The three layer PCB board above products called PCB board, double panel for parts with traditional intensive assembly, can not accommodate so many components and derived from a large number of line in the limited surface, thus the development of multilayer PCB board.
With the Federal Communications Commission (FCC) announced that since October 1984, all listed electrical products if there is involved in telecommunications, or participate in online, all must be "grounded" in order to eliminate the interference. However, due to the surface area is not enough, so pcblay-out will be "ground" and "voltage" two function of the large copper surface into the inner layer, resulting in a large number of the rise of the four layers of PCB board, but also extends the requirements of impedance control.
The original four PCB board is upgraded to six PCB board, of course, the high level PCB board but also because of the high density assembly and increasing. This chapter will explore the inner PCB board production and pay attention to matters.
Production process
According to the different products of the existing three processes
A.Print and Etch
Outgoing, alignment hole, copper surface treatment, image transfer, etching, stripping
B.Post-etch Punch
Materials, copper surface treatment, image transfer, etching, stripping film, tool hole
C.Drilland Panel-plate
Materials, hole drilling, hole, electroplating, image transfer, etching, stripping
Issue
Work is in accordance with the system design planning work according to the cutting size, BOM substrate, is a very simple procedure, but must pay attention to the following points:
A. cutting method - will affect the size of the blanking
B. edge and fillet considerations - Impact Image yield process
The direction of C. must be consistent, i.e., the direction of the opposite direction, the direction of the weft
D. made before baking - size stability considerations
Copper surface treatment
In the process of printed circuit board, regardless of the step, copper surface cleaning and coarsening of the effect, the relationship between the success or failure of the next process, so it seems simple, in fact, there is considerable knowledge.
A. copper surface treatment process has the following
A. dry film lamination
B. oxidation pretreatment
C. after drilling
D. chemical copper
E. before copper plating
F. green paint
G. spray tin (or other pad handling process)
H. gold finger before nickel plating
In this section, we discuss the best way to deal with a.c.f.g. and other processes (the rest are part of the process automation, and do not have to be independent)
B. processing method
The current copper surface treatment can be divided into three kinds:
A. brush grinding (Brush)
B. sand blasting (Pumice)
C. chemical method (Microetch)
The following is the introduction of these three methods
Brush grinding
The effective length of the A. brush wheel needs to be uniformly used, otherwise the surface of the brush wheel is not uniform
B. to do the brush test to determine the depth and uniformity of the advantages of brush
A. low cost
B. process is simple, elastic defects
A. thin circuit board is not easy to carry out
B. substrate elongated, not suitable for the inner lamella
C. brush marks are easy to cause the D/F adhesion is not easy and infiltration plating
The potential for D. to have residual gum
Sand blasting
With different materials of fine stone (commonly known as pumice) as the advantages of abrasive materials:
The surface roughness uniformity of A. is better than that of brush grinding
B. dimensional stability is better
C. can be used for thin plate and thin wire:
A.Pumice easy to stay on the floor
B. machine maintenance is not easy
Chemical method (micro etching)
Image transfer
Printing method
Circuit board from its origin to the current high density design, Printing screen printing (SilkScreen) - or screen printing has a close relationship, it is called "printed circuit board". At present, in addition to the most widely used in circuit board, there are other electronics industry (Thick Film) thick film hybrid circuit (Hybrid, CIRcuit) (Chip Resist), chip resistance and surface mount (Surface Mounting) of the solder paste printing also has excellent application.
In recent years, the circuit board of high density, high precision printing method has been unable to meet the specification requirements, so the application range gradually reduced, while the dry film method has replaced most of image production methods. The following is to process printing method cover:
A. single panel circuit, solder resist (lot production using automatic printing, the following same)
B. single panel carbon ink or silver glue
C. double-sided board circuit, welding
D. wet film printing
E. inner copper surface
F. text
G. (Peelableink) adhesive
In addition, the printing technician training difficulties, high wages, while the cost of dry film method is gradually reduced so that both the growth and decline significantly
Brief introduction of A. screen printing (Screen Printing)
Several important basic elements: screen printing mesh material, screen, emulsion, exposure machine, printing machine, scraper, ink, oven, following one by one simple introduction.
A. mesh material
(1) according to the different materials can be divided into silk (silk), Niron (nylon), polyester (Polyester, or tetolon), stainless steel, etc. the circuit board used for three.
(2): the most commonly used method of weaving also is best to use Plain Weave monofilament flat weave.
(3) the number of mesh (mesh), fabric thickness (thickness), diameter (diameter), the opening (opening) relationship
Opening:
Net mesh size: each inch or cm in the opening number
Wire diameter: mesh diameter of mesh cloth
Thickness: thickness specifications are six, Slight (S), Medium (M), Thick (T), Half heavyduty (H), Heavyduty (HD), Super (heavyduty) (SHD)
B. screen (Stencil) type
(1). Direct screen (Direct Stencil)
The emulsion evenly coated directly on the mesh, even after the drying box placed in the common exposure equipment table and covered with the original film, then the vacuum contact sensitization is formed by imaging screen printing. Usually latex many times, as the printing thickness. This screen is durable, high stability, for mass production. But the production is slow, probably due to the uneven thickness and resolution is poor and too thick.
(2) indirect screen (Indirect Stencil)
The photographic film is transferred from the original film to the original film in the form of exposure and imaging, and then the printed film of the existing pattern is pasted on the surface of the net