Frequently Asked Questions about Wave Soldering: Causes and Solutions for Welding Defects

This article introduces you to the soldering problems encountered with Wave soldering and the corresponding soldering solutions.

Solder joints are dry/incomplete/cavity, the insertion holes and vias are not full of solder, and the solder does not climb onto the pads on the component side.

a) PCB preheating and soldering temperature are too high, so that the viscosity of the solder is too low;

b) the aperture of the insertion hole is too large, and the solder flows out of the hole;

c) inserting components with thin leads and large pads, the solder is pulled onto the pads to dry the solder joints;

d) the metallized hole is of poor quality or the solder resist flows into the hole;

e) PCB climbing angle is too small, which is not conducive to flux exhaust.

a) Preheating temperature is 90-130 °C, the upper limit is taken when there are many components, the tin wave temperature is 250 +/- 5 °C, and the welding time is 3~5S.

b) The aperture of the insertion hole is 0.15~0.4mm larger than the diameter of the lead, the lower lead is taken as the lower limit, and the thick lead is taken up.

c) The pad size and pin diameter should be matched to facilitate the formation of the meniscus;

d) reflected to the PCB processing plant to improve the processing quality;

e) The climbing angle of the PCB is 3 to 7 °C.

The solder tails and leads of the component are surrounded by excessive solder with a wetting angle greater than 90°.

a) the soldering temperature is too low or the belt speed is too fast, so that the viscosity of the molten solder is too large;

b) The preheating temperature of the PCB is too low, and the components and the PCB absorb heat during soldering, so that the actual soldering temperature is lowered;

c) the activity of the flux is poor or the specific gravity is too small;

d) The pads, the insertion holes or the pins are poorly solderable and cannot be fully wetted, and the generated bubbles are wrapped in the solder joints;

e) The proportion of tin in the solder is reduced, or the composition of the impurity Cu in the solder is high, which increases the viscosity of the solder and deteriorates the fluidity.

f) Too much solder residue.

a) Tin-wave temperature 250 +/- 5 ° C, welding time 3 ~ 5S.

b) According to the PCB size, the layer, the number of components, the presence or absence of mounting components, etc., the preheating temperature is set, and the bottom temperature of the PCB is 90-130.

c) replace the flux or adjust the appropriate ratio;

d) Improve the processing quality of the PCB board, the components should be used first-time, not stored in a humid environment;

e) When the proportion of tin is <61.4%, some pure tin may be added in an appropriate amount. When the impurity is too high, the solder should be replaced;

f) The residue should be cleaned up at the end of each day.

a) The PCB design is unreasonable and the pad pitch is too narrow;

b) the components of the plug-in components are irregular or the package is skewed, and the pins are close to or have been touched before soldering;

c) The preheating temperature of the PCB is too low, and the components and the PCB absorb heat during soldering, so that the actual soldering temperature is lowered;

d) the soldering temperature is too low or the belt speed is too fast, so that the viscosity of the molten solder is lowered;

e) Solder resist activity is poor.

a) Design according to PCB design specifications. The long axis of the two end Chip components should be as perpendicular as possible to the PCB running direction during soldering. The long axes of SOT and SOP should be parallel to the PCB running direction. Widen the pad of the last pin of the SOP (design a scratch pad).

b) The components of the plug-in components shall be formed according to the hole pitch of the PCB and the assembly requirements. For example, the short-insertion single-welding process is adopted, and the lead of the soldering surface component is exposed to the surface of the PCB by 0.8 to 3 mm, and the component body is required to be positive when the device is inserted.

c) According to the PCB size, the layer, the number of components, the presence or absence of placement components, etc., the preheating temperature is set, and the bottom temperature of the PCB is 90-130.

d) The tin wave temperature is 250 +/- 5 ° C, and the welding time is 3 to 5 s. When the temperature is slightly lower, the conveyor speed should be slower.

f) Replace the flux.

a) The solder joints of the components, the leads, the pads of the printed board substrate are oxidized or contaminated, or the PCB is wet.

b) The adhesion of the metal electrode at the end of the Chip element is poor or a single-layer electrode is used to cause a capping phenomenon at the soldering temperature.

c) The PCB design is unreasonable, and the shadow effect caused by Wave Soldering causes leakage welding.

d) PCB warpage, which makes the PCB tilt position and wave soldering poor contact.

e) The sides of the conveyor are not parallel (especially when using a PCB transmission), so that the PCB is not parallel to the peak contact.

f) The peaks are not smooth, and the heights on both sides of the peaks are not parallel. In particular, if the tin-wave nozzle of the electromagnetic pump Wave Soldering Machine is clogged with oxide, the peak will appear zigzag, which is easy to cause leakage welding and cold welding.

g) Flux activity is poor, resulting in poor wetting.

h) The preheating temperature of the PCB is too high, causing the flux to carbonize and lose its activity, resulting in poor wetting.

a) Use the components first-hand first, do not exist in a humid environment, and do not exceed the specified date of use. Cleaning and dehumidifying the PCB;

b) Wave soldering should select surface mount components with three layers of end structures. The component body and solder joints can withstand temperature shocks of more than two 260 ° C wave soldering.

c) When the SMD/SMC adopts wave soldering, the layout and arrangement direction of the components should follow the principle of small components in front and avoid mutual occlusion. In addition, it is also possible to appropriately lengthen the remaining pad length after the component is overlapped.

d) The PCB warpage is less than 0.8 to 1.0%.

e) Adjust the horizontal level of the wave soldering machine and the conveyor belt or PCB carrier.

f) Clean the peak nozzle.

g) Replace the flux.

h) Set the proper preheat temperature.

a) The preheating temperature of the PCB is too low, so that the temperature of the PCB and the component is low, and the components and the PCB absorb heat during soldering;

b) the soldering temperature is too low or the belt speed is too fast, so that the viscosity of the molten solder is too large;

c) The peak height of the electromagnetic pump wave soldering machine is too high or the lead is too long, so that the bottom of the pin cannot be in contact with the peak. Because the electromagnetic pump wave soldering machine is a hollow wave, the thickness of the hollow wave is 4 to 5 mm;

d) poor flux activity;

e) The soldering element lead diameter and the insertion hole ratio are incorrect, the insertion hole is too large, and the large pad absorbs a large amount of heat.

a) preheating temperature according to PCB, board layer, component number, presence or absence of mounting components, preheating temperature is 90-130 ° C;

b) Tin-wave temperature is 250 +/- 5 ° C, welding time is 3 ~ 5S. When the temperature is slightly lower, the conveyor speed should be slower.

c) The peak height is generally controlled at 2/3 of the PCB thickness. Pin-on component lead molding requires the pin to expose the PCB soldering surface 0.8 to 3 mm

d) replacing the flux;

e) The hole diameter of the insertion hole is 0.15 to 0.4 mm larger than the diameter of the lead wire (the lower lead takes the lower limit and the thick lead takes the upper line).

a) Dirty surface: mainly due to high solid content of flux, excessive coating amount, too high or too low preheating temperature, or due to too dirty conveyor belt claws, excessive oxides and tin slag in the solder pot, etc. of;

b) PCB deformation: generally occurs in large-size PCBs due to large weight of large-size PCBs or uneven weight due to uneven component placement. This requires PCB layout to make the components evenly distributed, and design the process side in the middle of the large PCB.

c) Loss of film (lost film): poor quality of patch adhesive, or incorrect curing temperature of patch adhesive. If the curing temperature is too high or too low, the bonding strength will be lowered. High temperature impact and peak shear force cannot be obtained during wave soldering. The role of the placement component in the pot.

d) Unexpected defects: solder joint grain size, internal stress of solder joints, internal cracks in solder joints, brittle solder joints, poor solder joint strength, etc., require X-ray, solder joint fatigue test and other tests. These defects are mainly related to soldering materials, adhesion of PCB pads, solderability of solder joints or leads of components, and temperature profiles.