BGA interposer at 0.5 mm pitch: lessons from practice

Interposer for BGA 0.5 mm pitch: not right the first time...

We made an interposer for a BGA with 0.5 mm pitch.

The datasheet specified:

• Use pads of 0.3 mm.
• Via 0.15 mm (expensive!) and annular ring (each side 0.075 mm) quite narrow (3 mil)
• This unfortunately made the interposer expensive and slow to arrive (11 working days).
• Moreover, the vias were not filled, which would have taken even longer.

After that, we had problems manually filling the vias ourselves. It was very difficult. The liquid solder tin was bubbling in the vias like pea soup!

In the end, we managed to get 1 interposer working. But it should be clear that this is not the right approach.

What we're going to try next:

• Enlarge pads to 0.35 mm.
• Drill hole to 0.2 mm (which is significantly cheaper and faster)
• Choose 'Via in Pad' instead of 'filled via' at the PCB manufacturer
• Lead time: 5-5 working days and significantly cheaper.

Fingers crossed that the 0.35 mm pads haven't introduced a short.

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