5 ms·

A nice video, though it missed one of the most interesting aspects of BGA packages: their ability to self-centre during soldering. If the misalignment is less

by femto 2y ago

A nice video, though it missed one of the most interesting aspects of BGA packages: their ability to self-centre during soldering. If the misalignment is less extreme than in the video, surface tension will pull the BGA package into alignment. Here is an example https://www.youtube.com/watch?v=dz7ltWBDm7U https://www.youtube.com/watch?v=dz7ltWBDm7U Notice how in the second part of the video, once the solder has melted, the body of the BGA moves so it is correctly centred over the PCB pads. This is happening by itself, without an external influence pushing the chip into position.

brianpan 2y ago
Surface tension for the win. In the extreme misalignment example they also did not use flux so I guess they were purposefully showing what NOT soldered looks like. They did show how the solder flows in the "too much solder paste" example.
kayfox 2y ago
This is true for most surface mount packages, the surface tension of the solder will usually center the parts in their pads during reflow.
- xondono 2y ago
  This. In my experience QFN-like packages self center better than comparable BGAs, it’s just that BGAs in general are big so they are easy to line up. Small BGAs can be hell to hand solder.
  - aidenn0 2y ago
    I find SOICs to be by far the most forgiving; off by anything less than half the pitch and it tends to jump into place.
- dragontamer 2y ago
  In fact, the force of self centering is more a problem for small 0402 parts!!!! The force is so strong, it can 'Tombstone' the piece during reflow. This is partially why 0402 is used rather than the more electrically convenient 0204. It's easier to tombstone on the long edge. ------- Also, if you don't care about tombstoning but need the better parasitics of a 0204 capacitor or the better heat capacities of a 0204 resistor, try them out!!
beaglesss 2y ago
And if it doesn't work on all pads, you may need an X-ray to figure it out.
- the__alchemist 2y ago
  Live by the balls; die by the balls. Most of my soldering errors are from incorrect amount of solder, so, BGA tends to work better than other footprints.
- tirant 2y ago
  In BGA soldering, the concept of partial alignment doesn’t really happen. Here’s why: In a 2D plane (which is the PCB), only two points are needed to define alignment. If two solder balls are aligned with their pads, surface tension in the reflow process ensures the entire BGA package aligns with the rest of the pads automatically. Surface tension acts on all the solder balls, pulling the package into place along both the X and Y axes. So once the first few balls are in place, the whole thing “snaps” into alignment. Misaligning only some pads while others are perfectly aligned isn’t possible unless something’s seriously wrong, like a warped board or damaged package. It’s an all-or-nothing situation—either everything aligns, or nothing does.
  - yetihehe 2y ago
    > Misaligning only some pads while others are perfectly aligned isn’t possible It's possible when your pcb-making process is on the odge of what designer wanted. Some pads on some boards may be not perfectly aligned in such cases. Or the board was heated not enough or in too short time and not all balls melted properly. Or it cracked under stresses because designer put too much vias in one place near the chip. > It’s an all-or-nothing situation—either everything aligns, or nothing does. In theory, practice and theory agrees. In practice, it sometimes does not.
    - loup-vaillant 2y ago
      I believe you forgot to quote "unless something’s seriously wrong". Your counter examples seem to describe exactly that: something going seriously wrong.
dyno12345 2y ago
you have to have the right amount of solder on 100% of the pads for this to work correctly though
- avar 2y ago
  Do you? I'd imagine you can have too little on some of the pads, such that the melted material doesn't make contact. As long as others pads have enough they'd pull the BGA into place, and at that point those pads would make contact and complete the solder.
saagarjha 2y ago
As someone who doesn't solder or really do much with hardware at all, this answers a longtime question of mine. I always wondered how people got all their stuff aligned perfectly ;)
systems_glitch 2y ago
Yup, when we rework BGA boards it's sufficient to go off the silkscreen outline of the package, if the board has one. Also the cool-down BGA effect they showed is a lead-free thing, you don't see that on leaded solder balls unless something is wrong.

by femto 2y ago

brianpan 2y ago

Surface tension for the win. In the extreme misalignment example they also did not use flux so I guess they were purposefully showing what NOT soldered looks like. They did show how the solder flows in the "too much solder paste" example.

kayfox 2y ago

This is true for most surface mount packages, the surface tension of the solder will usually center the parts in their pads during reflow.

xondono 2y ago
This. In my experience QFN-like packages self center better than comparable BGAs, it’s just that BGAs in general are big so they are easy to line up. Small BGAs can be hell to hand solder.
- aidenn0 2y ago
  I find SOICs to be by far the most forgiving; off by anything less than half the pitch and it tends to jump into place.
dragontamer 2y ago
In fact, the force of self centering is more a problem for small 0402 parts!!!! The force is so strong, it can 'Tombstone' the piece during reflow. This is partially why 0402 is used rather than the more electrically convenient 0204. It's easier to tombstone on the long edge. ------- Also, if you don't care about tombstoning but need the better parasitics of a 0204 capacitor or the better heat capacities of a 0204 resistor, try them out!!

beaglesss 2y ago

And if it doesn't work on all pads, you may need an X-ray to figure it out.

the__alchemist 2y ago
Live by the balls; die by the balls. Most of my soldering errors are from incorrect amount of solder, so, BGA tends to work better than other footprints.
tirant 2y ago
In BGA soldering, the concept of partial alignment doesn’t really happen. Here’s why: In a 2D plane (which is the PCB), only two points are needed to define alignment. If two solder balls are aligned with their pads, surface tension in the reflow process ensures the entire BGA package aligns with the rest of the pads automatically. Surface tension acts on all the solder balls, pulling the package into place along both the X and Y axes. So once the first few balls are in place, the whole thing “snaps” into alignment. Misaligning only some pads while others are perfectly aligned isn’t possible unless something’s seriously wrong, like a warped board or damaged package. It’s an all-or-nothing situation—either everything aligns, or nothing does.
- yetihehe 2y ago
  > Misaligning only some pads while others are perfectly aligned isn’t possible It's possible when your pcb-making process is on the odge of what designer wanted. Some pads on some boards may be not perfectly aligned in such cases. Or the board was heated not enough or in too short time and not all balls melted properly. Or it cracked under stresses because designer put too much vias in one place near the chip. > It’s an all-or-nothing situation—either everything aligns, or nothing does. In theory, practice and theory agrees. In practice, it sometimes does not.
  - loup-vaillant 2y ago
    I believe you forgot to quote "unless something’s seriously wrong". Your counter examples seem to describe exactly that: something going seriously wrong.

dyno12345 2y ago

you have to have the right amount of solder on 100% of the pads for this to work correctly though

avar 2y ago
Do you? I'd imagine you can have too little on some of the pads, such that the melted material doesn't make contact. As long as others pads have enough they'd pull the BGA into place, and at that point those pads would make contact and complete the solder.

saagarjha 2y ago

As someone who doesn't solder or really do much with hardware at all, this answers a longtime question of mine. I always wondered how people got all their stuff aligned perfectly ;)

systems_glitch 2y ago

Yup, when we rework BGA boards it's sufficient to go off the silkscreen outline of the package, if the board has one. Also the cool-down BGA effect they showed is a lead-free thing, you don't see that on leaded solder balls unless something is wrong.