Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Manufacturing/design issue: solder paste flowing from pads through microvias

Status
Not open for further replies.

judpoir

Newbie level 1
Joined
Jan 10, 2012
Messages
1
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Brussels
Activity points
1,303
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
 

If you sit the SMD components on the board into a glue droplet, and only then apply the soldering paste, the paste in fact helps good soldering. The paste is then washed away but soldered components stay.
 

as I understood it solder paste will only fill on capillery action so a blind micro shouldnt be a problem due to the fact that it would actually be a vacuum wouldnt it capilery needs an open end to force the air out doesnt it .
Or you could tell them to get ther office boy tocover all the offending vias with kapon tape
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top