Design Solutions for Fine Pitch BGA

ACDi’s engineering services team is constantly working with our customers to produce reliable PCB designs with the lowest fabrication costs for our customers. A recent design highlights ACDi’s expertise in the routing of fine pitch BGAs, and the extra effort to reduce a customer’s board costs by up to 20%.

Problem:

Our customer came back to ACDi for a re-design of a board we had previously laid out. The changes to the board involved adding a .5mm pitch Toshiba flash card. The existing stack-up was a 16 layer board with all thru-vias. DFM constraints do not allow for thru-vias small enough to fit inside the pad array of this fine-pitch part. Alternative fan-out methods would need to be used.

Solutions:

1. Mirco vias- 10mil pads with 5 mil laser drills, centered in the BGA pads, layer 1-2

2. 3 mil traces with 3 mil spacing- outer two rows of pins fanned out on component side between pins

3. Plow-through routing- ACDi’s proposed solution

Option 1 would have changed the stack-up of the design, resulting in higher fabrication costs (due to micro-via), and adjusting routing of existing circuits that had already been proven to work

Option 2 would have increased the cost to fabricate the board due to the tighter than industry-standard spacing requirements, and potentially would have caused issues at assembly

Resolution:

Option 3 ACDi realized there were 7 pins that could not be fanned out with through-vias that were necessitating these proposed solutions. We reached out to Toshiba to determine the pin-use of the adjacent pins. After confirmation from Toshiba that some of these pins were no connects inside of the IC, we were able to “plow-through” route these adjacent pads, and fan out directly to thru-via. The existing stack-up was maintained, the fabrication limits did not increase, and ACDi was able to reduce board costs by up to 20% while still outputting a quality design.

Download the full case study below.

COST-SAVING-DESIGN-SOLUTIONS-FOR-FINE-PITCH-BGA

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