Reflow soldering is the main method and SMT assembly process, and solder paste is one of the most important raw material of reflow.
This welding to the needs of the welding property excellent together, these features include easy processing, wide compatibility on various SMT design, high reliability and low cost welding; however, during reflow soldering is used as the students to the SMT element and plate with each other while repeatedly, it also by further improving welding challenge, in fact, reflow soldering technology can withstand this challenge will determine the solder paste can continue as SMT processing the first welding materials, especially in the fine pitch technology progress situation. Here we will investigate the effect of improved reflow welding properties of several problems, in order to stimulate industry research new methods to solve this lesson, we separately for each problem is briefly described as follows:
Fixed plate element
Layer of reflow soldering has been used for many years, the first on the first surface printed cloth wiring, installation of components and the soft melting, and then turned on the other side of the circuit board processing, in order to save more reasons, some process eliminates the need for the first surface soft buff, but also the soft melting the top surface and the bottom surface, typical example is the bottom surface of the circuit board only small components, such as chip capacitors and chip resistor for printed circuit board (PCB) design more and more complicated, installed in the bottom of the element is also more and more big, the cohesive element loss becomes an important issue. Obviously, element shedding phenomenon is due to the soft when the melted solder melting of element is vertically fixed force, rather than the vertical fixed force can be attributed to the increase in weight of the element, element poor weldability, solder wettability or insufficient solder volume, wherein, each factor is the most fundamental reason. If the three factors on the back of the improved after shedding phenomenon for components, you must use SMT binder. Obviously, the use of binder will make the cohesive elements self-aligned effect becomes worse.
Solder false welding
Weld is the formation of welding bridge between adjacent wires. Usually, all can cause the paste off collapse factors will lead to weld, these factors include:
1, the heating speed is too fast;
2, thixotropy of solder paste is too poor or paste viscosity at a shear recovery is too slow;
3, the metal load or solid content is too low;
4, powder granularity by too much; workers
5, the flux of surface tension is too small.
But the collapse is not necessarily cause not weld fully, in the soft melting, melted not weld fully solder off may be driven by surface tension, the loss of the solder will not weld fully problem becomes more serious. In this case, the loss due to the solder gathered in a region of the excess solder will make the molten solder becomes too much and not easy to break.
In addition to causing factors of solder paste slump, the following factors are a common cause of welding discontent:
1, the relative between solder joint space, paste deposited too much;
2, high heating temperature;
3, the solder paste is faster than the circuit board;
4, solder wetting speed too fast;
5, the flux of vapor pressure is too high;
6, too high solvent content of flux;
7, the flux resin softening point is too low.
Continue to wetting
Intermittent wetting solder film is that the smooth surface, which is due to the surface of the solder can stick to a solid metal surface most,, and in the solder layer of melted hidden under some not wetted, therefore, at the beginning of the molten solder to cover the surface, there will be there continue to wetting phenomena. The molten solder metastable covering layer can be the driving force in the minimum surface under the action of will shrink, not for a while and then gather in separation of pellet and the ridge bald up. Continue to wetting can gas released by parts in the molten solder contact caused by release due. Hydration decomposition or inorganic organic hot water will produce gas. Water vapor is the gas most common ingredients in the welding temperature, water vapor has strong oxygenation effect, can the surface oxidation of molten solder film or some subsurface interface (a typical example is in the melt solder metal oxide on a junction surface). The common case is the welding temperature and longer residence times higher will lead to more intermittent wetting phenomenon is serious, especially in the base metal, increase the reaction rate will lead to more
A violent release of gas. At the same time, longer residence time will be extended gas release time. These two methods can increase the release amount of gas, eliminating method to wetting phenomenon is:
1, reduce the welding temperature;
2, shorten the length of stay in the soft melting;
3, use of inert gas flow;
4, to reduce the pollution degree.
Low residue
The reflow process without cleaning, in order to obtain a decorative or functional effect, often require low residue, on the functional requirements are examples include "to probe testing surfacing layer by the flux residue testing at the circuit and inserted between the joint and the soft melting solder joints near the through hole sleeve contact", flux residue more often result in the metal layer to electrically contact had covered much residue, establish this would interfere with electrical connection, in circuit density increase, this problem more and more attention by people.
Obviously, no clean low residue paste is to meet the requirements of an ideal solution, soft melting necessary conditions associated with this makes this problem more complicated. In order to predict welding properties in different levels of inert soft melting low residue paste, put forward 1.5 empirical models, this model predicts. With decreasing oxygen content, welding rapidly improved performance, then gradually stabilized, experimental results show that, with the decrease of oxygen concentration, the wettability and solder paste welding strength will increase, this year, the welding strength also increased with the increase of solid content in the flux. The proposed model is available experimental data comparison of strong local, and proves the validity of the model, can be used to predict the welding performance of solder paste material, and therefore, can assert that, in order to welding process successfully by using no low residue solder cleaning, should be soft melting atmosphere using inert.
Clearance
The gap is formed between the solder joint no component leads and circuit board solder joint. Generally speaking, this can be attributed to the following four reasons:
1, the solder melting problems;
2, lead coplanarity deviation; sweet green rice ball
3, wetting is not enough;
4, the solder consumption
This is the collapse of a printed circuit board pre tin solder paste, lead the wicking effect (2,3,4) through holes or solder joints near the causes, problems lead coplanarity is new lighter weight 12 mils (UM) spacing of the four core wire centralized flat circuit (QFPQuad flat packs) is a special don't concern, in order to solve this problem, proposed before assembly with solder to pre coated solder (9), this method is to expand the local dimension of solder joints and along the solder pre bulging coverage area to form a control local welding region, and thus to compensate lead coplanarity changes and prevent clearance, lead wicking effect can slow heating speed and make the bottom top heating more than to be resolved, in addition, the use of wetting slow flux, higher activation temperature can delay the molten solder paste (such as mixed solder tin powder and lead powder) can also minimize the wicking effect. Before covering light the whole circuit board with tin lead solder mask used to cover the connection path can also prevent caused by through holes near the wicking effect.
Solder balling
The solder ball is the most common and the most difficult problem which refers to the solder reflow process into different size of spherulite in not far from the main solder bath place setting; in most cases, the spheres are composed of solder powder in the solder paste, solder balling the circuit board has a short circuit and problems leakage current and welding point insufficient solder etc..
With fine pitch technology and welding method of cleaning without progress, people become more and more urgent to use non SMT process solder balling phenomenon.
Cause the solder ball (1, 2, 4, 20) causes include:
1, because the oil circuit printing process caused by the improper; cauliflower
2, the solder paste too much exposure to the oxidizing environment;
3, the solder paste too much exposure in the humid environment;
4, the heating method is not appropriate;
5, the heating speed is too fast;
6, the preheating section is too long;
7, the solder mask interaction between membrane and solder paste;
8, the flux activity is not enough;
9, welding powder oxides or excessive pollutants;
10, the dust is too much;
11, in the soft melting process specific, flux into inappropriate volatiles;
12, the solder paste formulations caused by improper solder collapse;
13, the solder paste is not fully restored to room temperature before use, open the packaging;
14, printing thickness too thick lead to "collapse" the formation of solder ball;
15, low metal content of welding in conversation.
Solder beading
Solder beading is a special phenomenon in the use of solder paste and SMT process solder balling, say simply, bead refers to those very big ball and stick with it (or not) the solder ball is small (11).
They formed in the low bracket components such as chip capacitors around.
Solder beading is caused by the flux exhaust, in cohesion preheating stage the exhaust effect is greater than the solder paste, solder paste exhaust promoted the formation of isolated granules in low clearance element, in the soft melting, isolated solder melted again emerge from the elements, and coalescence plays.
Including welding beading reason:
1, the printed circuit thickness is too high;
2, the solder joint and element much overlap;
3, in the element with excessive solder paste;
The 4 element, placed too much pressure;
5, preheating temperature rise too fast;
6, the preheating temperature is too high;
7, released from the component and solder in moisture resistance;
8, the flux of reactive too high;
9, the material used is too thin;
10, the metal load is too low;
11, the solder paste slump too much;
12, welding powder oxide too much;
13, the solvent vapor pressure is insufficient, the elimination of the most simple method of solder may be changing the pore shape, so that between the low bracket components and solder joints with less solder paste.
Welding fillet welding on
Welding fillet lifting refers to the peak after welding and fillet welding wire from four core wire flat integrated circuit has a fine circuit spacing (QFP) solder joint on completely up, especially in the element edges near the place, one possible reason is in the lead in the wave soldering machine before sampling inspection the stress, or is in the processing circuit board and be subjected to mechanical damage (12).
In wave soldering before sampling, lead a tweezers across the QFP element, to determine whether all the lead in soft melting baking are welded; the result is produced without weld toe alignment, this can be seen in the observed from top to bottom, if the heating plate in the fillet weld between interface welding zone / caused a part of the two soft melting, then, from the circuit board lifted leads and fillet weld can relieve the stress inside, one way to prevent this problem is in wave soldering after (not before wave soldering) sampling inspection.
Erect a monument
Tombstone refers to the non lead components (such as chip capacitor or resistor) is away from the substrate, and the components are supported at one end of it.
Tombstone is also known as the Manhattan effect, Drawbridging effect and Stonehenge effect, safety is a cohesive element ends caused by uneven lubrication; therefore, the molten solder is not equilibrium surface tension is applied to the element ends, with the development of the miniaturization of SMT, the electric components on this problem becomes more and more sensitive.
The reason of this situation formed:
1, uneven heating;
2 elements: shape differences, too light weight, solderability difference;
3, poor thermal conductivity substrate material, substrate thickness uniformity;
4, the heat capacity difference between the larger pad, pad solderability differences;
5, the uniformity of solder paste flux closed rib, thickness difference between two pads on the solder paste, solder paste is too thick, the printing precision, serious dislocation;
6, the preheating temperature is too low;
7, Mount precision, element migration serious.
Ball Grid Array (BGA) into the ball side
BGA ball most often as not weld fully, not at the solder ball, solder ball leakage, and insufficient solder defects, this is usually due to the lack of fixed force on the sphere of soft melting or self force.
Fixed capacity may be low viscosity, high barrier thickness or high gas velocity caused; and self force is insufficient in general by the welding flux of low activity weak or solder volume too low and cause.
BGA ball effect can be achieved by using solder paste alone or the solder balls are used in conjunction with the solder and solder ball and flux to achieve; feasible method is correct and overall preform flux or solder paste with the use of.
The most common approach appears to be the solder balls are used in conjunction with the solder paste, tin ball forming process using 62 or 63 ball bonding has an excellent effect.
In the use of flux to 62 tin or tin ball 63 welding, defect rate with the flux decrease viscosity, volatile solvent and pitch size increases, but also with the cladding thickness of flux, solder and solder joint activity increases in diameter in the solder paste used for high temperature molten ball bonding in the system, there was no solder ball leakage phenomenon, and the accuracy with the solder paste deposition thickness and the flux of volatile, the flux of reactive, solder joint size and can increase the welding and metal load increases, in the use of 63 tin solder paste, solder paste viscosity, effects of distance and soft melting section on the ball a few autumn no high melting temperature.
In the release process using conventional printing, easy release of the solder paste to paste into a ball is crucial to separate.
Ball forming process overall preform is promising.
Reduce the width and thickness of solder link is also very important to improve the success rate of the ball.
The formation of false welding
The formation of pores is usually a related problem and welding joint.
Especially when the application of SMT technology to reflow solder paste, the leadless ceramic chip case, the vast majority (0) of pore.
The 0005 inch /0.
01 mm) is in between the LCCC pad and the printed circuit board solder joints at the same time, in the vicinity of LCCC castle like the corner, only very small amounts of small pores, pores will affect the mechanical properties of the welded joint, and will damage the joint strength, ductility and fatigue life, which is caused by the damage the reason. In addition, the solder will shrink in solidification, welding plated through hole when the stratified exhaust and entrainment flux is caused by the pore.
In the process of welding, forming pore mechanical system is more complex, in general, the pore is exhaust gas entrainment flux sandwich like structure in the solder reflow time caused by (2,13) determines the solderability of pore formation is mainly composed of metallized area, and with decreasing flux activity, increase coverage powder metal load increase and lead connector under the changes, reduce the solder particle size can only slightly increase the pore. In addition, pore formation and accumulation and the junction of solder powder to eliminate the time allocation between the fixed metal oxides. Solder paste coalescence more dry, more often the pore forming. Large pore ratio, increase with the total pore volume increased, compared the analysis results with the total pore volume of the situation, the formation factors will have a greater impact on the reliability of welded joint of illuminating, including the way to control the pore formation:
1, improve the element / jacket bottom weldability;
2, using the higher rib welding flux;
3, reduce the solder oxide;
4, the inert heating atmosphere;
5, slow down the preheating process of soft before melting.
Compared with the above, the pore in BGA assembly is formed with a slightly different pattern.
In general, the higher the solder bumps to porous BGA assembly mainly generated in board level assembly stage, in printed circuit board pre tinned, pore volume of BGA connector with the volatile solvent, elevated metal skin and soft melting temperature increasing, and decreases with the decrease of particle size. This can be determined by the flux increases; discharging speed of viscosity to be interpreted according to the model, in the soft melting temperature ribbed flux medium high viscosity may prevent the discharged from molten solder flux, therefore, to increase the likelihood of entrainment flux will increase the number of deflation, which leads to a larger porosity in the BGA assembly. Without considering the metallized area fixed solderability conditions, effects of solder reflow atmosphere on the activity and pore formation seems to be negligible, large void ratio will increase with the increase of the total pore volume, which shows that, compared with the total pore volume analysis results are shown, in BGA induced pore formation factors have greater influence on the reliability of welded joint, similar to this point and pore in SMT process generation condition.
Kai said
Solder reflow soldering is the main board level interconnect method for SMT assembly process, including the major problems affecting the reflow: bottom element is fixed, not weld fully, intermittent wetting, low residue, clearance, solder ball, solder beading, weld fillet weld is raised, TombstoningBGA ball bad, forming pore etc. that is not the only problem with this, not to mention the problem in this paper and leaching, intermetallic compound, non wetting, skew, lead-free welding, only by solving these problems, reflow soldering is an important SMT assembling method, in order to successfully preserved in ultra fine pitch period.
Causes and Countermeasures of solder bead
Han Xizhu phenomenon is the main defect of surface mount (SMT) process, mainly containing components in the chip resistor (CHIP) around, due to many reasons. Here through the analysis of the various possible causes of Han Xizhu, put forward the corresponding solution.
May be the reason for the following points:
Han Xizhu phenomenon is attached to the surface of one of the main defects of loading process, it is a complex process, which is the most annoying problem, to completely eliminate it, is very difficult.
Han Xizhu's diameter is approximately between 0.2mm~0.4mm, there are more than this range, mainly concentrated around the capacitance in chip resistor solder beads. There, not only affects the appearance of electronic products, but also the quality of the products the hidden trouble. The reason is the modern printed circuit element density is high, small spacing, solder ball may fall off when in use, thereby causing element short circuit, affecting the quality of electronic products. Therefore, it is necessary to understand its causes, and carry out effective control on it is particularly important.
In general, causes Han Xizhu is multifaceted, comprehensive, printing plate thickness solder paste, solder paste composition and the degree of oxidation, template making opening, solder paste is sucking up moisture, component mounting pressure, components and solder weldability, set the reflow temperature, the influence of the external environment it may be the cause of solder ball production.
Below, we reason from various aspects to solder bead and solution methods.
1, the solder paste selection directly affects the welding quality. The content of metal in the solder paste, solder paste oxidation degree of gold solder powder paste in size and solder paste printing to a printed board thickness can affect weld bead formation.
A, solder paste metal content. The metal content in the paste mass ratio 88%~92%, volume ratio is 50%, when the metal content increased, increasing the viscosity of the solder paste, it may resist vaporization preheating process to produce the force, in addition, the metal content increased, the metal powder arranged closely, the melting more let binding without being blown. In addition, an increase of the metal content may also reduce the solder paste printing after the "collapse", therefore, is not easy to produce solder beads.
B, solder paste metal oxidation degree. In the solder paste, the higher the degree of oxidation of the metal in the weld metal powder combined with resistance is greater, solder and pad between the components and the less infiltration, resulting in decreased solderability. Experiments show that the oxidation rate and the metal powder is directly proportional to the degree of general Han Xizhu., solder paste solder oxidation degree should be controlled below 0.05%, maximum limit is 0.15%.
C, particle size of metal powder paste. In the solder paste powder particle size smaller, solder paste surface area is larger, which leads to a fine powder oxidation degree is higher, so the phenomenon of increased solder beads. Our results showed that the solder paste is fine-grained, more prone to solder beads.
D, solder paste on a printed circuit board printing solder paste printing thickness. The thickness is an important parameter of bushing printing, usually between 0.12mm~0.20mm.
Solder paste is too thick will lead to paste "collapse", prompting Han Xizhu to produce.
E, and the amount of solder flux activity.
The flux was too much, the local will cause solder paste slump, so that the solder ball is easy to produce, in addition, active hours of flux, the flux of the oxygen ability is weak, which is also easy to produce solder ball.
No clean solder paste activity compared with rosin and water-soluble solder paste should be low, so it is more likely to have solder bead.
F, in addition, solder paste when in use, the general chilled in the refrigerator, take out after should make it back to room temperature after the open, otherwise, the solder paste to absorb water easily, in reflow solder beads splash.
2, mold production and opening.
We generally according to printing pad plate to create the template, so the apertures is pad size.
In the printing paste, easy to solder paste printing to solder house, resulting in a reflow solder beads produced.
Therefore, we can make template, the template openings than the actual size pad is reduced by 10%, in addition, can change the opening shape to achieve the ideal effect.
The template thickness determines the thickness of solder paste printing, so reducing the stencil thickness can also significantly improve the Han Xizhu phenomenon.
We have performed experiments: first to use 0.18mm thick template, after reflow solder side found blocking element bead is more serious, then, to make a template, the thickness is 0.
15mm, open form as a design before the map above, basically eliminated in reflow solder ball.
Parts mounting pressure and components of the solderability: if the pressure in the mount is too high, the solder paste is easy to grazing pressure to the solder layer element below, in the reflow soldering tin melting to the element is formed around the solder ball.
To solve the method can reduce the mount of pressure, and the above recommended template openings form to avoid solder paste is extruded to pad out.
In addition, components and solder pads also has a direct impact, if the oxidation of element and the pad is serious, will cause Han Xizhu.
After the pad hot air leveling in solder paste printing, the solder and flux change ratio, the flux ratio decreased, the pad is smaller, the imbalance is more serious, which is one reason why the Han Xizhu.
The reflow temperature settings: Han Xizhu is produced in the printed circuit board by reflow soldering, reflow soldering can be divided into four stages: pre heating, insulation, cooling and flow.
During the preheating stage makes the welding and element and pad temperature rises to between 120 to 150 degrees Celsius, reduced component thermal shock and streams, at this stage, the temperature rise can not be too fast, the general should be less than 105 degrees /s, too easy to cause the solder splash, formation of solder ball.
So we should adjust the reflow temperature curve, the preheating speed is moderate to control solder beads.
External factors: the best temperature of solder paste printing of 25+3 degrees Celsius, humidity 60% temperature relative humidity is too high, the solder paste easily absorbed moisture, prone to splash, this is the cause of solder beads.
In addition, PCB exposure in the air longer will absorb the moisture, and pad oxidation, solderability becomes poor, can be in the drying oven baked to remove moisture.
Thus, Han Xizhu formation is a complex process, we should consider in the tuning log, and explore the experience in production, the optimal control to welding solder balls.
The reasons and Countermeasures of bad welding patch
Tin bad
The surface of the phenomenon as the line some did not touch the tin, the reasons for:
1, coated with grease, and other impurities, can dissolve clean.
2, substrate manufacturing process grinding particles left on the surface line, this is the printed circuit board manufacturer problems.
3, silicone oil, general release agents and lubricants containing the oil, is not easy to clean, so in the production process of electronic parts, should try to avoid those chemicals containing silicone oil.
Oxidation of solder furnace to prevent oil also must pay attention to this kind of oil is not.
4, due to long storage time, the environment or the process properly, the substrate or parts of the tin surface oxide and copper surface and in severe cases.
Using flux often fail to solve this problem, a heavy welding will be helpful to the soldering effect.
5, the use of improper adjustment of flux condition, such as blowing air pressure required height.
Specific gravity is also one of the important factors, because the line surface flux distribution quantity by gravity effect.
Check the proportion can be excluded for label wrong, storage conditions and poor causes improper possibility misuse of flux.
6, soldering temperature and time is not enough.
General soldering operation temperature is the melting temperature 55~88 degrees Celsius higher.
Part 7, terminal material, not suitable for the inspection of parts, the terminal cleaning, dip good.
8, the preheating temperature is not enough, can adjust the preheating temperature, the substrate part side surface temperature temperature reach the requirement of about 90 to 110 degrees celsius.
9, too many acrobatic component solder, does not meet the requirements.
Can time measurement in solder, acrobatics, if not more than the standard provisions, replace the solder in the standard.
Tin
Occurred in the lead tin tin tin, similar adverse circumstances; but in Xi road surface people tin to welding wave detachment, solder has been largely stick on and pulled back to the stove, so the situation is serious tin bad, heavy welding time does not necessarily improve.
The reason is the substrate manufacturing plant in Du tin lead before wash the face clean the substrate can be sent to the factory to handle bad.
Cold solder or solder joint is not smooth
This situation can be classified as a solder joint uneven, occurred in the substrate from the wave is solidified, the solder joint parts under external influence movement formed.
Keep the substrate in the transfer action solder after the smooth, such as strengthening the parts of the fixed, pay attention to parts molding direction; in short, the substrate to be welded over sufficiently cooled to move, can avoid this problem.
The solution to a tin wave.
As for cold welding, solder temperature is too high or too low may have caused this situation.
The solder joint crack
The reasons for the substrate, through parts of foot hole and the solder joint during thermal expansion coefficient mismatch, is actually not solder issue, but involves wiring and parts design, coordination, material and size in the heat. In addition, the collision substrate assembly, one of the main folding is. The reason therefore, substrate assembly is not collision, would have to be stacked, accumulation.
Also, by cutting machine cutting molding is the main killer, countermeasure using automatic plug-in machine or prior shear pin or purchase does not have to cut the foot parts.
Tin too much
The solder joint is too large is not on the current circulation to help, but on the strength of the solder joint is not affected, the reasons are:
1 degree properly, change the angle (10~70), can dissolve tin from line drop with a large force, and solder joint thinner.
2, low degree or soldering time is too short, to dissolve tin surface line is not completely drop condensed.
3, is not enough, so that the flux is not fully play the role of clean surface.
4, the flux ratio, will also help to avoid the big spot occurrence; however, must also pay attention to the proportion is too high, after the substrate solder flux residue residue you.
Tin tip
Step end to form along the line parts, solder another shape too much.
Again the tip to eliminate solder.
Sometimes it is also bad not eat and eat tin and tin occur at the same time, the reasons are as follows:
,
1, the substrate weldability is poor, the inference from the line contact edge of tin and tin to confirm the poor do not eat.
In this case, again through tin stove does not solve the problem, because, as mentioned before, the line surface situation is not good, so processing method will be invalid.
2, macroporous substrate without plugins.
Solder into the hole, when condensation soldering holes in because the number is too much, be gravity pulled into icicles.
3, in the hand soldering, is the main reason for not tip temperature, or although the temperature is enough, but the iron head on the solder too much, also can have the effect.
4, impurity content of metal is high, need to add or replace pure tin solder.
Solder attached to the substrate material.
1, if the chemical flux formulation is not compatible with the residues in the substrate, will cause the case.
In welding, this material for high-temperature soft, sticky, and with some paste.
Use of such chemicals strong solvents such as ketones, cleaning the substrate, will help to send.
If it still happens flux is attached to the substrate, may be the substrate during the baking process handling.
2, substrate manufacturing factory in laminated plate drying process properly, placed in the box with 80 to 100 degrees bake for 2 to 3 hours in the substrate assembly before, or can improve this problem.
3, the oxide and substrate contact in solder, acrobatics have caused this phenomenon, this is the problem of equipment maintenance.
White residue
Solder after cleaning, sometimes found a white residue substrate, although does not affect the surface resistance value, but because of the appearance of the factors still unacceptable.
The reasons for:
1, the substrate itself has a residue, absorbed flux, followed by soldering and cleaning on the formation of white residue, keep the substrate before welding
No residue is very important.
2, dry laminate properly, occasionally found a batch of substrates, there is always the soul residue problem, and the use of a batch of substrates, and disappear automatically. Because of this reason, resulting in white residue can generally clean using solvent.
3, copper surface oxidation inhibitor formulations are not compatible. Must have a copper surface oxidation preventing agent in copper panel, smear the substrate manufacturing factory. The copper oxide to prevent are rosin as the main raw material, but the use of water soluble flux in the soldering process. So in the assembly line wash supernatant substrate after showing a rosin residue soul. If the cleaning process with a halogenating agent can this problem. Currently existing water solvent copper surface oxidation inhibitor.
4, substrate manufacturing processes improper control of the substrate modification.
5, the use of the old welding course, absorb the moisture in the air, white residue water formed in the solder process.
6, the substrate in the use of rosin flux, solder after the time stay too and before cleaning, cleaning is not easy to attain, as far as possible to shorten the delay time between soldering and cleaning, will send this phenomenon.
7, excessive cleaning substrate moisture content in solvent, absorption of IPA ingredients locally stored in solvent, reduce the cleaning ability. Solutions to the appropriate solvent removal of moisture, such as the use of water separator or the water absorbing material in the separator medium.
Dark residues expanding erosion trace
In the base line and solder joint surface, double plate on both sides are likely to change this situation, usually because the use of flux and improper cleaning.
1, in the use of rosin flux, solder is not in a short period of time. Time delay too long cleaning cleaning, resulting in the substrate remaining traces.
2, the residual acid flux also will cause solder dark and traces of corrosion. The solution for cleaning immediately in the solder, or in the cleaning process, adding neutralizing agent.
3, because the flux residue soldering temperature is too high and the blackened, suggested solutions to detect flux factory solder temperature. The use of flux may allow higher temperature can avoid the occurrence of this situation.
4, solder impurity content does not meet the requirements, need to add or replace pure tin solder.
Pinhole or porosity
On the surface, the pinhole and porosity in different pinhole diameter smaller, now on the surface, can see the bottom. The pinhole and stomatal represents a bubble solder joints, but has not been extended to the surface, most of them in the bottom of the bottom substrate, when the bubble burst before the complete diffusion condensation, i.e. pinhole or the following reasons for the formation of pores:
1, with the organic pollutants in the molding substrate or parts. This kind of pollution material from automatic plug-in machines, machine parts and storage of adverse factors. In ordinary solvents can easily remove the pollutants, but encountered silicone oil and similar silicon containing products is difficult. If the problem is caused by silicone oil is required because. Consider the source change lubrication or release agent.
2, the substrate containing plating solution and similar materials produced water, if the substrate using cheaper materials, there may be inhaled the vapors solder produce enough heat to cause porosity by solution gasification. Before assembly, the substrate of the baking in the oven, can improve this problem.
3, substrate storage too much or because of improper, absorption near ambient moisture, so the assembly before baking.
4, the flux tank containing water, need to replace the flux regularly.
5, and air knife compression contains too much moisture in the air, need to install a water purifier, and regular exhaust.
6, the preheating temperature is too low, no steam or solvent, substrate is once in the tin furnace, instant contact with high temperature, and produce burst, so higher preheating temperature.
7, 锡温 too high, in water or solvent, immediately burst, so need to lower the soldering temperature.
Short circuit
1, the pad design properly, can be composed of a circular pad to elliptic, increasing the distance between points.
The 2 part direction, improper design, such as SOIC if the foot and the tin wave parallel, for short, modified parts of the vertical direction and wave.
3, automatic plug-in clubfoot caused due to IPC regulations. In the 2mm length (short of danger) and worry clubfoot angle is too large parts will drop, so it is easy to therefore caused by short circuit, the spot left line of more than 2mm.
4, the substrate hole, side hole penetrates the tin by substrate caused by short circuit, so it needs to be reduced to does not affect the part inserted degree aperture.
5, automatic plug-in, the remaining parts of the foot is too long, need to limit below 2mm.
6, tin furnace temperature is too low, tin not quickly drop back, need to adjust the high tin furnace temperature.
7, the conveyor speed is too slow, not rapid drop back, tin, need to adjust quickly the speed of the conveyor belt.
8, the plate weldability is poor, will be clean.
9, the glass material overflow substrate, before welding inspection panel if there is a glass protrusion.
10, the solder mask failure, check the appropriate solder mask and use method.
11, surface pollution, will be clean.
Contact the dark and granular
1, much due to the solder by pollution and excessive mixed oxides dissolve tin, solder joint formation structure is too brittle. Should pay attention not to people using solder low tin ingredients containing causing dark confusion.
2, the solder itself composition changes, acrobatic content too much, need to add or replace pure tin solder.
Mark
Glass fiber layer of physical changes, such as separation phenomenon between layer and layer. But this is not the case. The reason is the solder substrate heating, high need to reduce preheat and soldering temperature or increasing the substrate speed.
The solder joint is golden yellow
The solder temperature is too high, to lower the soldering temperature
Welding rough
1, the improper time - temperature relationship, can weld preheating temperature in order to establish the proper relationship of correction in the conveyor belt speed
2, the solder composition is not correct, check the solder composition, to determine the type of alloy solder and appropriate welding temperature.
3, the solder cooled antecedents of mechanical vibration caused by, check the conveyor belt, to ensure that the substrate in welding and solidification, without collision or shaking.
4, the solder is polluted. Check the impurity pollution caused by type and determine the appropriate methods to reduce or eliminate the pollution of soldering tin bath (diluted or replaced solder)
Welding and welding projecting into pieces
1, the conveyor speed too fast, slow down the speed of the conveyor belt.
2, the welding temperature is too low, higher tin furnace temperature.
3, the two welding waveform is low, re adjust the two welding waveform.
4, the waveform is inappropriate or waveform and face angle and improper output waveform is improper. Can be re adjusted waveform and belt angle.
5, the surface pollution and weldability is poor, shall improve clean its weldability.
The solder substrate surface too much
1, tin or too high a level is too high, so that over the substrate, tin or tin wave height.
2, the substrate holder would not appropriate, induced the tin surface over the substrate surface, design or modify the substrate fixture.
3, size appropriate wire and the substrate hole. Redesign substrate hole the size, replacement parts when necessary.
Substrate deformation
1, the fixture is not suitable, the substrate deformation, resetting fixture.
2, the heat temperature is too high, reduce the preheat temperature.
3, tin temperature is too high, reduce the 锡温.
4, the conveyor speed is too slow, resulting in the surface of the substrate temperature is too high, increase the speed of the conveyor belt.
5, after the substrate of each parts arranged weight distribution is not average, but the improper design, re design surface, eliminate the heat concentrated in one area, and the weight is concentrated in one area, and weight concentrated in the center.
6, substrate storage or process occurs in stacking pressure caused by deformation.
Conclusion
All solder defects, in addition to spots and white residue, will influence the electrical properties or functions, even the whole line faults. Early in the production process to find out why parallel local treatment, in order to reduce and avoid costly repairs, through appropriate substrate design and process control of good will can be reduced. The disadvantages and achieve zero goals.
The use of high-quality selection of solder, flux suitable for application, notice and improve the possibility of parts, soldering process of the variable control properly, will ensure a high quality soldering effect.
Production of solder paste
A mature paste formulation to have what thing
Answer: a proven formula, this meaning may be more difficult to decide, generally refers to the formulation of production of solder paste in the market has been mature sales as a benchmark, but the process, country environment, sheet metal, machine, machine, artificial, influence of parameter setting and other factors, is the international brand of solder paste is also different in the effect of different manufacturers.
If only from the theoretical sense, the so-called mature solder paste formulations should be used once qualified rate of 80--90 can be achieved in different manufacturers, but also needs to have the ingredients list reasonable, transparent material name and number, the ratio of raw materials and detailed add the correct order, operating environment requirements.
Within the production process, factors of the manual operation influence on the solder paste quality is not very important, or as long as there are recipes, anyone can do it -
Answer: in the solder paste production process, factors of human influence on the solder paste quality is important, not as long as the formula, anyone can do hold the specific requirements of solder paste production, earnestly implement and in the actual production process. In addition, it should be to learn the performance and characteristics every kind of material added solder paste, generally need to have chemical technician responsible for such work
The experiments and production gap in what aspects.
Answer: the experiment has the following with series gap:
1, the process is simple, relatively small amount, revealing too much problem is not;
2, in the production process is easy to see the actual production in the proportion of different;
3, the actual production, because the whole process time than the experimental time is long, is not the same as the control method of long time tin or soldering paste quality;
4, the production process, there will be batch quality between the inconsistent condition, which depends on the raw materials and production process, and has not these problems in experiment
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