Common Defects and Solutions in Dispensing Process>>>>

Wire drawing/Trailing

 

1.1.1, wire drawing/Sagging is a common defect in dispensing,The common causes are that the inner diameter of the glue nozzle is too small, the dispensing pressure is too high, and the glue nozzle is away from the PCB.The spacing is too large, the patch glue expires or the quality is not good, the viscosity of the patch glue is too good, it fails to return to room temperature after being taken out of the refrigerator, the amount of glue is too large, etc.

1.1.2Solution:Replace the rubber nozzle with larger inner diameter;Reduce the dispensing pressure;Adjust the height of the "stop;Change the glue and select the appropriate viscosity of the glue. After the patch glue is taken out of the refrigerator, it should be returned to room temperature (about 4h) and then put into production. Adjust the dispensing amount.

 

 

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Glue nozzle blocked

 

1.2.1The fault phenomenon is that the amount of glue from the glue nozzle is too small or there is no glue point.The reason is that the pinhole is generally not completely cleaned;Impurities are mixed in the patch glue,Plugging;A mixture of insoluble glues.

1.2.2Solution:Replace the clean needle;Change the good quality patch glue;The label of the patch should not be mistaken.

 

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1.3.1The phenomenon is only dispensing action,But there is no glue.The reason is that the patch glue is mixed with bubbles;The glue nozzle is blocked.

1.3.2Solution:The glue in the syringe should be debubbled (especially self-installed glue);Replace the rubber nozzle.

 

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Component shift

 

1.4.1The phenomenon is the displacement of components after the adhesive is cured,In severe cases, the component pins are not on the pad.The reason is that the amount of adhesive is uneven,For example, one more and one less in the two-point glue of the chip component;The component shifts during the patch or the initial adhesion of the patch adhesive is low; The PCB is placed for too long after dispensing. The glue is semi-cured.

1.4.2Solution:Check whether the glue nozzle is blocked,Eliminate uneven glue;Adjust the working state of placement machine;Change glue; PCB placement time should not be too long after dispensing (shorter than 4h)

 

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The film will fall off after wave soldering.

 

1.5.1The phenomenon is that the bonding strength of the components after curing is not enough,below the specified value,Sometimes the film will fall off when touched by hand.The reason is that the curing process parameters are not in place,In particular, the temperature is not enough, the component size is too large, and the heat absorption is large; the curing lamp is aging; the amount of glue is not enough; the component/PCB is polluted.

1.5.2Solution:Adjust the cure curve,in particular, increasing the curing temperature,Usually the peak curing temperature of hot curing adhesive is 150C, less than the peak temperature is likely to cause the film to fall off. For light-curing glue, it should be observed whether the light curing lamp is aging and whether the lamp tube is black. The quantity of glue and whether there is pollution in the component/PCB are all issues that should be considered.

 

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Component pin floating after curing/Shift

 

1.6.1The phenomenon of this failure is that the component pins float or shift after curing,After wave soldering, tin material will enter under the pad,In severe cases, short circuits and open circuits may occur.The main causes are uneven patch glue, excessive amount of patch glue or component offset during patch.

1.6.2Solution:Adjust the dispensing process parameters;Control the dispensing volume;Adjust the patch process parameters.

 

Quality Analysis of Solder Paste Printing and Patch

Analysis of Solder Paste Printing Quality

The quality problems caused by poor solder paste printing are the following:

①Insufficient solder paste (Local lack or even overall lack) will lead to insufficient solder quantity of components after welding, open circuit of components, deviation of components and erection of components.

②Solder paste adhesion will lead to short circuit and component deviation after soldering.

③The overall deviation of solder paste printing will lead to poor welding of the whole board components,Such as less tin, open circuit, deviation, vertical pieces, etc.

④Solder paste tip pulling can easily cause short circuit after welding.

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The main factors leading to insufficient solder paste

 

1.1When the printing press is working,There is no timely supplement to add solder paste.

1.21. The quality of solder paste is abnormal,It's mixed with hard lumps and other foreign matter.

1.3The previously unused solder paste has expired,To be used twice.

1.4circuit board quality problems,There's an inconspicuous covering over the pads,For example, solder resist printed on the pad (green oil).

1.5The fixed clamp of the circuit board in the printer is loose.

1.6The thickness of solder paste leakage screen is uneven.

1.7, solder paste leakage printing screen or circuit board has contaminants (such as PCBpackaging, wipes, foreign bodies floating in the ambient air, etc.).

1.82. The solder paste scraper is damaged, and the screen plate is damaged.

1.9The pressure, angle, speed and demoulding speed of the solder paste scraper are not properly set.

1.10After the solder paste printing is completed,It was accidentally knocked off because of human factors.

 

 

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The main factors leading to solder paste adhesion

 

2.1design defects of the circuit board,Pad spacing is too small.

2.2, screen problem,The position of the hole is not right.

2.3The screen is not wiped clean.

2.4The screen problem causes the solder paste to fall off poorly.

2.5Poor performance of solder paste,Viscosity and collapse are unqualified.

2.6The fixed clamp of the circuit board in the printer is loose.

2.7The pressure, angle, speed and demoulding speed of the solder paste scraper are not properly set.

2.8After the solder paste printing is completed,Because human factors are squeezed adhesion.

 

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The main factors leading to the overall deviation of solder paste printing

 

3.1The positioning reference point on the circuit board is not clear.

3.2The positioning reference point on the circuit board is not aligned with the reference point of the screen board.

3.3The fixed clamp of the circuit board in the printer is loose.Positioning thimble is not in place.

3.43. The optical positioning system of the printing press is faulty.

3.5The solder paste leakage screen opening does not conform to the design documents of the circuit board.

 

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The main factors leading to the printing of solder paste tip

 

4.1Solder paste viscosity and other performance parameters have problems.

4.2There is a problem with the demoulding parameter setting when the circuit board is separated from the printed screen,

4.3There are burrs on the hole wall of the screen hole.

 

patch quality analysis

 

SMTCommon quality problems of patches include missing parts, side parts, turning parts, deviation, damaged parts, etc.

 

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Main factors leading to patch leakage

 

1.12. Component FeederFeeding is not in place.

1.2The air path of the component suction nozzle is blocked, the suction nozzle is damaged, and the height of the suction nozzle is incorrect.

1.3Failure of vacuum gas circuit of equipment,A blockage has occurred.

1.4Poor circuit board purchase,produce deformation.

1.5There is no solder paste or too little solder paste on the pad of the circuit board.

1.6Quality problems of components,The thickness of the same variety is inconsistent.

1.7There are errors and omissions in the calling program of the mounter,Or the wrong choice of component thickness parameters during programming.

1.8, human factors accidentally touch off.

 

 

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Lead to SMCThe main factors of turning parts and side parts when the resistor is attached.

 

2.12. Component FeederAbnormal feeding.

2.22. The suction nozzle of the mounting head is at wrong height.

2.32. The height of the material grabbing by the mounting head is incorrect.

2.4The size of the loading hole of the component braid is too large,Component flipped over due to vibration.

2.5The bulk material is put into the braid in the opposite direction.

 

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Main factors leading to component patch deviation

 

3.1When the placement machine is programmed,X-Y of componentsAxis coordinates are incorrect.

3.2, patch suction nozzle reason,Make the suction material unstable.

 

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The main factors that lead to the damage of components when pasting

 

4.1Positioning thimble too high,The position of the circuit board is too high,Components are squeezed during placement.

4.2When the placement machine is programmed,Z of ComponentsAxis coordinates are incorrect.

4.3The nozzle spring of the mounting head is stuck.

 

Factors Affecting the Quality of Reflow Soldering>>>>

Influence Factors of Solder Paste

 

The quality of reflow soldering is affected by many factors,The most important factors are the temperature profile of the reflow furnace and the composition parameters of the solder paste.Now commonly used high-performance reflow furnace,It is easy to accurately control and adjust the temperature curve.In contrast, in the trend of high density and miniaturization, the printing of solder paste has become the key to the quality of reflow soldering.

The particle shape of solder paste alloy powder is related to the welding quality of narrow pitch devices,The viscosity and composition of the solder paste must also be selected appropriately.In addition,Solder paste general refrigerated storage,The cover can only be opened after it is returned to room temperature when it is taken. Special attention should be paid to avoid mixing the solder paste with water vapor due to temperature difference. When necessary, stir the solder paste with a blender.

 

 

 

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Effect of welding equipment

 

Sometimes,Excessive vibration of the conveyor belt of reflow welding equipment is also one of the factors affecting welding quality.

 

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Effect of reflow soldering process

 

In the exclusion of solder paste