Why Is The Rate Of Success For BGA Rework So Low When Compared To The Manufacturing Process?

[hihihi8]

As titled, how does a manufacturer manage to get nearly every BGA chip soldered correctly, whereas BGA repair for things such as the CPU socket is more like a 75/25 or a 50/50 at best?

[JoostinOnline]

I would assume it's because

1. Resoldering also involves removing it
2. Repair shops don't have multi-million dollar machinery to do it in mass production.

[porina]

When you have an assembly line manufacturing this on mass, you can set it up to place components very exactly.

 

If you're doing a manual rework, you're then having to do it yourself. You need to clean and prepare the surface where the component goes. Anything wrong there, you wont get good contact. Assuming you get that done and place it, you have to align it very accurately, and keep it there until the solder has cooled. There's just more scope for things to go wrong... I'm guessing temperature profile might be a contributing factor too, like it if cools too fast, you might get bad connections. If it cools unevenly, it could shift.

[iamdarkyoshi]

In manufacturing, they have dedicated stencil that the solder paste is dispensed through by machine, giving a very repeatable and even result.

 

The parts are placed by very expensive pick n place machines that scan each part to make sure it'll place it properly

 

When it comes to soldering, they go through a reflow oven which heats the whole board, not just the BGA part, which reduces thermal strains on the PCB.

 

The pads are also very clean when they're new, usually gold plated. Solder loves to stick to a nice clean surface of gold.

[Sauron]

19 minutes ago, JoostinOnline said:

I would assume it's because

1. Resoldering also involves removing it
2. Repair shops don't have multi-million dollar machinery to do it in mass production.

3. Repair shops don't have consistent access to known good replacement parts

[Unimportant]

Removing the chip comes with risks such as ripping a pad and trace if even a single solder ball has not fully melted. During production nothing has to be removed so those things can't happen.

 

Most of these parts also are not rated to stand the stress of soldering temperatures over multiple times, it's supposed to only handle that once.

 

There's also side effects of the thermal stress on the board, it only takes a slight bit of heat warping to possibly crack SMD MLCC and similar parts.

[Hackentosher]

Let's also not forget that most repair shops may not be as clean, introducing more contaminants which could cause damage.

[mariushm]

8 hours ago, hihihi8 said:

As titled, how does a manufacturer manage to get nearly every BGA chip soldered correctly, whereas BGA repair for things such as the CPU socket is more like a 75/25 or a 50/50 at best?

Because most often, it's not the poor soldering of the cpu that's the problem but rather something else - often when it does work it's just luck that by reballing the chip other things on the board get reheated and maybe bad solder connections become good again, or stuff like that.

 

Also, a  good professional doesn't reball the same chip, he/she replaces the reballed chip with a known working one.

 

But when manufacturing a card, all the parts are soldered professionally, in wave soldering machines or in high end machines that have very precise temperature controls (pre-heat, heating, soldering, cooling off etc.) and the boards are tested before they're shipping and if some soldering problems happen, most likely that board will be set aside so that the gpu chip would be soldered on refurbished or whatever boards sent to customers as warranty replacements.