Countermeasures of wave soldering

Insufficient solder

Causes and preventive measures PCB preheating and welding temperature are too high, which makes the viscosity of molten solder too low. The preheating temperature is 90- 130℃, and the upper limit is taken when there are many mounted components; The temperature of tin wave is 250 5℃, and the welding time is 3-5s.

The aperture of the insertion hole is too large, and the solder flows out of the hole. The aperture ratio needle diameter of the jack is 0. 15-0.4mm (the lower limit of fine needle and the upper limit of thick needle).

Thin leads and large pads, solder is pulled onto the pads to dry the solder joints. The pad design should meet the requirements of wave soldering.

The quality of metallized holes is poor or flux flows into the holes. Reflect it to PCB processing factory to improve the processing quality.

The peak height is not enough. Printed boards cannot exert pressure on solder, which is not conducive to tin plating. The peak height is generally controlled at 2/3 of the PCB thickness.

The inclination angle of PCB is too small, which is not conducive to flux discharge. The climbing angle of the printed board is 3-7 degrees.

Too much solder

The viscosity of the molten solder is too high because the welding temperature is too low or the speed of the conveyor belt is too fast. The temperature of tin wave is 250 5℃, and the welding time is 3-5s.

According to the PCB size, whether there are multilayer boards, the number of components and whether there are mounted components, the preheating temperature is set.

Flux activity is poor or its specific gravity is too small. Replace the flux or adjust the proper specific gravity.

The solderability of pads, sockets and pins is poor. In order to improve the processing quality of printed circuit boards, components should be used on a first-come-first-served basis and should not be stored in a humid environment.

The proportion of tin in solder decreases, or the impurity composition in solder is too high (Cu

There is too much solder residue. Clean up the residue after work every day.

Tin wire

The preheating temperature of PCB is too low, because the temperature of PCB and components is too low, and the overflowing solder sticks to the surface of PCB when contacting with the wave crest. Increase preheating temperature or prolong preheating time.

Printed boards are wet. Dehumidify the printed circuit board.

The solder mask is rough and uneven in thickness. Improve the processing quality of printed boards.

Missing welding (virtual welding)

Explanation of terms: Generally, Cu-Sn alloy layer with appropriate thickness will not be formed at the joint boundary during brazing.

Reasons for missing welding (virtual welding):

1. Low brazing temperature and insufficient heating. Low temperature of solder bath-too fast clamping speed-poor design.

2.2 Solderability. Bad PCB or component lead. Oxidation pollution of base metal-too high welding temperature-too low welding temperature-too long welding time.

3. Solder will vibrate before solidification.

4. Flux inflow.

Solution of missing welding (virtual welding);

1. Clean all welding surfaces before welding. Ensure weldability.

2. Adjust the welding temperature.

3. Enhance the activity of flux.

4. Reasonable selection of welding time.

5. Improve the storage conditions and shorten the storage time of PCB and components.

cold welding

Explanation of cold welding terms: After wave welding, irregular fillet weld appears in the solder joint, and there is no wetting or insufficient wetting between the solders in the base metal box, or even cracks appear.

Due to the vibration of the conveyor belt, the solder is disordered due to the influence of external force during cooling. Check whether the motor is faulty and the voltage is stable. Whether there are foreign objects on the conveyor belt.

The viscosity of the molten solder is too high because the welding temperature is too low or the speed of the conveyor belt is too fast. Wrinkle the surface of solder joint. The temperature of tin wave is 250 5℃, and the welding time is 3-5s. When the temperature is slightly lower, the speed of the conveyor belt should be slowed down.

Reasons for cold welding:

1. The temperature of the solder pool is very low.

2. The clamping speed is too high and the welding time is short.

3. During the normal welding of 3. PCB, due to the solder joints of components with large heat capacity, has insufficient heat accumulation.

Cold welding solution:

1. Increase the temperature of the solder bath.

2. Reduce the clamping speed and control the welding time in 3-5s.

3. When the preheating zone reaches the solder pool, increase the preheating temperature to reduce the thermal shock of PCB.

Welding point diagram

The height of the peak of the electromagnetic pump wave soldering machine is too high or the pin is too long, which makes the bottom of the pin unable to contact with the peak. Because the electromagnetic pump wave soldering machine is hollow wave, the thickness of hollow wave is about 4-5 mm, and the peak height is generally controlled at 2/3 of the thickness of PCB. The pin formation of plug-in components requires that the original pin be exposed from the welding surface of printed board by 0.8-3 mm

Flux has poor activity. Replace the flux.

The ratio of the lead diameter of the plug-in to the hole diameter of the plug-in hole is incorrect, the plug-in hole is too large, and the large pad absorbs heat. The aperture ratio needle diameter of the jack is 0. 15-0.4mm (the lower limit of fine needle and the upper limit of thick needle).

Tapping characteristics:

The drawing points have metallic luster and are thin and pointed.

The temperature of the solder bath is low and the clamping speed is too fast.

When the painting tip has a round, short, thick and five-light state.

Solder has high temperature and high speed.

Reasons for the formation of the tip:

1. The liner is oxidized.

2. The amount of flux is very small.

3. Improper preheating.

4. The temperature of the solder pool is very low.

5. The clamping speed and welding time are too long.

6.PCB pressure wave depth is too large.

7. The copper foil is too big and the PCB is too small.

8. The flux is unsuitable or deteriorated.

9. The purity of solder is not suitable.

10. Uncomfortable angle.

Tapping solutions:

1. Clean the welding surface.

2. Increase flux spray.

3. Adjust the preheating temperature properly. 120- 135

4. Adjust the temperature of the tin furnace properly. 268-275

5. Speed up the clamping speed and reduce the welding time. 1.0 1.5m/ min

6. Adjust the peak height.

7. Change the PCB pad design.

8. Replace the flux.

9. Replace the solder.

10. Change the clamping angle.

cavity

Reasons for the formation of cavities:

The matching relationship between 1. hole and wire is seriously unbalanced, and almost 100% of the small wave soldering of large hole leads has cavity phenomenon.

2.PCB perforation deviates from the pad center.

3. The pad is incomplete.

4. There is burr or oxidation around the hole.

5. Lead wire is oxidized and dirty, and the pretreatment is not good.

Empty solution:

1. Adjust the hole line fit.

2. Improve the processing accuracy and quality of pad holes.

3. Improve the processing quality of PCB.

4. Improve the cleanliness and solderability of the surface of the bonding pad and lead.

Solder ball (bead)

The preheating temperature of PCB is too low or the preheating time is too short, and the solvent and moisture in flux are not volatilized, which leads to solder splashing during welding. Increase preheating temperature or prolong preheating time.

Reasons for spattering of solder balls (beads):

1.PCB gets wet during manufacturing or storage.

2. The ambient humidity is high, and the moisture condenses on the multi-seam PCB, and no moisture inspection measures are taken in the factory building.

3. The coating and flux are immiscible, and the flux is improperly selected.

4. If the flux is missing or the coating amount is out of range, the flux absorbs water and intercepts it.

5. The solder resist layer is poor and solder residue is attached.

6. Bad substrate treatment and rough hole wall lead to the accumulation of bath liquid, which was not analyzed during PCB design.

7. The preheating temperature is not suitable.

8. The silver-plated part is dense.

9. The choice of solder wave crest shape is not appropriate.

Splash tin ball (bead) solution;

1. Change PCB storage conditions to reduce moisture.

2. Choose the appropriate flux.

3. Spray flux evenly to increase preheating temperature.

4. Change the PCB design scheme and analyze the thermal uniformity.

5. Kaiping wave PCB solder joint.

Air holes (bubbles/pinholes)

Too many impurities and too high AL content in the solder will make the solder joint hollow. Replace the solder.

Oxides and residues on the surface of solder are seriously polluted. Clean up the residue after work every day.

The inclination angle of PCB is too small, which is not conducive to flux discharge. The climbing angle of the printed board is 3-7 degrees.

The peak height is too low, which is not conducive to exhaust. The peak height is generally controlled at 2/3 of the PCB thickness.

Causes of air holes (bubbles or pinholes):

1. Too much flux or insufficient quantity before welding.

2. The substrate is wet.

3. The position of the hole and the size of the lead gap, as well as whether the exhaust of the substrate is smooth.

4. Bad porous metal.

In the process of wave soldering, the heat capacity of the heated substrate is very large. Although the welding has ended, it has not cooled down. Due to thermal inertia, the temperature still rises. At this time, the outside of the solder joint began to solidify, while the temperature inside the solder joint slowly decreased. The residual gas continues to expand, squeezing the solder that is about to solidify on the outer surface and spraying it, thus forming holes at the solder joints.

Pore (bubble or pinhole) solution:

1. Improve preheating temperature and give full play to the role of flux.

2. Shorten the pre-storage time of the substrate.

3. Properly design the gasket to ensure smooth exhaust.

4. Prevent oxidation pollution of pad metal.

Poor wettability:

The poor adhesion of metal electrode at the end of chip module or the use of single-layer electrode lead to the phenomenon of cap removal at welding temperature. Wave soldering of surface mount components adopts three-layer tip structure, which can withstand more than two wave soldering temperature shocks at 260℃.

PCB design is unreasonable, and shadowing effect leads to missing soldering during wave soldering. Meet DFM design requirements

PCB warpage leads to poor contact between PCB warpage position and wave crest. The warpage of printed circuit board is less than 0.8- 1.0%.

The two sides of the conveyor belt are not parallel, which leads to the non-parallel contact between PCB and wave crest. Adjust the level.

The peak is uneven, and the heights on both sides of the peak are not parallel. Especially, if the tin wave nozzle of electromagnetic pump wave soldering machine is blocked by oxide, the wave crest will appear sawtooth, which is easy to cause missing welding and virtual welding. Clean the tin wave nozzle.

Poor flux activity will lead to poor wettability. Replace the flux. The preheating temperature of PCB is too high, which makes the flux carbonized and inactive, resulting in poor wetting. Set an appropriate preheating temperature.

Non-wetting and reverse wetting

Non-wetting: after wave soldering, a continuous solder film is produced on the surface of the base metal. On the non-wetting surface, the solder does not contact the base metal at all, but cotton thread can be seen on the exposed base metal surface.

Wet-back: The solder of wave soldering first wets the surface of the base metal, and then retracts due to insufficient wetting, thus leaving a layer of wave soldering material on the surface of the base metal, and at the same time, there are intermittent and somewhat separated solder balls, and the contact angle of the big solder ball at the contact position of the base metal is very large.

Reverse wetting is similar to some form of pollution on the surface of non-wetting base metal, which will produce semi-wetting phenomenon.

When the concentration of metal impurities in the solder bath reaches a certain value, semi-wetting will also occur.

Reasons for non-wetting and rewetting:

1. The basic metal body cannot be welded.

2. Flux activity is insufficient or deteriorated.

3. Oil or grease on the surface will prevent flux and solder from contacting the welding surface.

4. Improper control of wave soldering time or temperature.

Non-wetting and Back-wetting Solutions:

1. Improve the weldability of welding metal.

2. Switch to effective flux.

3. Adjust the temperature and time of flux reasonably.

4. Thoroughly remove the pollutants on the welding metal surface.

5. Keep the purity of the solder in the solder bath.

Contour structure of solder joint (surface treatment/drying)

Causes of conformal formation of solder joint profile;

Over-docking of solder leads to excessive accumulation of solder on the solder joint to form a convex shape, and the outline of the component pin line cannot be seen.

The solder is too little and dry, and there is a serious lack of seats, so it is impossible to completely seal the connected wires and expose a part.

If the contact angle is 0; The tensile strength of 45 is also large, and the average tensile strength is also lower than the maximum.

The optimal contact angle range is 65438+05.

It is required to extend the wetting height H≥D of solder joints of leads as shown in Figure 3.

Contour conformal solution of solder joint;

1. Improve the weldability of the surface state of the welded metal.

2. Tangent graphics and wiring of actual PCB.

3. Adjust the solder temperature, clamping speed and clamping angle reasonably.

4. Adjust the preheating temperature reasonably.

Dark solder joints or granular solder joints

Causes of formation of dark solder joint or particle solder joint:

1. Excessive accumulation of metal essence in solder makes the solder joint dark gray or white.

2. The amount of metal in the solder is reduced.

3. Chemical corrosion darkens the solder joint.

4. Anti-oxidation oil will make the solder joint produce particles and unevenness.

5. Overheating during welding.

Solutions for dark solder joints or granular solder joints;

1. Replace the tin bath.

2. Purify other impurities in the tin furnace with pure tin.

3. Reduce the welding temperature.

Solder joint bridging or short circuit

Explanation of solder joint bridging or short circuit: Too much solder makes adjacent lines or pile up on the same conductor, which are called bridging and short circuit respectively.

The PCB design is unreasonable and the pad spacing is too narrow. Meet DFM design requirements.

The pins of the plug-in are irregular or skewed, and the pins are close or touching before welding. The pins of the plug-in should be shaped according to the aperture and assembly requirements of the printed board. If the short plug-in welding process is adopted, the original pin should be exposed from the welding surface of the printed board by 0.8-3mm, and the element should be straight when inserted.

The viscosity of the molten solder is too high because the contact temperature is too low or the speed of the conveyor belt is too fast. The temperature of tin wave is 250 5℃, and the welding time is 3-5s. When the temperature is slightly lower, the speed of the conveyor belt should be slowed down.

Flux has poor activity. Replace the flux.

Causes of bridging and short circuit:

1. temperature

2. The distance between adjacent bonding wires or pads is too short.

3. The surface of the base metal is not clean.

4. The purity of solder is not enough.

5. Flux activity and preheating temperature.

Design of 6.6. The PCB electrical equipment is unreasonable, and the heat capacity of the board surface is too large.

7.PCB eats tin depth.

8. Height of component pin protruding from PCB

9.PCB clamping speed.

10.PCB included angle.