BGA chip replacement, when board is difficult to heat - Page 1
Forum section: electronics / repair

author: peter-h
author_rank: Super Contributor
timestamp: January 11, 2024, 07:20:01 am
content: I've had to replace some of these old gyro chipsand there are issues:- no access to the back of the board (e.g. for a hotplate or hot air)- there are components on the back- the device has unleaded solder balls whose melting point is not far below the 260C max soldering tempI found it basically impossible to melt the balls without getting the whole thing extremely hot. One of the $50 chips was probably damaged. I found a way by removing these balls (with a soldering iron) and replace them with 60/40 solder "balls", which are much smaller than original but are easily formed by running an iron over the pads, with plenty of flux applied.I have two hot air guns. One is 260C (measured actual airflow temp) and the other is a chinese adjustable one.Is there some better way?

author: DavidAlfa
author_rank: Super Contributor
timestamp: January 12, 2024, 03:38:37 am
content: Crank the temp up to 350, no way you're removing it with 260C!Why can't you shot hot air at the back?It's in a corner, should be pretty easy, unlike when it's in the middle of a beefy board sucking all the heat.All parts in that small pcb will melt, also those at the back, no problem unless you shake the board.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 12, 2024, 09:24:02 am
content: Try with a preheater underneath, or a halogen lamp above (ideally an IR lamp, but a simple halogen spot placed close enough should work, you may want to use sunglasses) above if the back of the board is part of a bigger device.Use the preheater to heat the PCB at 100-150*C or so (but less than the melting temperature of the solder), then use the hot air station to pump up a little more heat upon the chip to replace only. If you have Kapton tape, stick it around the chip to replace, in order to form a window such that the hot air will fall on the chip to replace mostly, while protecting the surrounding parts against the extra heat.

author: wraper
author_rank: Unknown
timestamp: January 12, 2024, 09:33:32 am
content: Quote from: peter-h on January 11, 2024, 07:20:01 amIsn't it apparent to you that PCB will never reach hot air temperature? Especially when heating from just one side with no bottom preheater. As long as hot air gun temperature is accurate (many Chinese stations run hotter that set), you rarely want less than 350oC with lead-free with exception when soldering plastic connectors, but then you also want a preheater.

author: selcuk
author_rank: Frequent Contributor
timestamp: January 12, 2024, 10:15:16 am
content: I usually fold a thin sheet of copper around the IC to heat from the top and protect the other components. I fold it as a rectangular box open from top and bottom. Exact size and shape depends on the chip and surrounding components. I solder its ends to make the shape permanent.This is the commercial version:

author: peter-h
author_rank: Super Contributor
timestamp: January 12, 2024, 10:18:37 am
content: WOW where can you get that kit?I don't have access to the back of the board.On a positive note I have managed to replace four of these chips so far, using the method of replacing the balls with (much smaller) balls of 60/40 solder and then heating the chip with a 260C airflow until it can be seen to "sit down".

author: selcuk
author_rank: Frequent Contributor
timestamp: January 12, 2024, 10:37:26 am
content: I believe it is bundled with JBC hot air stations. I don't know whether other brands have this kit.

author: wraper
author_rank: Unknown
timestamp: January 12, 2024, 11:33:01 am
content: Quote from: peter-h on January 12, 2024, 10:18:37 amThat kit is overpricedhttps://eleshop.eu/jbc-esht-extractor-desk-for-hot-air-soldering-stations.html, has very limited use as it will fit barely anything unless IC is absolutely free of surrounding passives and barely any professional uses anything like this. This is likely why nobody besides JBC makes this. "Protecting surrounding components" is actually not needed in 95%+ of cases and heating only one spot instead of all board causes PCB warping actually. That's why large BGA replacement on motherboards requires very large preheater that can heat the large motherboard entirely.