inch than that employed in conventional PCB technology. HDIs are used to reduce size and weight, as well as to enhance the electrical performance of electronic products such as those found in smartphones nowadays.
3.) Classify by Surface Finish
3.1) Hot air solder levelling (HASL)
HASL is the cheapest surface finished which is the method of diping the PCB into the molten solder bath so he copper surfaces are covered by solder.
Brief Process Flow of HASL
Step 1 : Pre-Clean ==> Done with micro-etch
Step 2 : Fluxing ==> To protect oxidation, Affect heat transfer during solder immersion.
Step 3 : Hot Air Leveling ==> For SnPb Molten solder temperature 460 F (237 C), For Lead-Free not yet have information.
Step 4 : Post-Clean
Typical Thickness : 25 - 2,000 Micro inches (mils)
Advantages of HASL
- Excellent wetting during component soldering
- Easily applied
- Easily Rework component
- Good bond / joint strength after PCBA
- Long Shelf Life
- Easy to visual inspection
Disadvantages of HASL
- Low planarity makes this surface finish unsuitable for use with fine pitch components, high risk to have solder paste printing and assembly defect.
- High thermal stress during process may introduce defects to PCB.
- High risk to generate solder bridging on fine pitch component.
- Inconsistence coating thickness (on vary pad size).
3.2) Organic Solder Preservative (OSP)
OSP is the coating the thin organic on copper surface that was simple and easy way to do and the thin OSP coated will limited the number of passing heat cycle 2 - 3 times maximum because the organics coated will be disappear about 25 % every times pass heating (especially reflow process)
Typical Thickness : 8 - 24 Micro inches (mils), 0.2 - 0.6 microns
Advantages of OSP
- Flat, Coplanar pad
- Reworkable
- Low cost
- Short and easy process
- Good solder mask intergrity
Disadvantages of OSP
- The thin coating is effect to reliability when pass many time of heat
- Sensitive to some solvent, if need clean after mis-print need to check solvent, some solvent may effect the coating removed that leading to exposed copper problem.
- Limited shelf Life
3.3) Electroless-Nickel Immersion Gold (ENIG)
Plate Nickel on copper then plate Gold on Nickel
Typical Thickness :
==> Nickel 125 - 250 Micro inches (mils)
==> Gold 3 - 8 Micro inches (mils)
Advantages of ENIG
- Long Shelf Life
- Excellent flat planarity, consistence thickness
- Withstands multiple reflows
- Good Solderability
- Good for fine pitch component.
Disdvantages of ENIG
- The electroless nickel layer is brittle and has been found to break up during mechanical stress. This effect is known in the industry as 'black pad' or 'mudflat cracking'. This has lead to bad press for ENIG
- Higher cost (5X HASL)
- Not wire-bondable
- Too high Gold thickness generate de-wetting problem when soldering because too high thickness of gold is hard to absorb heat.
- Can not rework surface finished (ENIG) at PCB fabricator.
3.4) Immersion Silver (Ag)
Typical Thickness :
==> 5 - 25 Micro inches (mils)
Advantages of Immersion Silver
- Good for fine pitch component
- Planar Surface
- Inexpensive
- Short, easy process cycle
- Long shelf life
- Can be reworked the silver surface at PCB fabricator
- Compatible for Lead-Free process.
- Surface suitable for electrical contact
- Capable of multiple reflow cycles
Disdvantages of Immersion Silver
- Tarnish must be controlled
- Rapid degradation of surface due to oxidation or contamination (with e.g. sulfur or chlorine)
- Not good for sliding connectors
- Occasional voiding
- Deposit gradually discolors due to air exposure
3.5) Immersion Tin (Sn)
Typical Thickness :
==> 25 - 60 Micro inches (mils)
Advantages of Immersion Tin (Sn)
- Good for fine pitch component
- Planar Surface
- Inexpensive
- Good solderability / hole filling ? ?
- Suitable for press-fit applications because no burr appears
Disdvantages of Immersion Tin (Sn)
- Limited rework cycles
- Sensitive on scratches
- Sensitive on thermal influence and improper storage conditions
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Reference
http://www.kingboard.com/Item/list.asp?id=1234http://easypcb.xonelectronics.com/surface_finish_options.htm
http://en.wikipedia.org/wiki/HASL
http://www.saturnelectronics.com/technology_hub/immersion_silver_finish.html
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