What is Wicking and how to test it

2020-01-16 14:48Writer: qyadminReading:

What is Wicking


      Plating that migrates along the glass fiber insulation layer called Wicking.
 
      Wicking measured after plating the test panel.
      A cross section of the processed holes made. and where high levels of wicking appear a measurement taken. Additionally, wicking confirmed more when a cross-section done at 90deg. against the glass fiber in general.
The distance measured base line of the wall of the hole to the largest point of ingress
 
      Wicking is one of the important factors. that cause the internal short of Printed Circuit Board (PCB). and restrict the pitch of holes. In this paper, orthogonal experimental design method. used to study the effect of five drilling parameters on the wicking. The five factors are rotation speed, feeding speed, retracting speed. drill life and stack number. The result shows that the order of the influencing factors is as follows: stack number. drill life rotation speed, retracting speed, feeding speed. It found that the greatest parameters combination is rotation speed of 150 kr/min. feeding speed of 38 mm/sec, retracting speed of 280 mm/sec. drill life of 1600 hits and stack number of 1 PNL/stack.
 
      Wicking is one of the important factors that. cause the internal short of Printed Circuit Board (PCB). and restrict the pitch of holes. In this paper, orthogonal experimental design method. used to study the effect of five drilling parameters on the wicking. The five factors are rotation speed, feeding speed, retracting speed. drill life and stack number. The result shows that the order of the influencing factors is as follows. stack number, drill life rotation speed, retracting speed, feeding speed. It found that the greatest parameters combination is rotation speed of 150 kr/min. feeding speed of 38 mm/sec, retracting speed of 280 mm/sec, drill life of 1600 hits and stack number of 1 PNL/stack.

what is solder wicking

 
     Solder wicking defined as solder climbing up. on a lead (component, connector, external wire). Wicking is a redistribution of solder away from the intended joint. and this caused by the solder's surface tension.
 
     Knowing how to use a solder wick, which braided copper wire. that allows you to remove solder from joints you need to alter. is important if you work on electronics. Solder wick is especially useful if you need to remove solder from a circuit board or components. If you’re new to soldering, you should have solder wick ready in case you need to correct any mistakes you make. It’s easy to use a solder wick, and it can save you from having to replace parts that weren’t soldered .
 

 Wicking Evaluation Method

       Wicking is measured after plating the test panel.A cross section of the processed holes is made and where high levels of wicking appear a measurement is taken. Additionally, wicking is confirmed more clearly when a cross-section is done at 90deg. against the glass fiber in general.The distance is measured base line of the wall of the hole to the maximum point of ingress, as shown in the figure below.
 
      IPC requires that wicking measured. from the drilled hole edge to the point where the wicking ends. This might result in a false result where you don’t measure the wicking itself. In the new and revised edition of the Automotive Addendum. we will precise that the measurement should start and stop where the wicking start and stops. Only then will the results be correct.
 
        Standards for PCB production specifications need to be alive and kicking. facilitating a modern production that meets the demands of today, not the ones in the past. As chair and member in several task groups, I know how much work lays behind a standard. The whole idea. with task groups is to work dedicated towards an improvement, securing that all needs. and consequences considered and watch the challenges from all stages of production. We need to extract knowledge from production files. and convert it into useful information to improve the standards. so they match the demands not only from IPC but also the industry.

 

pcb wicking
 

   

pcb wicking cause reason


     Have you ever wondered why sometimes you have poor Solder joints on your PCB’s!

      One of the main reasons is that the Solder Paste flows away from the pad on the PCB during Reflow. this known as Solder Escape, Solder Wick or Solder Drainage.

      Why does this happen, well there are a few reasons. but they are all the result of Thermal Dissipation during the Reflow process.  the heat flows away from the pad on the PCB to a larger Thermal conductive area. that’s connected to the pad and unprotected by a Soldermask Dam, these include:

Via Holes
Copper Areas
Larger Tracks
an (animation) of a Via Hole. that is too close to a SM pad and thus has no Soldermask Dam to stop the Solder Paste escaping into the hole.

 

pcb wicking solution


       This PCB assembly challenge involved attaching a solar panel to one side of a pad using solder paste with a. pass through an SMT reflow soldering oven.

Solder wicking 1
       Solder wicking through the unmasked. vias to the back side forms unacceptable “bumps” on top of the vias

      The attachment or bond itself wasn’t the issue; but after the first trial runs. it was clear that solder wicking through the unmasked vias was going to be. Solder would wick through the unmasked vias to the back side and form “bumps” on top of the vias.

       These bumps made the surface nonplanar and of course were unacceptable. It wasn’t an issue of using excess solder paste. But the “wicked wicking” had to stopped, or at least prevented.

      But how? to keep the solder where we wanted it to remain during reflow, we had to find a way to prevent. it from wicking up, collecting at the opposite ends of the vias and forming bumps. We had to find a solution that was simple. temporary, and tolerant of reflow soldering temperatures. The answer was Kapton polyimide tape, a familiar product to PCB assemblers for many years. and a material that does not degrade at reflow temperatures.

Kapton tape - molten solde
       Kapton tape applied to cover the unmasked vias. it will block the molten solder from leaking through.

      Kapton tape applied to cover the unmasked. vias to block the molten solder from leaking through the vias to the back side during reflow. After reflow and cooling, it was a simple matter to peel off the tape. This temporary masking solution worked. there were no more solder bumps on the back side of the assembly. and the cost of the fix time and material was very low.

temporary masking solution PCB
      This temporary masking solution worked. there are no more solder bumps on the back side of the assembly.


how to prevent solder wicking

 
For those less familiar with this phenomena a few words to the theories. and root causes of solder wicking which defined as solder climbing up on a lead:
-The pad reaches the liquidus temperature later than the lead. thus the melted solder is
tightened completely by the lead (wicking-up phenomena)
-The solder alloy pulls to the hotter surface if enough wettability
- Leads are melting faster than rivet solder joint . the delayed liquefaction of solder paste. at the rivet solder joint pulls the leads away from pads
-All non-wetting problems like plating too thin or contamination/oxidation can cause wicking-up
In preparation of testing the printed circuit board consideration . given to following conceivable wetting parameters:
-Temperature difference
-Wettability of pad
-Heat sink at conductor
-Gap dimension between pad/lead
-Melting time of solder at rivet
The major conclusions to the above:
-The heat sink had to heated up first, and increased convection heat had to applied from the bottom.
-For the following test a well-proven 8-zone (5 pre-heat. 3 peak zones) forced convection reflow oven SMT
-Quattro Peak L Plus (N2) selected suitable for processing very complex boards. with greatest process stability and unmatched reproducibility. This reflow oven model also features perfect heat transfer, excellent zone separation. and achieving unique cross and load profile performance.
-The manufacturer of this reflow oven is globally active SMT Maschinen. und Vertriebs GmbH, Wertheim,
 

Tags:
drilling parameters. high density. circuit board. printed circuit. pcb assembly. standard pcb. pcb layout. pcb glossary. pcb manufacturing. base material. solder mask. wave soldering. pcb industry. manufacturing process. hole wall. 
 


Related articles

pcb backup board
pcb back up board backup material