EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: akis on April 26, 2016, 02:13:48 pm
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I have watched some youtube videos showing insertions and removal of various components/ICs using hot air guns, for example you have an IC with 200 pins on its underside and you solder it in place with hot air, which means you have to raise the temperature of the whole area to 260C or more, and that includes the whole component(s), not just the pins and not just one pin at a time.
So for example I have soldered some MOSFETs onto the PCB, where I also soldered their drain (the metal backside) and to do that the whole area has to reach 260C, but the absolute max ratings specify 300C for 10 seconds 1.6mm from case.
Under a hot air gun this component, and others, would reach 260C (or more) on its case, the whole thing.
The explanation I am guessing is that components are much more resilient and can withstand at least 260 C for many seconds, but am I understanding it correctly?
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I have watched some youtube videos showing insertions and removal of various components/ICs using hot air guns, for example you have an IC with 200 pins on its underside and you solder it in place with hot air, which means you have to raise the temperature of the whole area to 260C or more, and that includes the whole component(s), not just the pins and not just one pin at a time.
So for example I have soldered some MOSFETs onto the PCB, where I also soldered their drain (the metal backside) and to do that the whole area has to reach 260C, but the absolute max ratings specify 300C for 10 seconds 1.6mm from case.
Under a hot air gun this component, and others, would reach 260C (or more) on its case, the whole thing.
The explanation I am guessing is that components are much more resilient and can withstand at least 260 C for many seconds, but am I understanding it correctly?
Yes, that's been my understanding too.
A study of reflow temp profiles might assist with better understanding
https://www.google.co.nz/search?q=soldering+reflow+profile&rlz=1C1ASUM_enNZ497NZ497&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjW7cDylq3MAhVBKJQKHeh0Ck4QsAQIGg (https://www.google.co.nz/search?q=soldering+reflow+profile&rlz=1C1ASUM_enNZ497NZ497&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjW7cDylq3MAhVBKJQKHeh0Ck4QsAQIGg)
I'd add that component manufacturers max temp ratings will be for a guaranteed 100% survivability and to help the hobbyist or repair technician it's a good idea to have some low temp solder and paste on hand for when you judge you might exceed manufacturers temp ratings.
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I believe an underboard infrared heater is good for this type of thing. I don't have one but I'm noticing that old coffee maker in the back cupboard has a heatplate perhaps being liberated to provide some assistance? It can't hurt if its kept relatively low temp surely? ;)
ETA: I also find old lead solder boards are just a dream to rework with hot air - its like a magic wand. All this lead free crap and the glued down chips really cramp my style!
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The thing is called a preheater and you can get these hotplates for about $100 delivered:
http://www.aliexpress.com/item/Free-shipping-110-220V-850W-YOUYUE-946C-200X200mm-Digital-Thermostat-Platform-heating-plate-preheating-station/32438533886.html (http://www.aliexpress.com/item/Free-shipping-110-220V-850W-YOUYUE-946C-200X200mm-Digital-Thermostat-Platform-heating-plate-preheating-station/32438533886.html)
You probably wouldn't want to do a 300+ pin BGA with this, but it helps to bring up the board up to temperature and then you use hot air to "push it over the edge" (the soldering peak in the reflow profile).
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You're definitely describing a preheater (i.e. hot air or IR).
And since this need to be beneath the board, you'll need some kind of fixture to hold it over the preheater while it ramps up. Perhaps during soldering as well.
FWIW they don't see a lot of use vs. an iron or even hot air station (i.e. not a lot of layers, and small - medium package size IC's), so unless you'll be using the devil out of it, you don't need to spend Hakko, Weller, Ersa, ... kind of money. ;)
A couple of photos & links below:
Quick 853 (http://www.aliexpress.com/item/QUICK-853-ESD-Anti-static-Hot-air-preheating-station/32215094746.html?spm=2114.01010208.3.1.lCE1QM&ws_ab_test=searchweb201556_10,searchweb201602_3_10017_10005_10006_10034_10021_507_10022_10009_10020_10008_10018_10019,searchweb201603_7&btsid=ea09a14b-813c-4257-807b-9bffcf94d3a5)
(http://i.imgur.com/VjkryM0.jpg)
Quick 854 (http://www.ams-electronics.co.uk/shop/hot-plates/quick-854-esd-pre-heater-plate/)
(http://i.imgur.com/z2NY9F5.jpg)
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I wonder if anyone has run tests "before" and "after", eg testing a MOSFET for Rdson or a power transistor for beta and then heating the whole component to 300C for 10 seconds, then letting it cool down and then take the same measurements again.
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I wonder if anyone has run tests "before" and "after", eg testing a MOSFET for Rdson or a power transistor for beta and then heating the whole component to 300C for 10 seconds, then letting it cool down and then take the same measurements again.
You expect there to be a change? Most parts today are designed to be wave or reflow soldered where they are sitting there at temperature often for longer than 10 seconds - just look at the recommended temperature profiles in the datasheet.
It would be an interesting test, but I think you will not find much. Modern components are surprisingly resilient to temperature and will survive quite a bit of beating, even far beyond the recommended datasheet values (not that I recommend doing that).
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You're definitely describing a preheater (i.e. hot air or IR).
Not having used one of these myself - is there an advantage in using these over the hotplate type I have posted earlier? The hotplate can be used also for reflow soldering, which a hot air preheater can't. On the other hand, the hotplate doesn't work if you have the board populated from both sides already.
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You're definitely describing a preheater (i.e. hot air or IR).
Not having used one of these myself - is there an advantage in using these over the hotplate type I have posted earlier? The hotplate can be used also for reflow soldering, which a hot air preheater can't. On the other hand, the hotplate doesn't work if you have the board populated from both sides already.
Have wanted to know the various benefits from peoples experience on preheating this for quite some time but there didn't seem to be many replies knowledgeable on the subject (see the link with my questions at the bottom of my post).
Regarding double sided PCBs you can still preheat the underside, you just need to consider plastics and the tolerances of components. Underside preheating is not at full temp and is only performed to assist the reflow on top and prevent other damage like bringing up the temp of the pcb to avoid warping.
The other thing is if the components on the underside do get reflowed for a short amount of time surface tension of the solder can hold them in place. If you were to use aggressive heat and airflow from the underside that is going to be a problem.
As mentioned lots of information from the manufacturers on temp profiles and component tolerances on the web because they are used in production. Plenty of videos on youtube on this as well.
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Not having used one of these myself - is there an advantage in using these over the hotplate type I have posted earlier? The hotplate can be used also for reflow soldering, which a hot air preheater can't. On the other hand, the hotplate doesn't work if you have the board populated from both sides already.
- Heats up quickly.
- Very flexible regarding placement & board size when the board is mounted in a separate fixture (i.e. selective rework on larger boards).
- Max temp is typically 250C - 300C, so they're a bit less likely to cause damage to the board or components. This can also be a disadvantage if you want to actually solder with it, as it will require a second heat source (not designed to solder on its own).
- They're typically cheaper IME (I only paid ~$55 for mine IIRC).
The hot air plate type in the photo seems to have about vanished lately, so all this ^ may have become moot (Hakko FR-830 is still available, but costs ~$350). :-//
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For the plate type pre-heaters, I assume one is to put the board directly on the plate? (It seems obvious that's the case, but I want to double-check.)
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For the plate type pre-heaters, I assume one is to put the board directly on the plate? (It seems obvious that's the case, but I want to double-check.)
Only if the surface is sheet metal or flat ceramic (no holes or vents, or non-flat surfaces).
If its expanded metal (holes/vents as are in the photo of the 854), I've always seen them used with a board fixture of some sort, just as you would with hot air.