Pinhole and porosity both represent the solder joints have air bubbles, but not yet expanded to the surface, most of them occur at the bottom of the substrate, when the bottom of the bubble completely diffuse burst before the condensation, that is, the formation of pinhole or porosity. The difference between pinholes and porosity is that pinholes are smaller in diameter.
Causes:
Organic contaminants on the substrate or on the pins of the part. Such contaminated materials come from automatic insertion machines, pin forming machines and from factors such as poor storage.
Substrates containing water vapor from plating solutions and similar materials. If the substrate is made of cheaper materials, it is possible to inhale such water vapor and generate enough heat during soldering to vaporize the solution, thus causing porosity.
Substrates stored too much or improperly packaged, absorbing water vapor from the nearby environment.
Moisture in the flux bath.
Excessive moisture in the compressed air used for foaming and hot air knife.
Preheating temperature is too low to evaporate water vapor or solvent, once the substrate enters the tin furnace, instant contact with high temperature, and burst.
Tin temperature is too high, encounter with moisture or solvent, immediately burst.
Solution:
Removal of organic contaminants from pins with common solvents; as silicone oil and similar products containing silicon are difficult to remove, if the problem is found to be caused by silicone oil, consideration must be given to changing the source of the lubricant or release agent.
Baking the substrate in an oven prior to assembly to remove any moisture contained in the substrate.
baking the substrate in the oven before assembly.
periodic flux changes.
the need for a water filter for compressed air and regular exhaust.
Adjusting the preheating temperature.
Turn down the temperature of the solder oven.
Causes:
Improper time a temperature relationship.
Incorrect solder composition.
Mechanical vibration before solder cooling.
Tin is contaminated.
Solution:
Adjusting the conveyor belt speed and correcting the solder preheat temperature to establish the proper time-to-temperature relationship.
Checking the solder composition to determine the type of solder and the proper soldering temperature for a given alloy.
Inspecting the conveyor belt to ensure that the substrate is not bumped or shaken during soldering and solidification.
Checking the type of impurity causing contamination and reducing or eliminating contaminated solder in the bath by appropriate methods (dilution or replacement of solder)
Causes:
Conveyor belt speed is too fast.
Welding temperature is too low.
Secondary welding waveform is low.
Improper waveform or improper waveform and plate angle and improper waveform at the outgoing end.
Contamination of the plate surface and poor weldability.
Solution:
Slow down the conveyor belt speed; the latest point on its
Adjusting the temperature of the tin furnace.
readjusting the secondary welding waveform.
Readjusting the waveform and the angle of the conveyor belt.
Clean the PCB board surface to improve its solderability.
Component solder ends and pins are surrounded by too much solder, the wetting angle is greater than 90 °.
Causes:
PCB preheating temperature is too low, components and CB absorb heat when soldering, so that the actual soldering temperature is reduced.
Poor activity of flux or too small specific gravity.
Poor solderability of the pad, cartridge hole or pin, which cannot be fully wetted and the resulting air bubbles wrapped in the solder joint.
A decrease in the proportion of tin in the solder, or a high composition of impurities Cu in the solder, which increases the viscosity of the solder and makes it less liquid.
Too much solder residue.
The welding temperature is too low or the conveyor belt speed is too fast, making the viscosity of the molten solder too large.
Solution:
Set the preheating temperature according to the PCB size, board layer, how many components, whether there are mounted components, etc. The temperature of the bottom surface of the PCB is 90~130℃.
Replace flux or adjust the appropriate ratio.
Improve the processing quality of PCB, components first come first use, do not store in humid environment.
tin ratio of less than 61.4%, add some pure tin in appropriate amounts impurities should be replaced when the solder is too high.
residue should be cleaned up at the end of each day's work.
Control the tin wave temperature at (250 ± 5) ℃, welding time 3 ~ 5s.
Causes:
Poor component lead solderability, pad is too large (except for the need for large pads), pad hole is too large, the welding angle is too large, the transmission speed is too fast, the tin pot temperature is high, the flux coating is not uniform, the solder does not contain enough tin.
Solution:
Solve the lead solderability, design to reduce the pad and pad hole, reduce the soldering angle, adjust the transmission speed, adjust the temperature of the tin pot, check the pre-application of flux device, laboratory test solder content.
