Printed Circuit Design & Fab - November 2007 - (Page 39)

TABLE 4. BGA technology chart for 0.4-, 0.5- and 0.65-mm pitch BGA parts. BGA PIN BGA PITCH BALL DIA 0.4 0.5 0.65 0.65 0.25 0.3 0.4 0.4 BGA LAND LAND SIZE 0.25 0.275 0.4 0.425 LAND HOLE HOLE SIZE 0.125 0.15 0.15 0.2 PLANE CLEARANCE 0.35 0.425 0.5 0.575 TRACE WIDTH 0.05 0.075 0.1 0.075 TRACE/ TRACE SPACE 0.05 0.075 0.1 0.075 TRACE/ VIA SPACE 0.05 0.075 0.1 0.075 TRACE/ LAND SPACE 0.05 0.075 0.075 0.075 ROUTE GRID 0.05 0.05 0.05 0.05 PART PLACE GRID 0.5 0.5 1 1 It is important to fill the via the routing solutions for the TABLE 5. Non-collapsing BGA ball land calculations. hole with a conductive or 0.5-mm pitch BGA. However, NOMINAL BALL INCREASE NOMINAL LAND LAND VARIATION non-conductive material. The the through-hole via-in-land DIAMETER DIAMETER filling material will depend is actually a less expensive 0.75 15% 0.85 0.90 - 0.80 on the process that the PCB alternative as long as the PCB 0.65 15% 0.75 0.80 - 0.70 fabrication facility uses. If you thickness is 1 mm or less to 0.60 15% 0.70 0.75 - 0.65 call out a specific fill material maintain a good aspect ratio. 0.55 15% 0.65 0.70 - 0.60 such as a vendor’s silver Double-layer blind via 0.50 10% 0.55 0.60 - 0.50 epoxy on your fabrication technology is preferred because notes, the manufacturer layer-to-layer controlled 0.45 10% 0.50 0.55 - 0.45 might have to special order impedance causes layer 2 to act 0.40 10% 0.45 0.50 - 0.40 that via fill material, and this as the ground plane or reference 0.35 10% 0.40 0.45 - 0.35 can increase the fabrication plane to the layer 1 signals. 0.30 10% 0.35 0.40 - 0.30 cost. This is an area where Layer 3 is typically where the 0.25 10% 0.30 0.35 - 0.25 communication with the signal must go. Layer 3 can 0.20 5% 0.21 0.26 - 0.16 fabricator can help determine then transition through the rest what is the best and most of the inner signal layers using 0.17 5% 0.18 0.22 - 0.13 cost-effective via fill material blind via technology and the 0.15 5% 0.16 0.21 - 0.11 that will meet your design layer construction techniques objectives. noted below. This technology When using via-in-land technology, is for 0.4-, 0.5- and 0.65-mm pitch BGA FIGURE 10 is a filled and capped solder mask is defined on a 1:1 scale components. via (Type VII Via); a Type V via with a on the BGA side of the PCB and tented Today, the second finest pitch BGA secondary metallized coating covering or covered with solder mask on the in the industry is 0.5 mm. Trace/spacing the via. The metallization is on both opposite side to protect the routed traces. of 0.075 mm is not yet mainstream, but sides. This technique is designed for However, you could use 1:1 scale solder PCB fabrication companies are quickly future via-in-land technology for mask on both sides if you need to use the getting up to speed on this technology. 0.4- and 0.5-mm pitch and current bottom side for a test fixture. The two outer rows of a 0.5- and 0.650.65-mm pitch BGA devices when a A solder mask defined land is used mm pitch BGA are routed to a via through-hole in a BGA land is used. fanout on the external layer and blind vias, or through vias are only used on the inner rows. Non-Collapsing Ball BGA Components TABLE 5 can be used for land size calculations for non-collapsing BGA balls. It is very important to note that IPC prefers the maximum material condition for all BGA land sizes, meaning that the maximum land variation diameter is used; the nominal land diameter is not. FIGURE 9 shows a 0.5-mm pitch non-collapsing BGA ball. Instead of shrinking, the non-collapsing land size gets larger to handle the solder volume that creates the solder joint. This technology is new to the electronics industry and was created as a solution for lead-free BGA balls. NOVEMBER 2007 PRINTED CIRCUIT DESIGN & FAB 39 http://www.pcb-pool.com http://www.pcb-pool.com http://www.free-pcb-software.com http://www.pcb-pool.com

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Printed Circuit Design & Fab - November 2007

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