Gents, I have found a low cost solution to CM690 and probably other casing's dust accumulation problem.

I found this at DAISO



I use a transparent plastic sheet as the frame for air intakes at the side panel and front grille. I cut the filter and affix it to the plastic frame using a double-sided tape.



Here's the front grille. I use the grille's bent metal as a hook to hold the frame of the filter. For the side panel filter, I cut the plastic sheet into a 120mm x 120mm square shape and cut 4 triangles inside it, creating an "X" in the middle. I had to make a frame to prevent the filter from touching the fan blades. I put double-sided tape on all side and the "X" to make sure it kept the filter in place.



I also place the filter at the bottom air intake and PSU air intake. Since the casing already have a mesh filter there, I did not make another frame. I cut the filter according to the size of the existing mesh filter, affix a small double-sided tape to keep it in place and put the dust filter in between the casing and the hard mesh filter. It fits rather nicely.  I did not use a lot of the filter for this modification. There are still a lot of spares and I intent to use them as replacement when the filters get dirty.

The results:

           
I have to say the results are quite spectacular. The dust filter dissipated the blue LED light from the front fan and creates a rather nice uniform glow. The filter doesn't impede the airflow so much. Placing my hand in front, I can still feel the air going quite strong into the casing. And the best thing is, the insides of my casing so far, are clean and dust free.

Total Cost of materials:

Dust filter  RM  5.00 (DAISO) 
Transparent Plastic  RM  5.00 (DAISO)
Thin Double-sided tape RM  1.50
Total:  RM 11.50

I use a transparent plastic sheet as the frame for air intakes at the side panel and front grille. I cut the filter and affix it to the plastic frame using a double-sided tape.



Here's the front grille. I use the grille's bent metal as a hook to hold the frame of the filter. For the side panel filter, I cut the plastic sheet into a 120mm x 120mm square shape and cut 4 triangles inside it, creating an "X" in the middle. I had to make a frame to prevent the filter from touching the fan blades. I put double-sided tape on all side and the "X" to make sure it kept the filter in place.



I also place the filter at the bottom air intake and PSU air intake. Since the casing already have a mesh filter there, I did not make another frame. I cut the filter according to the size of the existing mesh filter, affix a small double-sided tape to keep it in place and put the dust filter in between the casing and the hard mesh filter. It fits rather nicely.  I did not use a lot of the filter for this modification. There are still a lot of spares and I intent to use them as replacement when the filters get dirty.

The results:

           
I have to say the results are quite spectacular. The dust filter dissipated the blue LED light from the front fan and creates a rather nice uniform glow. The filter doesn't impede the airflow so much. Placing my hand in front, I can still feel the air going quite strong into the casing. And the best thing is, the insides of my casing so far, are clean and dust free.