PCB production process

 

 

1. Role of PCB

PCB:

Printed circuit board; Short for: PCB Chinese: PCB

(1) On the insulating substrate, according to the predetermined design, a printed circuit, a printed element or a conductive pattern formed by a combination of the two are made, which is called a printed circuit....

(2) On the insulating substrate, the conductive pattern of electrical connection between elements and devices is provided, which is called printed circuit.

(3) The finished board of printed circuit or printed circuit is called printed circuit board or printed circuit board, also known as printed board....

PCB roles:　　

PCB is an assembly base provided for the completion of the first-level components and other electronic circuit parts, and is assembled into a module or product with specific functions.

Therefore, PCB plays the role of connecting all functions in the whole electronic product. Therefore, when the functions of electronic products fail, the PCB is often the first to be suspected. Moreover, because the processing technology of PCB is relatively complex, the production control of PCB is particularly strict and important.

2. Evolution of PCB

1. As early as 1903, Mr. Albert Hanson (Albert Hansen) pioneered the use of the concept of "line" (Circuit) to the telephone exchange system.

, it is cut into line conductors with metal foil, which is glued to paraffin paper, and a layer of paraffin paper is also glued to it, which has become the prototype of today's PCB structure.

As shown in the following figure:

2. By 1936, Dr Paul Eisner (Paul Eisner) really invented the PCB manufacturing technology and issued a number of patents.

and today's processing technology "graphics transfer technology (photoimage transfer)" is based on its invention.

3. Classification of PCB

PCB diversification in materials, layers and processes to suit different electronic products and their special needs.

. The following is a summary of some common differences to briefly introduce the classification of PCB and its manufacturing process.

a. by material

a. organic materials

phenolic resin, glass fiber/epoxy resin, Polyimide, BT, etc. belong to it.

B. Inorganic materials

aluminum substrate, copper substrate, ceramic substrate, etc. belong to it, mainly taking its heat dissipation function.

B. Distinguish the finished product by soft and hard.

a. Rigid PCB

B. flexible board Flexible PCB is shown in fig. 1.3.

c. Rigid-Flex PCB is shown in fig. 1.4.

c. divided by structure

a. single panel see figure 1.5.

B. double-sided panels are shown in figure 1.6.

c. Multilayer panels are shown in Figure 1.7.

1.3

1.4

1.5

1.6

1.7

1.8

4. Introduction to the PCB process

, we take the process flow of multi-layer board as the lead of PCB process introduction, and select the graphic electroplating process to explain the process. It is specifically divided into eight parts for introduction. The classification and process are as follows:

A. Introduction to the internal wiring process

Process introduction:

:

1. Make the inner circuit by using the principle of graphic transfer.

2. DES is developed, etched, and de-film connection.

Inner Wiring-Introduction of Material Opening

BOARD CUT:

:

• , according to the planning requirements of the pre-production design, cut the substrate material into the required working size.

• : copper clad laminate

copper clad laminate is formed by pressing copper foil and insulating layer. According to the requirements, there are different plate thickness specifications. According to the copper thickness, it can be divided into H/H;1oz/1oz;2oz/2oz and other types

precautions:

• to avoid the edge burrs affecting the quality, after cutting edge grinding, fillet processing.

• considering the influence of expansion and contraction, the cutting board is baked before being sent down the process.

• cutting must pay attention to the direction of warp and weft consistent with the engineering instructions to avoid warping and other problems.

Internal wiring-Introduction to Preprocessing

processing (PRETREAT):

:

• remove pollutants on the copper surface and increase the roughness of the copper surface to facilitate the subsequent film pressing process.

Main Consumable Material: Brush

Inner Circuit-Pressing Film

pressed film (LAMINATION):

:

• , the treated copper surface of the substrate is pasted with a dry anti-corrosion film by hot pressing.

Main production materials: Dry Film

process principle:

Introduction to Exposure of Inner Wiring

exposure (EXPOSURE):

:

• the image on the original film is transferred to the photosensitive base plate by light irradiation.

: film/film

process principle:

• the white light-transmitting part undergoes photopolymerization reaction, while the black part does not react because it is opaque. The part that reacts during development cannot be dissolved and remains on the board.

Inner Wiring-Development Introduction

development (DEVELOPING):

:

• use lye to wash out the dry film that has not undergone chemical reaction.

Main Production Material: K2CO3

process principle:

• uses the dry film that has not undergone the polymerization reaction to be washed away, and the dry film that has undergone the polymerization reaction is retained on the board as a protective layer for etching.

Description:

• water-soluble dry film is mainly due to its composition containing organic acid roots, which will react with weak bases to make salts of organic acids, which can be dissolved by water and reveal the figure.

Introduction of Inner Circuit-Etching

etching (ETCHING):

:

• use liquid medicine to erode the exposed copper after development to form an inner line pattern.

: etching solution (CuCl2)

Introduction of Inner Circuit-Film Withdrawal

removal (STRIP):

:

• use strong alkali to peel off the anti-corrosion layer of the protective copper surface to expose the line pattern.

: NaOH

Inner Line-Punching Introduction

punching:

:

• CCD is used to flush out the positioning holes and rivet holes for inspection operations.

main production materials: drill knives

inner layer inspection process

AOI test:

are all called Automatic Optical Inspection, automatic optical detection

:

• feeds back the image to the equipment for processing through the principle of optical reflection, and compares it with the set logic judgment principle or data graph to find out the defect position.

precautions:

• Because the test method used by AOI islogical comparison, there must be some shortcomings of misjudgment, so it needs to be confirmed manually.

B. Laminated drilling process introduction

Process introduction:

:

lamination: Copper foil, semi-cured sheet (Prepreg) and browned inner circuit board are pressed into multilayer board.

drilling: drill through holes for line connection between layers on the board surface.

Lamination Process-Introduction to Brown

browning:

:

(1) Roughening the copper surface to increase the contact surface area with the resin

(2) Increase the wettability of copper facing flowing resin

(3) passivate the copper surface to avoid adverse reactions

: browning liquid MS100

precautions:

• The browning film is very thin, and it is very easy to wipe flowers. Pay attention to the operation gesture during operation.

Laminating Process-Riveting

riveting

Purpose: (Four-layer board without rivets)

• , rivets are used to nail multiple inner laminates together to avoid interlaminar slippage during subsequent processing.

: rivets; Semi-cured sheet (P/P)

P/P(PREPREG):

consists of resin and glass fiber cloth,

types of glass cloth can be divided into 106, 1080, 3313, 2116, 7628, etc.

resins can be divided:

Class A (completely uncured); Class B (semi-cured); Class C (fully cured) three categories, all of which are P/P in the B- order state used in production.

Laminating Process-Introduction to Laminating

stack:

:

• the pre-stacked plates are stacked into multi-layer plates to be pressed.

: copper foil and semi-cured sheet

plating copper sheet; According to thickness, it can be divided

1/3OZ = 12um (code T)

1/2OZ = 18um (code H)

1OZ = 35um (code 1)

2OZ = 70um (code 2)

Laminating Process-Pressing Introduction

pressing:

Objective: To press the laminated plates into multi-layer plates by hot pressing.

main auxiliary materials: kraft paper and steel plate

Lamination Process-Post-treatment

post-processing:

:

• , the laminated plate is edged; Target shooting; Preliminary shape treatment is carried out in the process of edge milling so as to control the production quality requirements of the post-process and provide tool holes for post-process processing.

: drill bit; Milling cutter

Drilling Technology-Introduction of Drilling

drilling:

:

• to drill through holes for line connection between layers on the board surface

: drill bit; Cover plate; Pad plate

drill bit: tungsten carbide, cobalt and organic adhesive

cover plate: mainly aluminum sheet, which is used for bit positioning in the manufacturing process; Heat dissipation; Reduce hair head; Anti-pressure foot crushing effect

backing plate: mainly composite plate, which protects the drilling rig table in the manufacturing process; Anti-outlet hair head; Reduce the temperature of the drill needle and clean the glue and slag of the drill needle groove.

C, hole metallization process introduction

Process introduction

:

• metallize the resin and glass fibers of the non-conductive part of the hole wall

• is convenient for the subsequent electroplating process to provide sufficient conductive and protective metal holes.

Copper Sedimentation Process-Deburring and Gum Removal Slag

Deburr:

burr formation: uncut copper wire and uncut glass cloth at the edge of the hole after drilling

deburring: to remove holesburrs on the edges to prevent bad plating holes

important raw material: grinding brush

de-gluing slag (Desmear):

the reason for the formation of glue slag: the high-temperature glass transition temperature (Tg value) caused by drilling is formed into a molten state, resulting in glue slag

de-gluing slag is to expose the copper rings that need to be interconnected in each layer, and another leavening agent can improve the hole wall structure and enhance the adhesion of electroplated copper.

important raw material: KMnO4 (glue remover)

chemical copper (PTH)

chemical copper: chemical copper with a thickness of 20-40 microinches is deposited on the surface by chemical deposition.

hole wall change process: as shown in the following figure

chemical copper: as shown in the following figure

Chemical Copper

hole wall change process

Electroplating Process-Introduction of Electroplating Copper

copper once

copper once: plating copper with a thickness of 200-500 microinches to protect chemical copper with a thickness of only 20-40 microinch from hole breakage caused by post-process damage.

Important Production Material: Copper Ball

D. Introduction to the Process of Outer Dry Film

Process introduction:

:

• drilling and through-hole plating, the inner and outer layers are connected. This process makes an outer dry film to provide graphics for the production of outer circuits.

Outer Layer

processing:

Objective: To remove pollutants on the copper surface and increase the roughness of the copper surface so as to facilitate the film pressing process.

Important Material: Grinding Brush

pressed film (Lamination):

Purpose: To make the dry film tightly attached to the copper surface by hot pressing.

Important Material: Dry Film

Outer Dry Film-Introduction to Exposure

exposure (Exposure):

Objective: To expose the required circuit on dry film by pattern transfer technology.

important raw material: negative

outer dry film-DevelopmentIntroduction

development (Developing):

Objective: To rinse off the areas where the polymerization reaction has not yet occurred with a developer, and the photosensitive part cannot be washed off due to the polymerization reaction and remains on the copper surface to become an etching or electroplating inhibitor film.

: weak alkali (K2CO3)

E. The process of the outer line.

Process introduction:

:

plating the copper thickness to the thickness required by the customer.

the line shape required by the customer.

Outer Circuit-Electroplated Copper

secondary copper plating:

Purpose: The thickness of the exposed copper surface after development is added to achieve the copper thickness required by the customer.

Important Material: Copper Ball

tin plating:

Objective: To apply a layer of tin protection on the surface of secondary copper plating as a protective agent during etching.

Important Material: Tin Ball

Outer Circuit-Alkaline Etching

film withdrawal:

Objective: To strip the dry film for anti-electroplating purposes with liquid medicine.

: film removal liquid (NaOH)

line etching:

: Erosion of copper in non-conductive parts

important production materials: etching solution, ammonia water

Outer Line-Introduction to Tin Withdrawal

:

is to strip the protective tin of the conductor part.

Important Production Material: HNO3 Tin Withdrawal Solution

F. Introduction to Silk Screen Process

Process introduction:

:

the protective layer of the outer circuit to ensure the insulation, protective plate and anti-welding of PCB.

Create a character identifier.

Screen Printing Process-Introduction of Soldering Resistance

Solder Mask

solder resist, commonly known as "green oil", in order to facilitate naked eye inspection, more green pigments that are helpful to eyes are added to the main paint. In fact, there are yellow, white, black and other colors besides the green solder resist paint.

purpose

A. Soldering Resistance: Leave the through holes to be welded on the board and their pads to cover all lines and copper surfaces to prevent short circuits caused by wave welding and save the amount of solder.

B. guard plate: to prevent moisture and various electrolytes from oxidizing the circuit and endangering the electrical performance, and to prevent external mechanical damage to maintain good insulation on the board surface.

C. Insulation: As the board is getting thinner and thinner, the line width distance is getting thinner and thinner, so the insulation problem between conductors is highlighted day by day, which also increases the importance of insulation performance of anti-welding paint.

Soldering Resistance Process Flow Chart

Introduction of Soldering Resistance Process-Pretreatment

 

Objective: To remove surface oxides, increase surface roughness and strengthen surface ink adhesion.

Main Raw Material: Volcanic Ash

printing

: Use silk screen to write ink printing on the board, as shown on the right:

Main Raw Material: Ink

:

A Print (Screen Printing)

B shower type (Curtain Coating)

C spray Coating

D Roller Coating

Introduction of Soldering Resistance Process-Pre-drying

pre-baked

Objective: To drive away the solvent in the ink and harden the ink part so as not to stick the negative during exposure.

Process Points

temperature and time must refer to the conditions provided by the supplier. The pre-baking conditions for double-sided printing and single-sided printing are different.

oven must pay attention to ventilation and filtration system to prevent foreign matter from sticking.

the setting of temperature and time, there must be an alarm, and it must be taken out as soon as the time arrives, otherwise over curing will cause incomplete development.

Introduction of Soldering Resistance Process-Exposure and Development

exposure

Purpose: Image transfer

main equipment: exposure machine

Process Points:

A Exposure Machine

B Energy Selection

C vacuumingcontrol

development

Objective: To remove unpolymerized photosensitive ink with 1% potassium carbonate solution.

: potassium carbonate

Character Technology-Introduction to Printing

 

Purpose: To facilitate maintenance and identification

Principle: Screen Printing

main production materials: text ink

Description of Character Process-Curing

Cure (Post Bake)

Objective: To completely harden epoxy resin in ink by baking at high temperature.

G. Introduction to Selection of Surface Technology

conventional printed circuit boards (PCB) have a copper layer on the board. If the copper layer is not protected, it will be oxidized and damaged, which will directly affect the subsequent welding.

, the most common ones are: hot air leveling (HASL), organic coating (OSP), electroless nickel gold (plating gold), electroless nickel gold (ENIG), gold finger, silver (IS) and tin (IT), etc.

(1) Hot Air Leveling (HASL): After the board is completely covered with solder, the excess solder in the surface and hole is blown off by high-pressure hot air, and the solder attached to the pad and hole wall is leveled; There are two types of lead-sprayed tin and lead-free sprayed tin.

advantage: low cost and weldability throughout the manufacturing process.

(2) Organic Coating (OSP): A thin, uniform protective layer is formed on the copper surface of the PCB.

advantages: comparable to HASL in cost, good coplanar, lead-free process.

(3) plating gold plating: nickel and protective layer gold are plated on the copper surface by electroplating.

advantages: good weldability, flat surface, long storage life, can withstand multiple reflow soldering.

(4) Chemical nickel-gold (ENIG): replace the nickel-phosphorus layer on the copper surface through chemical reaction, and then replace a layer of gold on the nickel layer.

advantages: good weldability, flat surface, long storage life, can withstand multiple reflow soldering.

(5) Gold Finger: Nickel and gold are plated on the same surface by electroplating, because gold plating contains other metal differences (3).

(6) Sinking Silver (IS): Silver is immersed in the copper layer and 0.1 to a 0.6 micron metal layer to protect the copper surface.

advantages: good weldability, flat surface, natural replacement of HASL immersion.

(7) Sinking Tin (IT): Tin is immersed in the copper layer and 0.8 to a 1.2um metal layer to protect the copper surface.

advantages: good weldability, smooth surface and relatively low cost.

H. Introduction to the process flow of the post-process.

Process introduction:

:

• Complete the processing according to the customer's appearance.

• tested according to the requirements of electrical performance.

• Do the final quality check before shipment.

Process Flow Introduction of Post-process Shape

shape

Purpose: To cut the board into the specifications and sizes required by customers.

Principle: Digital Machine Tool Mechanical Cutting

• -Main Production Material: Milling Cutter

Process Flow of Electrical Measurement in Post-operation

electrical measurement

Purpose: To test the bare board of PCB's electrical performance, I .e. open and short circuit, to meet customer requirements.

electrical measurement:

A. Special Machine (dedicated) Test

advantage: fast production speed

Disadvantages: The test needle cannot be recycled and the jig cost is high.

B. Universal on Grid test

advantage: a jig cost is lower

Disadvantages: A equipment is twice as high

C. Moving probe

do not need to make expensive jigs, use two probes to move x, y and z to test the two ends of each line one by one.

advantage: no jig is required and the cost is low.

Disadvantages: Low efficiency.

Final Inspection/Laboratory Introduction

final test/laboratory

Purpose: Final inspection/laboratory is the final quality check in the process.

(1) Main items of inspection:

1 Overall Dimension Outline Dimension

2 Hole to Edge for each size

3 Board Thickness

4-aperture Holes Diameter

5 Line width/space

6-hole ring size Annular Ring

and other items in appearance and length!

(2) The main laboratorykey items:

1. Solderability Solderability

2. Line peel strength Peel strength

3. Slice Micro Section

4. Thermal shock Thermal Shock

5. Ionic Cont.amination

6. Moisture and insulating Moisture and Insulation Resistance

7. Impedance Impedance

and other reliability projects.

PCB flow diagram

 

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