Screen printing technology in PCB production process has been in application, not only only is a single panel, double panel and the transfer of multilayer PCB circuit graphics, resistance welding flux, character symbol adopted the silk screen printing process.With the growth of the economic skills, increasingly demand improvement product precision and pass rate of guaranteeing the product quantity, low capital, thus obtains the good economic benefit.Than to precision line also accept screen printing craft, and has high position accuracy.In this paper, the credentials of the silk screen printing the things my resume, for screen printing process held many factors influencing screen printing precision PCB, so how to progress screen printing precision?This this paper puts forward some opinions on how to advance accuracy, to cooperate to explore.
And the influencing factors of silk screen printing precision
PCB printing patterns that include the following two aspects: one is the graphic line amplitude distortion degree to small, precision of line width 0.05 mm;2 refers to the printed graphics location accuracy requirement is high, the graphic length is 500 mm, inside position problem < 0.15 mm, affects the accuracy of the above-mentioned two aspects has a variety of factors, from screen plate to the graphics printing production process, important factor has the following several aspects:
1. The screen plate making the choice of the material and printing materials: bag net frame material, silk screen material, mesh, color, and printed material performance;
2. Screen printing set equipment deployment, tooling: namely the silk screen printing machine, positioning jig, etc.
3. The production process includes stretch mesh, screen plate making, printing process, etc.;
4. What environmental conditions: things garden of temperature, humidity, cleanliness, especially cleanliness are the important factors that affect product case quantity;
5. Who is the most important factors affecting the quality of engineering, the operator must have a high sense of responsibility and high skills essential.
Before this focus on several aspects of the effect of factors on the printed graphics printing the principle and progress of the pace of the precision and the main point.
Second, the progress screen stencil quality is the condition of guaranteeing screen printing precision
The influencing factors on the quality of the screen stencil with photography, photography, rendering quality version of the manuscript and the size of the photographic plate stability environment.Screen stencil making and involves network frame, stretched screen, plate making, and how many factors such as light sensitive material.
1. Net frame material choice as usually choose LY12, cemented carbide such as LF2 aluminum square tube profile, size selection of 20 mm wide, 20 mm thick, the four corners with argon arc welding and riveting.Metal frame of high precision, stable size.
2. Silk screen material choice with the most now is nylon mesh and polyester yarn.Nylon net heat resistance is poorer, heating thermoplastic deformation, easy pregnant before and after the tension is not symmetrical, affect the quality of screen printing.Binding tension net or screen stencil making unfavorable high temperature baking.Polyester yarn network has good heat resistance, stable size, graphics do not occur because of temperature and humidity change breeds larger changes.In order to package network printed graphics fidelity had better choose monofilament polyester yarn.At the same time, should choose high number of wire mesh, wire diameter is small, the smaller screen mesh, wire mesh color yellow or tan as well, in case of pregnant halation.
3. Stretch mesh tension net is the key to a no not seeing, to make high precision printing graphic couplet stretched network meet quality requirements, the best accept pneumatic tension net machine, stretch mesh quality requirements are as follows.
A. stretch mesh tension conform to and symmetry
Not Zhang Liyu big is better, the tension is too large, above the material elastic limit, the screen will lose elasticity, crisp and even rupture.Tension does not apply the soft silk screen, the lack of resilience.Should be according to the rated tension, and then the credential operation conditions favor thought, make its entire web pages tension symmetry.
B. graticule links as silk
Good screen geographic should be probably with vertical net frame connection, stretch when network is a wire drawing net, namely force equal to wire to link;2 it is to be net clamp clamping of the silk screen drawing can move laterally.
C. watch out for lax
In order to reduce stretch good net with the passage of time, the screen will become loose or more with more loose, landing in tension, continuous net should be accepted and repeated pull tight mesh point, make a division completed before tension lax in fixed network.
4. The screen stencil plate making process now with the most is the rule of law as a silk screen template directly, in this process carefully glue coating thickness conform to, harsh drying, exposure, development and other key control, in order to get high quality screen stencil.
Three, control various influencing factors of screen printing process, to improve screen printing precision
Now beginning to requirements during the course of screen printing graphics processing, printing material performance is excellent, the second must be strict control set printing equipment deployment, tooling, scraping board, network distance, pressure and other technological factors.
1. Printed material must meet the following properties:
Good chemical stability;The drying rate fitting for;To apply the copper foil board adhesive performance is good;Viscosity conform to, good thixotropy, color in accordance with;
Good capability to penetrate the seal;Easy to dry.
2. Set the equipment deployment tooling
Accept printing precision screen printing press can remove many unstable factors, positioning jig can directly use the machine surface longitudinal adjustable positioning pin positioning.
3. Other technological factors
Scraping board, scraping board width, hardness, Angle, edge status and network distance, scrapping printing pressure is very important, should choose polyester rubber scraper.Scraper width is proper, too wide of the graphic distortion, scraper hardness most in shore A60-80 within a category, blowing Angle of 20 ~ 30, must often link flat sharp edge.Net as usually 2 ~ 4 mm distance parallel to the surface and the screen mesh, scrapping printing pressure to print out clear graphics is advisable.
To sum up the above process factors, the important factor affected the accuracy of line graphic picture to cover printing material, scraping board hardness, edge condition, printing pressure and Angle etc, deployment and screen printing equipment, tooling, net and scraper width influence factors including the position of the printing and graphic precision, high quality screen stencil is printing precision shall be no less progress.