Guideline for Tenting Interstitial BGA Vias
It is difficult to give a complete recommendation on via tenting without an idea what process conditions are required (ex: wave pass, double reflow, rework etc.). Via Pads (as Test Points)
- On Bottom
The need to use the bottom side vias pads as test points is acceptable in all cases except wave. If using PTHs and not blind / buried vias, the via is connected from top to bottom and so the bottom side of the BGA via can be used for test. The bottom side vias do not need to be covered for std. SMT or double side reflow or even rework.
- Case of Wave Solder Process
In the case of wave, the vias would have to be taped off or use a peelable solder mask (these are in use for Au finger connectors on a regular basis). Via Pads (underneath BGA)
- On Top
The via pads on the top (underneath) the BGA should be covered to prevent the solder from wicking into the PTH. The via pads on the top side cannot be used anyway since they are covered by the device.
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