Surface Mount Technology Basics

2013-06-16 23:55:06 12

 

Surface Mount Technology Basics
◆ SMT features
High density assembly, electronic products small size, light weight, chip component size and weight of traditional plug-in component of about 1/10, the general use of SMT, electronics volume reduced 40% to 60%, 60% weight 80%.
High reliability, strong anti-vibration. Solder joint defect rate.
Good high frequency characteristics. Reduces electromagnetic and radio frequency interference.
Easy to automate, improve production efficiency. Reduce costs by up to 30% to 50%. Saving materials, energy, equipment, manpower and time.
◆ Why use surface mount technology (SMT)?
Miniaturization of electronic products to pursue, previously used perforated plug element has been unable to reduce
More complete electronic product functions, using integrated circuit (IC) has no perforation components, especially large-scale, highly integrated IC, had to use surface mount components
Product batch, production automation, factory to a low cost high yield, produce high-quality products to meet customer demand and enhance market competitiveness
Development of electronic components, integrated circuits (IC) development of semiconductor materials for application
Electronic technology revolution is imperative, chase international trends
◆ Why use surface mount technology (SMT)?
Miniaturization of electronic products to pursue, previously used perforated plug element has been unable to reduce
More complete electronic product functions, using integrated circuit (IC) has no perforation components, especially large-scale, highly integrated IC, had to use surface mount components
Product batch, production automation, factory to a low cost high yield, produce high-quality products to meet customer demand and enhance market competitiveness
Development of electronic components, integrated circuits (IC) development of semiconductor materials for application
Electronic technology revolution is imperative, chase international trends
◆ Why is the surface mount technology-clean processes?
Production process the wastewater after the cleaning products, bring water, land animals and plants as well as pollution.
In addition to water washing, the application of an organic solvent containing chlorofluorocarbons (CFC & HCFC) for cleaning, but also on the air, the atmosphere of pollution, destruction.
Cleaning agent remains in the machine to bring the board corrosion, seriously affecting product quality.
Cleaning process to reduce operating costs and machine maintenance.
Free cleaning can reduce the group board (PCBA) in the process of moving and cleaning the damage. There are still some elements bear to clean.
Flux residues under control, with the appearance of the product requirements can be used to avoid visual inspection of the clean state of the problem.
Residual flux has continued to improve its electrical properties, in order to avoid product leakage, cause any harm.
Disposable flow has passed a number of international safety tests to demonstrate the flux of chemical substances is stable, non-corrosive
◆ Reflow soldering defect analysis:
  Tin beads (Solder Balls): Reason:
1, screen printing and pad hole right position, printing imprecise, making paste dirty PCB.
2, paste in an oxidizing environment too much exposure, smoking too much moisture in the air.
3, the heating inaccurate, slow is not uniform.
4, the heating rate is too fast and the preheat zone.
5, paste dries too fast.
6, the flux activity is not enough.
7, too many small particles of tin powder.
8, volatile flux during reflow inappropriate. Solder ball is recognized standards process: When the pad or printed wire when the distance between 0.13mm tin bead diameter must not exceed 0.13mm, or can not appear within 600mm square tin beads over five.
Bridging (Bridging): Generally, causing bridging factor is due paste too thin, including the metal paste or solid content is low, thixotropic low, solder paste is easy to squeeze open, solder particles too large, flux Surface tension is too small. Pad too much solder paste reflow peak temperature is too high and so on.
Open (Open): Reason:
1, the solder paste volume is not enough.
2, component lead coplanarity enough.
3, tin wet enough (enough to melt fluidity bad), causing solder paste is too thin loss.
4, the pin suction tin (the same as rushes) or near the connection holes. Pin coplanarity for fine pitch and ultra-fine pitch leaded components is particularly important, a solution is on the pad in advance on the tin. Pin suction tin can slow down the rate of heating and bottom heating and more, at least to prevent heating. Can also be soaked in a slow, high temperature flux activity or in a Sn / Pb in different proportions to reduce blocking molten solder pin suction tin.
◆ SMT related technical composition
Electronic components, integrated circuit design and manufacturing technology
Electronic circuit design techniques
Circuit board manufacturing technology
Automatic placement equipment design and manufacturing technology
Circuit assembly manufacturing technology
Assembly auxiliary materials used in the manufacture, development and production technology
◆ Mounter:
  Gantry-type (Gantry):
Component feeders, board (PCB) is fixed, the placement head (install multiple vacuum suction nozzle) in the feeder moves back and forth between the substrate and the component removed from the feeder, the position and orientation of the component after the adjustment, then placement on the substrate. Post titles are mounted on the gantry-type X / Y coordinates moving beam, so named.
Position and orientation of the component adjustment method:
1), adjust the position of mechanical alignment, adjust the direction of rotation of the nozzle, this approach can achieve the accuracy is limited, do not use the later models have.
2), laser identification, X / Y coordinate system to adjust the position, adjust the direction of rotation of the nozzle, this approach can achieve recognition during the flight, but not for ball grid columns Chen element BGA.
3), the camera recognizes, X / Y coordinate system to adjust the position, adjust the direction of rotation of the nozzle, usually a fixed camera, camera placement head flying across the sky, imaging recognition, than laser wasted little time recognition, but can identify any element, there are achieved during the flight identification of camera recognition system, there are other aspects of the mechanical structure sacrifice.
This form of the placement head moves back and forth in a long distance, the speed is limited. Now generally use multiple vacuum suction nozzle while reclaimer (as many as ten), and dual beam system to improve the speed, that is, a beam attached to titles in reclaiming the same time, another beam placement stickers titles element, the speed is almost twice as fast than the single beam system. But the practical application, while reclaiming the condition more difficult to achieve, and different types of components needs to be replaced with a different vacuum suction nozzle for suction nozzle to a time delay.
The advantage of these models: the system structure is simple, can achieve high accuracy, suitable for a variety of sizes, shapes, components, and even shaped components, feeders with ribbon, tube, tray form. Suitable for small batch production, can also be a combination of multiple machines for large volume production.
Turret type (Turret):
Component feeders placed in a single coordinate movement of the material on board, board (PCB) placed in an X / Y coordinate system moving workbench placement head mounted in a turret, work, skip the component feeders Move to reclaimer location, placement head vacuum suction nozzle in a position to take elements reclaiming by the turret rotates to patch location (the location and reclaimer 180 degrees), during rotation through the position and orientation of the component adjustment of the component placement on the substrate.
Position and orientation of the component adjustment method:
1), adjust the position of mechanical alignment, adjust the direction of rotation of the nozzle, this approach can achieve the accuracy is limited, do not use the later models have.
2), the camera recognizes, X / Y coordinate system to adjust the position, adjust the direction of rotation of the nozzle from the camera fixed camera placement head flying across the sky, imaging identification.
In general, is mounted on the turret a few dozen to twenty titles affixed, the head of each patch installed 2 to 4 vacuum nozzle (older models) to 5 ~ 6 vacuum nozzle (current models). Because the characteristics of the turret, the action miniaturized toggle nozzle, feeder moves into place, taking components, component identification, angle adjustment, table moves (including position adjustment), attached components such action can be put in the same time period complete, so to achieve a real sense of speed. Currently the fastest time period reaches 0.08 to 0.10 seconds, an element.
This model is superior in terms of speed, suitable for mass production, but it can only band-shaped packaging element, if it is fine pitch, a large integrated circuit (IC), only the tray packaging can not be completed, it is also depends on other models to work together. The device structure is complex, expensive, latest models around US $ 50 million, is more than triple arch type.
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