judpoir
Newbie level 1
Hi everyone,
I am currently in contact with a PCB manufacturer for a microvia 1+8+1 board, so microvias are present on top and bottom (6mils finished holes and 13 mils for a depth of 4 mils).
Among other remarks, the manufacturer highlights possible assembly problems due the fact that my microvias are too close to 0402 component pads. Actually I have the habit (and the need in this case due to the board density) to put vias very close to decoupling capacitor pads to enhance power integrity (lowers the inductance of the tracks to the cap): for these caps, the annular ring of the microvia is overlapping the 0402 cap pads but the via hole remains oustide the perimeter of the pad. The manufacturer warns me that I should expect solder paste flowing from the 0402 component through the microvia during assembly which would result in a bad solder joint for the component pad. While I'm aware of the problem for though-hole vias, I thought that microvias with such a small cavity (6mils diameter - 4mils deep) would be filled before too much of the solder paste would leave the component pad.
Four solutions have been proposed so far:
- Putting the microvias further apart from the component pad to leave a solder mask barrier of at least 6 mils wide to isolate solder paste. This would be pretty difficult since I don't have much place left and would require much rework.
- Putting vias inside pads (with no via filling) is another solution proposed by the manufacturer. I don't know if this would work because solder paste still has the opportunity of mowing down the via hole. And if not, I heard that void problems could occur inside the hole (I heard this could be solved by off-centering the via hole from the pad center but I don't have many information about that).
- Via filling which is of course pretty expensive but would solve the problem for sure. I would agree but, guess what, my boss does not
- The laziest one: leaving my baord as it is. Indeed I'm not sure that it would be an issue that assemblers couldn't solve especially when the volume to fill inside the microvia is so small.
Any input, new idea, experience on that matter would be more than welcome
Thank you advance!
Alexis
I am currently in contact with a PCB manufacturer for a microvia 1+8+1 board, so microvias are present on top and bottom (6mils finished holes and 13 mils for a depth of 4 mils).
Among other remarks, the manufacturer highlights possible assembly problems due the fact that my microvias are too close to 0402 component pads. Actually I have the habit (and the need in this case due to the board density) to put vias very close to decoupling capacitor pads to enhance power integrity (lowers the inductance of the tracks to the cap): for these caps, the annular ring of the microvia is overlapping the 0402 cap pads but the via hole remains oustide the perimeter of the pad. The manufacturer warns me that I should expect solder paste flowing from the 0402 component through the microvia during assembly which would result in a bad solder joint for the component pad. While I'm aware of the problem for though-hole vias, I thought that microvias with such a small cavity (6mils diameter - 4mils deep) would be filled before too much of the solder paste would leave the component pad.
Four solutions have been proposed so far:
- Putting the microvias further apart from the component pad to leave a solder mask barrier of at least 6 mils wide to isolate solder paste. This would be pretty difficult since I don't have much place left and would require much rework.
- Putting vias inside pads (with no via filling) is another solution proposed by the manufacturer. I don't know if this would work because solder paste still has the opportunity of mowing down the via hole. And if not, I heard that void problems could occur inside the hole (I heard this could be solved by off-centering the via hole from the pad center but I don't have many information about that).
- Via filling which is of course pretty expensive but would solve the problem for sure. I would agree but, guess what, my boss does not
- The laziest one: leaving my baord as it is. Indeed I'm not sure that it would be an issue that assemblers couldn't solve especially when the volume to fill inside the microvia is so small.
Any input, new idea, experience on that matter would be more than welcome
Thank you advance!
Alexis