What is the process of PCB inner layer production?

What is the process of PCB inner layer production?

1. Process classification

According to the number of PCB layers, it is divided into single panel, double panel, and multi-layer board. The three board processes are not the same.

Single-sided and double-panel have no inner layer process, basically cutting material-drilling--subsequent process;

Multilayer board will have inner layer process

1) Single panel process

Cutting edging → drilling → outer layer pattern → (full plate gold plating) → etching → inspection → silk screen resistance welding → (hot air leveling) → silk screen characters → shape processing → test → inspection

2) Double-panel tinplate process

Cutting edging → drilling → thickening of copper ● outer layer pattern → tin plating, etching tin removal → secondary drilling → inspection → silk screen resistance welding → gold plating plug → hot air leveling → silk screen characters → shape processing → test → test

3) Double-panel nickel-plated gold process

Cutting edge grinding → drilling → thickening of copper ● outer layer pattern → nickel plating, gold film etching → secondary drilling → inspection → silk screen soldering → silk screen characters → shape processing → test → inspection

4) Multi-layer board tin plate process

Cutting edge grinding→Drilling positioning hole→Inner layer pattern→Inner layer etching→Inspection→Blackening→Lamination→Drilling→Pinking thickening→Outer pattern→ Tin plating, etching tinning→Secondary drilling→Inspection →Silk screen soldering→gold-plated plug→hot air leveling→screen printing characters→shape processing→test→test

5) Multi-layer plate nickel-plated gold process

Cutting edge grinding→Drilling positioning hole→Inner layer pattern→Inner layer etching→Inspection→Blackening→Lamination→Drilling→Pinking thickening→Outer pattern→Gold plating, film removal etching→Secondary drilling→Inspection→ Screen printing solder mask → silk screen characters → shape processing → test → inspection

6) Multi-layer plate nickel-plated gold plate process

Cutting edge grinding→Drilling positioning hole→Inner layer pattern→Inner layer etching→Inspection→Blackening→Lamination→Drilling→Pinking thickening→Outer pattern→ Tin plating, etching tinning→Secondary drilling→Inspection →Silk screen soldering→Chemical nickel-plated gold→Screen printing characters→Shaping processing→Test→Inspection

2. Inner layer production (graphic transfer)

Inner layer: panel, inner layer pretreatment, lamination, exposure, DES connection

(1) Cutting board

Cutting (Board Cut)

Purpose: Cut the large material into the size specified by the MI according to the order requirements (cut the substrate material to the required size according to the planning requirements of the pre-design)

Main raw materials: substrate, saw blade

The substrate is made of copper sheet and insulating laminate. It has different thickness specifications according to requirements. According to copper thickness, it can be divided into H/H, 1OZ/1OZ, 2OZ/2OZ, etc.

Precautions:

a. Avoid the impact of the edge of the board, the edge is trimmed, rounded

b. Considering the effect of expansion and contraction, the cutting board is baked before being sent to the process.

c. Cutting should pay attention to the principle of consistent mechanical direction

*Blank/rounded corners: remove the glass fiber left at right angles on the four sides of the board by mechanical grinding to reduce the scratch/scratch of the board during the post-production process, resulting in quality hazards

*Bake plate: removes water vapor and organic volatiles by baking, releases internal stress, promotes cross-linking reaction, increases sheet dimensional stability, chemical stability and mechanical strength

* Control point:

a Sheet: panel size, board thickness, sheet type, copper thickness

b. Operation: baking sheet time / temperature, stack height

(2) Inner layer production after cutting

Function and principle

The inner layer copper plate roughened by the grinding plate is dried by a grinding plate, and after being coated with a dry film IW, it is irradiated with UV light (ultraviolet light), and the dry film after exposure becomes hard, and cannot be dissolved in the case of weak alkali, and can be dissolved in the presence of a strong alkali. The unexposed part can be dissolved by the weak base, and the inner layer is used to transfer the pattern to the copper surface by using the characteristics of the material, that is, image transfer.

Detail : (The photoinitiator in the resist area absorbs photons into free radicals, and the radical initiates cross-linking reaction to form a spatial reticulated macromolecular structure insoluble in dilute alkali, while the unexposed part is not The reaction is soluble in the dilute alkali. The image transfer can be achieved by transferring the pattern on the film to the substrate by using different solubility properties in the same solution.

The line pattern requires higher temperature and humidity conditions, generally requiring a temperature of 22 +/- 3 ° C and a humidity of 55 +/- 10% to prevent deformation of the film. The dust level in the air is high, and the density of the line is increased and the line is smaller. The dust content is less than or equal to 10,000.

Material introduction

Dry film: dry film photo-etching agent Dry film (Dry film) is a water-soluble resist film, the thickness is generally 1.2mil, 1.5mil and 2mil, etc., divided into polyester protective film, polyethylene diaphragm and photosensitive film three layers. The function of the polyethylene separator is to prevent the soft film-blocking agent from sticking to the surface of the polyethylene protective film during the transportation and storage time. The protective film prevents oxygen from penetrating into the resist layer and reacts with free radicals to cause photopolymerization. The dry film which is not polymerized is easily washed away by sodium carbonate solution.

Wet film: wet film is a one-component liquid photosensitive film, mainly composed of high-sensitivity resin, sensitizer, colorant, filler and a small amount of solvent. The viscosity of production is 10-15dpa.s, which has corrosion resistance and electroplating resistance. , wet film coating methods are screen printing, spraying, etc.

Process introduction

Dry film imaging, the production process is as follows

Pretreatment - lamination - exposure - development - etching - removal of film

Pretreate

Objective: To remove impurities such as grease oxide layer on the copper surface and increase the roughness of the copper surface to facilitate the subsequent lamination process.

Main raw materials: brush wheel

Pre-processing method:

(1) Sandblasting method (2) Chemical treatment method (3) Mechanical grinding method

The basic principle of chemical treatment: the chemical substances such as SPS and other acidic substances evenly bite the copper surface to remove impurities such as grease and oxide on the copper surface.

Chemical cleaning: use alkali solution to remove oil stains on the copper surface, fingerprints and other organic contaminants, and then use an acidic solution to remove the protective coating on the oxide layer and the original copper substrate that does not prevent copper from being oxidized, and finally perform microetching treatment to obtain A fully roughened surface with excellent adhesion to dry film.

Control points

a. grinding speed (2.5-3.2mm/min)

b. wear scar width (500# needle brush wear scar width: 8-14mm, 800# non-woven fabric wear scar width: 8-16mm), water mill experiment, drying temperature (80-90 ° C)

lLamination

Purpose: Apply the treated copper surface to the dry film through hot pressing

The main raw materials: dry film (Dry Film), solution imaging type, semi-aqueous solution imaging type, water-soluble dry film mainly consists of organic acid salts, which will react with strong alkali to make it an organic acid radical. Dissolve

Principle: dry film (film): first peel the polyethylene protective film from the dry film, and then paste the dry film resist on the copper clad plate under heat and pressure, the resist in the dry film The layer is softened by heat, and the fluidity is increased, and the film is completed by the pressure of the hot press and the action of the binder in the resist.

Three elements of dry film: pressure, temperature, transfer speed

Control points

a. film speed (1.5 +/- 0.5m / min), film pressure (5 +/- 1kg / cm2), film temperature (110 + / - 10 ° C), plate temperature (40-60 ° C)

b. Wet film coating: ink viscosity, coating speed, coating thickness, pre-bake time / temperature (5-10 minutes on the first side, 10-20 minutes on the second side)

l Exposure

Purpose: Transfer the image on the original film to the photosensitive substrate by the action of the light source

The main raw material: the inner film used in the inner layer of the film is a negative film, that is, the white light transmitting portion is polymerized, the black portion is opaque, and the hair is not generated, and the film used for the outer layer is a positive film, and the inner film is opposite to the inner film. Exposure principle: the photoinitiator in the exposed area resist absorbs photons into free radicals, and the radical initiates cross-linking reaction to form a spatial reticulated macromolecular structure insoluble in dilute alkali.

Control points: accurate alignment, exposure energy, exposure ruler (6-8 cover film), dwell time

Developing (Developing)

Purpose: Wash out part of the dry film that has not undergone chemical reaction with lye

Main raw material: Na2CO3

The dry film which has not been polymerized is washed away, and the dry film which is polymerized remains on the surface of the plate as a resist layer for etching.

Development principle: the active group in the unexposed portion of the photosensitive film reacts with the dilute alkali solution to form a soluble substance and dissolves, thereby dissolving the unexposed portion, and the dry film of the exposed portion is not dissolved.

Control points:

a. Development speed (1.5-2.2m/min), development temperature (30+/-2°C)

b. Development pressure (1.4-2.0Kg/Cm2), developer concentration (N2CO3 concentration 0.85-1.3%)

Etching

OBJECTIVE: To etch away the exposed copper after using the liquid to form an inner layer pattern.

Main raw material: etching liquid (CuCl2)

Inner layer etching principle: In the inner layer pattern transfer process, D/F or ink is used as anti-etching, anti-plating or anti-etching, so most of the choices are acid etching (dry film/wet film covering the surface of the circuit pattern) To prevent copper etching: other copper that is not exposed on the substrate will be removed by chemical reaction to form the desired wiring pattern, and the wiring pattern is etched and then dried with sodium hydroxide solution/wet film)

Frequently Asked Questions: Unclean etching, excessive etching, young lines, open circuits, short circuits

Control points:

a. Etching: speed, temperature (48-52 ° C), pressure (1.2-2.5Kg / cm2)

b. Ejection: 44-54 ° C, 8-12% NaOH solution

Stripping

Purpose: Use a strong base to peel off the resist layer of the copper surface to expose the line pattern

Main raw material: NaOH