SMT process technical problems
SMT, surface-mount Technology Surface Mount Technology
SMC - Surface Mount component Surface Mount Componet
SMD - Surface Mount Device Surface Mount Device
SMB - Surface Mount PCB Surface Mount Printed Circuit Board
THT - through hole interpolation technology
MSI - medium scale integrated circuit
LSI - large-scale integrated circuit
The advantages of SMT
The products of the 1yuan pieces are of high value and light weight.
The strong resistance is strong.
High frequency is very good.
It is easy to be effective and effective.
5 can reduce the cost.
Eight major technical problems of SMT management engineering test material equipment process substrate graphic design of components.
The conditions of a tin plaster
Solder paste is a paste made of alloy solder powder, paste flux and some additives
The shape of body. It is a homogeneous, stable mixture. At the same time, the electronic components of the electronic components will be placed in a paste
Heat to a certain temperature when as evaporation of solvent and some additives, alloy melting reflow solder paste made by welding components and solder interconnection
A solder that is cooled to form a permanent connection.
It is a good idea to have a good printable and resoled solder
Stability.
The welds need to be specific
1, with long storage life is saved in 2 ~ 5 degrees when storing 3 ~ 6 months will not change chemical also won't appear the solder powder
And the welding of the present and separation of the present and the adhesion and adhesion.
2, small hygroscopicity, low toxicity, odorless, non corrosive.
2. It is very special in the application of the application.
1, good printing and drop with sexual membranous off good can continuous smooth coating not clogged screen or leakage of plate
Kong eye and the injection of the mouth of the mouth are not to be spout.
2, have longer working life luck usually required after printing or drop in room temperature can be placed 12 to 24 hours its performance remains the same.
3, during reflow soldering preheating solder paste should keep its original shape and size does not produce damage. Collapse refers to a certain volume of solder paste
after printing or drops on PCB due to the effect of gravity and surface tension and temperature increase or reduce the height of parking time is too long and cause
The present situation of the end of the boundary is called a collapse.
3. Characteristics of reflow welding with heating
1, good wettability. The preparation and preparation of the preparation of solder and wetting preparation should be used for the purpose of wetting and wetting.
2, solder splash will not occur. It is mainly depended on the water absorption of solder paste, the type of solvent in solder paste, boiling point and dosage and solder powder
Type and content of impurity.
3, formation, the least amount of solder ball.
The characteristic of recurrent welding
1, better ensure that will not happen due to factors such as vibration strength of welding components fall off.
2 residues after welding stability performance is good non-corrosive have higher insulation resistance and good cleaning.
2 , affect solder paste properties of some important parameters
1 viscosity
The welding paste is a kind of fluid to be able to be able to use the power of the external force to produce the power of printing and re-flow-welding.
Welding paste in printing time from the beginning of the use of the blade pressure of the use of the blade pressure
Degree of state to leave accurate graphic on the PCB.
2 the alloy solder powder composition, ratio and the content of flux
The composition of solder powder and flux in solder paste and the matching of the two are greatly affected.
Alloy welding powder is the main component of the paste in the area of the paste heavy weight of 85%~ 90%. Several kinds of tin-used solder powder
- lead Sn Pb , tin, lead, silver Sn Pb - Ag , tin, lead, bismuth Sn Pb - Bi , etc. The most commonly used alloy components are
Sn63 / Pb37 and Sn62 / Pb36 / hf-solvated Ag2 Sn63 / Pb37 of melting point is 183 ℃ eutectic state melting point is 179 ℃ after mixed with 2% of silver
There is a good and good physical characteristic and good quality of welding
Mechanical strength of solder joints.
3 melting point
Sn63 / Pb37 -- -- -- -- -- 183, Sn62 Pb36 / hf-solvated Ag2 -- -- -- -- -- 179, Sn43 Pb43 / Bi14-114 ~ 163, Sn96.5 / Ag3 Cu0.5-217
4. The form and granularity of the alloy powder
In order to avoid the oxidation of tin powder need spherical powder because the area of the spherical minimum area within a certain capacity is the smallest. And at the same time
The spherical volume manufacturing bulky can reduce the scope of the oxidized. The common use of particle size 20~ 45umis to be more and more delicate
Type of body welding trend is bound orientation of powder particle size distribution more narrow, more fine powder.
Usually the size of the tin powder is a thickness of about a third has to print the following and plate opening of about one 5 of the minimum range of the following most
As the standard. But the smaller the particle size also has its disadvantages (1) with a total area of the larger easy oxidation 3. (2) than a fine solder balling extension and after welding
Less intense.
5 contact and collapse
1) the metal content is much higher than 90%
The time can be changed and the collapse of the paste is filled with the solder
The effective anti-stop tin ball for the effective anti-stop tin ball is the printing and welding
The process requirements are stricter. Metal content is smaller than 85%
The printing of good and wettable, but the lack of a point is the collapse of the silosphere and the short road.
6 working life and storage life
3 welding agent
The use of the solder is required
The effect of flux (1) to remove oxide on the surface of the metal and small acidification (2) covering the heating of the metal surface prevent oxidation 3 again
The surface tension of the soldering flux.
And the essential thing is
A solder and solder alloy powder is mixed evenly.
B is to use high boiling point solvent to prevent and refloat the product.
(c) high adhesion and welding powder and soldering preparation.
(d) low absorption and moisture protection against the splats of the steam.
(e) low chloride content.
2 welding preparation
Active agent, film former, wetting agent, stabilizer and solvent to improve adhesion, thixotropy and printing also need to add adhesive,
Thickening agents, thixotropic agents and other additives. The composition of solder is extensibility, wettability, collapse degree, viscosity change, cleaning and bead
Splash and storage life have a great impact.
1-2 lowering the surface tension of the tin
1-3. The internal surface of the net is low
2-1 to remove oxide film reactive temperature > 100 degrees
3-1printing time internal mechanical pressure resistance
3-2adhesive reply
The time and time of the inner surface of the net of 3-3 steel paste is low
High temperature resistance
4-1adhesion time internal retention boiling point 220-290degrees
4-2 SHELF LIFE to keep
The solder can be solderable in 50%-60%
The surfactant is 10% weldable
Conformal agent 15% printing is effective
Solvent 15-25%
The same kind of preparation and cleaning
1 inorganic flux need clean water to wash, hot water washing
Flux resin rosin R class 2 without cleaning
Mild active RMA does not require cleaning
Cleaning solvent should be cleaned
High activity RA class needs cleaning solvent cleaning
3 water-soluble flux need clean water to wash, hot water washing
High boiling point solvent
The use of high boiling point solvent and increase of content can cause soldering in solder paste.
The temperature should be higher and higher in the square method
B warm-up time
The peak temperature of c increases
D high moisturizing cream
Printing matters
1. The printed sheet is attached to the surface of the substrate and the printing requirements of 0.1mmms are required
0.15mmmminterplay to prevent the removal of the defects and the need for slow printing.
2. The blade will be processed and repaired at the same time.
3. The surface of the board is applied to the electrode with a soft cloth and a soft cloth
The surrounding area produces tin balls.
4. In the front and rear of the printing time, the base board must be the base plate
The two ways to make up the law are to shift the printing of the printing and the auxiliary board.
Six ways of doing things
1, will stored in the refrigerator 2 ~ 10 ℃
The mixture of tin powder and liquid soldering preparation is the product of chemical change. so
It is necessary to release the products in cold storage.
2, frost of solder paste to place 4 ~ 8 hours at room temperature make it back to normal temperature before open.
Solder paste is used by most avoid moisture flux rosin, low solvent, resistance to moisture absorption and foreign water spillage caused solder ball
Bad phenomena.
3, open after use stainless steel rods stirring about 2 minutes to make it even and increase the activity of the solder paste.
4, general solder paste dosage depends on the printing area size. It is not important to have a lot of free and free splattering
The end of the world is well - done. Keep the tin cover in place and set aside for standby.
5, fill quantity to was about to call it a day going to don't still retained too much solder paste on the print.
Collect the work to prepare for another empty bottle collection printing machine. The propellant of the tin-plaster was overturned and overturned
The machine will absorb the air and gas in the air, and lose the maximum amount of time. yeah
In the use of recycled tin-plaster to mix with the mixture of the new 2old 1.
6 collection and receiving of tin paste method
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