What is a BGA?
The Ball Grid Array, (BGA), uses a different approach to the connections to that used for more conventional surface mount connections. Other packages such as the quad flat pack, QFP, used the sides of the package for the connections. This meant that there was limited space for the pins which had to be spaced very closely and made much smaller to provide the required level of connectivity. The Ball Grid Array, BGA, uses the underside of the package, where there is a considerable area for the connections.
The pins are placed in a grid pattern (hence the name Ball Grid Array) on the under-surface of the chip carrier. Also rather than having pins to provide the connectivity, pads with balls of solder are used as the method of connection. On the printed circuit board, PCB, onto which the BGA device is to be fitted there is a matching set of copper pads to provide the required connectivity.
Apart from the improvement in connectivity, BGAs have other advantages. They offer a lower thermal resistance between the silicon chip itself than quad flat pack devices. This allows heat generated by the integrated circuit inside the package to be conducted out of the device onto the PCB faster and more effectively. In this way it is possible for BGA devices to generate more heat without the need for special cooling measures.
In addition to this the fact that the conductors are on the underside of the chip carrier means that the leads within the chip are shorter. Accordingly unwanted lead inductance levels are lower, and in this way, Ball Grid Array devices are able to offer a higher level of performance than their QFP counterparts.
BGA chips soldering and replacement
Many people are afraid to try to solder BGA ICs and think, that this is very complicated process and require lot of expensive tools.
Indeed if you do mass production you need expensive and precise machines to place and reflow the boards which cost a lot of money.
If you have to assembly and repair small quantity of boards though you can do it with low cost equipment as well.
Sure you may broke some ICs and boards until you learn how to do this properly, but this should not discourage you.
In this tutorial we will show you how A20-OLinuXino with burned processor is repaired using only few low cost tools:
- hot air desoldering tool
- soldering iron
- solder wick
- tacky flux
- isopropile alcohol
all above cost total less than EUR 200
Step 1 – hold the IC with twizzers and move the hot air handle above the IC trying to heat it equally
Step 2 – using solder wick remove the excessive solder on the BGA pads, not everything will be removed
Step 3 – apply flux and repeat step 3 until make pads completely even with no solder blobs
Step 4 – clean with isopropile alcohol
Step 5 – apply tacky flux
Step 6 – position the BGA chip on the pads (in our designs we place 4 small pads in the BGA corners so when you place the IC the corner of the ICs lay on these registration pads)
Step 7 – heat the BGA with the hot air to 250 C and keep it hot above 250 C for about 30 seconds.
Lead Free Solder melting point is 225 C, to solder the IC reliable it should be heated to 250 C and then hold at this temperature for 30 seconds.
You can do some experiments to learn when the IC is heated to this temperature and how long it takes to heat up by using damaged BGA chip – put thermocouple on bottom of it and place the IC on damaged board as you have to measure the temperature of the balls not on top of the IC then start heating and monitor the temperature, you will see after what time, when you move the hot air gun the temperature reach 250 C, note that the distance between the hot air gun and IC changes the temperature significant, also the complete IC should be heated and you have to move the hot air with circulating moves not to keep it at one spot only.
Once you do the measurements you will know what amount of time you have to heat the IC and at what distance and you can try with real chip.
When BGA balls melt down they “collapse” and the BGA sinks down a little bit, with the time you will get experience and will notice this collapse to be sure when the BGA balls are really soldered.
You can check your soldering results with magnifying glass looking at the BGA sides.