7. The design of PCB(multiple layer board)-- Process of multilayer board

Multiple Layer Board
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PCB Multilayer Board means multilayer board used in electrical product, it involves wild area, such as home appliance, computer accessories, communication, toy, instrument, LED and so on.
PCB(printed circuit board) Multilayer Board is consist of track on several layer of insulation substrate and pad, it has two function: conduct every layers circuit, insult mutual layer. As the develop of SMT, the launch of new SMD (such as QFP, QFN, CSP, BGA), electrical product become more intelligent and smaller. Since HDI is created, the develop these process technology lead the design of PCB to multiple layer, and high density.  

1. Process of multilayer board
  1. PCB which has draw the track:
Put on the board, acidity deoiling, scanning rinsing, second reflux rinsing, micro etch, scanning rinsing, second reflux rinsing, presoak copper plating, copper plating, scanning rinsing, presoak tin plating,  tin plating, second reflux rinsing, off the board.
2. Detail of multilayer PCBs process
2.1 presoak of tin plating
2.1.1  consist of tin plating and operating conditions of tin presoak
2.1.2  method of tin plating   
  Add half vat of distilled water, then add 15L vitriol whose mass fraction is 98%, add 1.5 L sulfotech part A after the water and vitriol has being stir in to cool, stir them, then add distilled water to make all of them reach 300L, stir well, then it can be use.
2.1.3  Maintenance and controlling of presoak tin plating
  Deal 100 board need 1L vitriol and 100mL Sulfotech Part A, the bath will be replaced after dealing 1500board.
2.2  Tin Plating
2.2.1  Combination and operating conditions of tin plating electrolyte 
2.2.2  Method of open tin pot
Add half vat of distilled water, add vitriol whose mass fraction is 98%, after them cool down, add 40 kg Tin Salt 235, cool them to 25 ℃, then add 76L Sulfotech Part A, 15.2 L Solfotech Part B, 30.4L STH Additive Sulfolyt, finally, add distilled water to liquid level.
2.2.3  Maintenance and controlling of presoak tin plating
Deal per 100 board, need 11L vitriol, 600g Tin Salt 235, 600mL Sulfotech Part A, 800mL Sulfotech Part B, 750mL STH Additive Sulfolyt. Auto add system add 56mL Sulfotech Part A per 200AH.
Solution must be test by Hull cell test, observe and adjust Sulfotech Part A, Sulfotech Part B.
Item               Range          the Best Value
Sn2+               20-30mL/L      24mL/L
W(H2SO4)(98%)       160-185mL/L    175mL/L
Sulfortech Part A      30-60mL/L      40mL/L
STH Additive Sulfolyt   30-80mL/L      40mL/L
Sulfotech Part B       15-25mL/L       20mL/L
Operate temperature   18-25         22
Cathode-current density  1.3-2 ASD      1.7ASD



11. The design of PCB (multiple layer board)--Basic requirement of designing multiple layer PCB VOL3