Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Solder Ball Attach

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Solder Ball Attach (BGA) | 24 September, 2018

We are attaching 0.50mm diameter SAC 305 solder balls onto 0.38 diameter Au plated pins placed at a 0.80mm pitch (pins are pressed into a plastic insulator). A tacky flux is then stenciled onto the pins using a stencil with.a 0.38mm diameter aperture and 0.13mm thick SS.There can be up to 400 balls placed on a 0.80mm pitch on a 20X20 grid. After solder ball transfer the BGA’s are reflowed using a convection oven. The peak temp of the reflow profile is 237C, with time above liquidus (217C) at 59 seconds. The entire cycle is a approximately 3.5 minutes. The issue we are having is that after reflow many of the solder balls have not centered themselves onto the Au plated surfaces. This does not happen when attaching 63-37 eutectic balls. To solve this issue, we use a small brush to literally paint more flux onto the cooled solder balls, then reflow the parts a second time. After the re-fluxing and re-re-reflow the parts look awesome. Has anyone ever encountered this?

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Solder Ball Attach (BGA) | 28 September, 2018

The followings may be the factors from your description:

1. chain speed and motor speed? 2. is the tin content even? (more or less on one side, or thickness of steel mesh, size of opening) 3. Is there any exception in the pin? 4. is there any level of chain track? (for example, the central supporting mechanism is highly eccentric). 5. does the furnace itself have leveling and leveling? 6. if it is not in one direction, is the quality of solder paste made of impurities? May be you can share with a picture, then the problem can be more clear, and welcome to share more opinion with ALLPCB

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Solder Ball Attach (BGA) | 4 October, 2018

1. From your explanation it looks like you need more flux. Try to overprint a little or use 150um thick stencil 2. You should consider a little different profile - probably try to have a soak zone in the right alloy and flux range and give the part time to evenly preheat let the volatiles escape and have the balls centered.

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