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Copper Filled Vias
16 September 2009
CC Electronics Europe Limited can now offer copper filled vias.
An ever increasing number of via holes are being used in pcb design and as with most electronics, they are getting smaller. A via hole is a connection through the board or only to selected layers of the board. They are used to make interconnections but not required to have leads soldered through the holes.
The via hole size normally ranges between 0.010" - 0.014" in a pad of 0.014-0.018". Via holes can have the same solder mask apertures as plated through hole which is 0.004-0.006" larger than the pad. Blind via holes are normally a hole produced by laser or controlled depth drilling that make a connection from a surface pad to one or more inner layers but do not exit the other side of the board, hence the name blind via. These vias normally range in size between 0.008 -0.014”
Some designs can benefit from having vias filled rather than just leaving them open on the surface of the board after plating. Filling of vias can be achieved with epoxy, paste, plated with copper or tented with solder mask. Normally referred to as filled vias as opposed to plugged, capped, and tented, which are other terms often used in the industry; these are terms associated with masks, however these vias are not necessarily filled with any material.
Benefits that may be achieved through filling a via hole are:
Allowing void free joints as a result of vias in pad assembly. If nothing can outgas form the via during reflow soldering this design feature will not contribute to voiding often found in Ball Grid Array (BGA) joints. If through vias and blind vias are left open, paste volatiles will enter the hole and make evaporation difficult.
Provide reliable flat test points for electrical probing. Open vias on the surface of pads can lead to damage of test pins particularly flying probe needles at printed board fabrication or during final assembly. They do not make for the most reliable test point.
Improving via hole reliability can be achieved by supporting the plated through hole during temperature and power cycling. With a greater number of vias used in thermal pads for better heat dissipation this is a reality. With the use of unfilled vias under Land Grid Arrays (LGA) this has lead to the increase of voiding and component floating on the surface of the pad.
Improved vacuum hold down of the printed board assembly during electrical test
Tenting of vias during the solder mask process is a step often used. To cover larger holes tenting vias with one or even two solder mask printing steps is quite common but adds to the cost in manufacture. A two step process will still not guarantee that the air in the via does not expand and cause a broken bubble on the surface of the hole during soldering.
It is important to confirm what is specifically required from your via design and specification and communicate this to us so there is no confusion. We will recommend a method that is more appropriate and of course reduce the final cost of your product.
Need more information? Please call our Customer Technical Manager Tom Parker 07979 245850
+44 (0)1606 861155
Wharton Ind Estate, Nat Lane, Winsford, Cheshire, CW7 3BS
