- Dec 13, 2017 -
PCB circuit board inner-layer production and inspection skills
Three-layer PCB board and above product is called multi-layer PCB board,the traditional double-sided board for the dense assembly of parts, unable to place so many components and the large number of lines generated on the limited board, therefore, there is multilayer PCB board development.In addition, the Federal Communications Commission (FCC) announced that after October 1984, all the listed electrical products, if there are telex communicators or people involved in the online connection, must have "grounding" to eliminate the impact of interference.However, due to the lack of surface area, pcb lay-out will "ground" and "voltage" two functions of the copper surface into the inner layer, resulting in a large number of PCB four layers of the instant rise. It also extends the requirement of impedance control.
The original four layers PCB board is upgraded to six layers PCB board, of course, the high level multilayer PCB board assembly and also because of the high density increasing.
This chapter will discuss the production and attention of the inner layer of multi-layer PCB board
There are three existing processes according to the different products
A. Print and Etch
Issuance of materials→ registration hole→ copper surface treatment→ image transfer→ etching→ stripping of film
B. Post-etch Punch
Issuance of materials→ copper surface treatment→ image transfer→ etching→ stripping of film→tooling hole
C. Drill and Panel-plate
Issuance of materials→Drilling hole→through-hole→ electroplate→ image transfer→ etching→ stripping of film
Issuance of materials
Issuance of materials is in accordance with the planning design work size,, according to BOM to cut the substrate, is a very simple step, but the following points to note:
A.Cutting method will affect the size of the material
B.Consideration of the edge and corner of grinding - influence on the rate of image transfer
C.Baking before under the process - size stability considerations
Copper surface treatment
In the process of printed circuit board, no matter which step, the effect of cleaning and coarsening of copper surface is related to the success or failure of the next process, so it seems simple, but in fact, its knowledge is quite large.
A. the following processes require copper surface treatment
a. Dry film lamination
b. Before inter-layer oxidation treatment
c. After drilling hole
d. Before Chemical copper
e. Before copper plating
f. Before paint green lacquer
g. Before spray tin (or other welding pad treatment process)
h. Before gold fingers plating nickel
This section explores the best way to process a. c. f .g. Processes (the rest is part of process automation and does not need to be independent)
B. processing method
The current treatment of copper surface can be divided into three kinds:
a. brush grinding (Brush)
b. sand blasting method (Pumice)
c. chemical method (Microetch)
Brush grinding method
a.The effective length of the brush wheel should be used evenly, otherwise the surface of the brush wheel will be uneven.
b. is required to do brush mark experiments to determine the advantages of brush depth and uniformity
d. process is simple
a.thin circuit board is not easy to carry out Elongated
b.Substrate elongated, unsuitable inner-layer thin board
c.When the brushmark is deep, it is easy to cause D/F adhesion and plating
d.The potential of residual glue
Sand blasting method
The fine stones of different materials (commonly known as pumice) are the advantages of grinding materials:
a.The roughness and uniformity of surface is better than that of brush grinding
b. has good stability in size
c. can be used for defects of thin board and fine lines
a. Pumice is easy to stick to the board surface
b. machine is not easy to maintain
Circuit board design from its origin to the present high density design has always been directly related to silk Screen printing-or screen printing. Therefore, it is called "printed circuit board". At present, in addition to the maximum number of applications in the circuit board. In other electronics industries, there is a hybrid hybrid circuit with thick film Thick Film.The chip resistor is chip Resist. And surface mount surface tin paste printing and so on are also excellent applications.
Due to the high density and high precision requirements of printed circuit boards in recent years, printing methods have been unable to meet the specifications, so its application scope has been shrinking. Dry film method has replaced most of the image transfer production methods. The following is the process of printing cover.
a. Circuit of single side board, welding resistant (mass production more use of automatic printing, below is the same )
b. single board of carbon or silver
c. Circuit of double side board, welding resistant
d. Wet film printing
e. Inner layer of large copper surface
g. Peelable ink
In addition, printing technicians are difficult to train and pay high. The cost of dry film process is decreasing gradually.
A. brief introduction to the screen printing
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 printing screen. Usually latex many times, as the printing thickness. This screen is durable and stable high, for mass production. But the production is slow, probably due to the uneven thickness and resolution is poor and too thick.
(2) .Indirect Stencil
The photographic film version to exposure and imaging from the original negative on the graphics transferred, then the film version of graphic stickers on the screen surface, the cold air drying after tear off the transparent carrier film is indirect screen. Its uniform thickness, good resolution, faster production, for samples and small mass production.