PCB Material:
The abbreviation "FR4" means: F (for flame) and R (forretardancies) and the 4 is a # 4 epoxy.
FR4 features high flexural, impact, superior mechanical strength and bond strength at temperatures up to 130ºC. It is possible to use standard FR-4 with minimum Tg 135ºC for double sided boards which might pass trough 2-3 soldering processes.
Surface finish:
All Printed Circuit Boards(PCB's) have copper finishes on their surface. If they are left unprotected then the copper will oxidise
and deteriorate, there are various protective finishes available,namely:
- Hot air solder levelling (HASL)
- Organic Solder Preservative (OSP)
- Electroless-Nickel Immersion Gold (ENIG)
- Immersion Silver ImAg and Immersion Tin ImSn
Hot air solder levelling (HASL), Lowest cost PCB's, remains solderable through whole manufacturing process, no negative effect at ICT
Electroless-Nickel Immersion Gold (ENIG), Excellent solderability,coplanar - flat surface, excellent shelf life, withstands multiple reflows.Higher cost (approx 5x HASL)
Soldermask
Solder mask or solder resist is a lacquer- like layer of polymer that provides a permanent protective coating for the copper traces of a printed circuit board (PCB) and prevents solder from bridging between conductors, thereby preventing short circuits. Solder mask was created primarily to facilitate wave soldering used in mass assembly. Solder mask is traditionally green but is now available in many colors
Silkscreen
Silk-screening is the process where the manufacturer prints information on the soldermask conducive to facilitate the processes of assembly, verification and repair. Generally the silkscreen is printed for indicating test points as well the position, orientation and reference of the electronic
components that are part of the circuit. Also it can be used for any purpose that the designer may require, for example, the company name, configuration instructions (this was commonly used in old PC motherboards), etc. The silkscreen can be printed on both surfaces of the board. Also the term silkscreen is known as overlay
Panelization Methods
The main considerations are V-scoring, tab routing or drill and tab routing, you can separate panel with light to moderate pressure after assembly, each method has its advantages and disadvantages:
V-scoring:
One of the main benefits from V-Scoring is that has a better panel utilization compared to the tab routing, as V-scoring don't
need spacing between small units while tab routing requires a certain width of the routing bit.
Routing:
It applied to all kinds of board shape, while V-scoring only works with rectangular shape boards, also the routed board edge is
very smooth except for the connection area, while V-cut will cause the board edge with burr after you breaking the units
away. Include the panel round rail, the idea panel dimension is about 200*300mm(7.9" by 11.8").
Board Thickness
The standard thickness of a PCB is normally around 1.6mm; for a board of this thickness it is not unusual to have a thickness
tolerance of ± 0.15mm. Note when calculating thickness that the supplier of the materials (for inner layer cores) quotes
thickness values that do not include the copper weights. So for a 0.7mm core with double sided 1oz (35μm) copper the actual
thickness will be 0.7mm + 0.035mm + 0.035mm — giving a total thickness of 0.77mm.
