Causes:
Component solder ends, pins, printed board substrate pads oxidation or pollution, PCB moisture.
Chip components end metal electrode adhesion is poor or the use of single-layer electrode, the phenomenon of decapitation in the welding temperature.
Unreasonable PCB design, shadow effect during wave soldering machine causing leakage of solder.
PCB warpage, making poor contact between PCB warp position and wave soldering.
non-parallelism on both sides of the conveyor belt (especially when using the PCB conveyor frame), making the PCB not parallel to the wave contact.
wave crest is not smooth, the height of both sides of the wave crest is not parallel, especially the electromagnetic pump wave soldering machine tin wave nozzle, if blocked by the oxide when the wave crest will appear jagged, easy to cause leakage, false soldering.
Poor flux activity, resulting in poor wetting.
PCB preheating temperature is too high, so that flux carbonization, loss of activity, resulting in poor wetting.
Solution:
Components first come first use, do not store in a humid environment, do not exceed the specified use date, clean and de-tide the damp PCB.
Wave soldering should choose surface mount components with three-layer end structure, the component body and solder end can withstand more than two times the temperature impact of 260℃ wave soldering.
SMD/SMC adopts wave soldering when the layout and layout direction of components should follow the principle that smaller components are in front and try to avoid blocking each other, in addition, it can also appropriately lengthen the remaining pad length after the lap of components.
PCB warpage less than 0.8 to 1.0 per cent.
Adjust the wave soldering machine and the lateral level of the transfer belt or PCB transfer frame.
cleaning the wave nozzle.
Replacing flux.
Set the proper preheat temperature.
Causes:
PCB preheating temperature is too low, so that the temperature of PCB and components is low, and components and PCB absorb heat when soldering.
Welding temperature is too low or conveyor speed is too fast, so that the viscosity of the molten solder is too large.
The wave height of the electromagnetic pump wave soldering machine is too high or the pin is too long, so that the bottom of the pin cannot contact the wave, because the electromagnetic pump wave soldering machine is a hollow wave, the thickness of the hollow wave is 4~5mm
poor flux activity.
Welding components lead diameter and cartridge hole ratio is not correct, cartridge hole is too large, large pad heat absorption.
Solution:
Set the preheat temperature according to PCB, board layer, how many components, whether there are mounted components, etc. The preheat temperature is 90~130℃.
Tin wave temperature is (250±5)℃, welding time 3~5s, when the temperature is slightly low, the conveyor speed should be adjusted to slow down some.
wave height is generally controlled at the PCB thickness of 23 inserted components pin forming requirements pin exposed PCB welding surface 0.8 ~ 3mm.
Replacement of flux.
The hole diameter of the cartridge hole than the lead diameter of 0.15 ~ 0.4mm (fine lead to take the lower limit, thick lead to take the upper limit).
SMA after welding will appear in individual solder joints around the light green small, such as ice high serious when there will also be nail cover size of the bubble, not only affect the appearance of quality, serious when it will also affect the performance. This defect is also a frequent problem in the reflow soldering process, but common to wave soldering.
Causes:
Solder resist film blistering root cause is the existence of gas or water vapor between the solder resist film and PCB substrate, these traces of gas or water vapor will be entrained in the different processes to which, when encountered when welding high temperature, gas expansion and lead to the delamination of the solder resist film and PCB substrate, welding, solder benefit temperature is relatively high, so the bubble first appeared around the pad.
One of the following reasons, will lead to PCB entrapment of water vapor.
PCB in the processing process often need to clean, dry before doing the next process, such as rot engraved should be dry before paste solder resist film, if the drying temperature is not enough at this time, it will be entrained with water vapor into the next process, high temperature in the welding and bubbles.
PCB processing before storage environment is not good, the humidity is too high, welding and no timely drying process.
In the wave soldering process, now often use flux containing water, if the PCB preheating temperature is not enough, the water vapor in the flux will be along the hole wall of the through-hole into the interior of the PCB substrate, its pad around the first to enter the water vapor, encountering high temperatures after welding will produce bubbles.
Solution:
Strict control of each production link, the purchased PCB should be inspected and warehoused, usually PCB at 260 ℃ within 10s should not appear bubbling phenomenon.
PCBs should be stored in a ventilated and dry environment for a period of no more than 6 months
PCBs should be placed in an oven at (120+5)°C for 4h pre-baking before soldering
Wave soldering in the preheating temperature should be strictly controlled, before entering the wave soldering should reach 100 ~ 140 ℃, if the use of flux containing water, its preheating temperature should reach 110 ~ 145 ℃ to ensure that the water vapor can be evaporated.
