Thanks guys. On my IRFP240 (TO-247AC) the metal does extend all the way to the edge of the package, but I see now why it isn't a big concern. I appreciate it, because ironically I spent about 40 minutes poring over the Digikey and Mouser catalogs for something that would work. Digikey carries those large rectangular TO-3 micas that I've used in the past on flatpacks, but they aren't stocked. grrr...
My order for the 4170s goes out today!
My order for the 4170s goes out today!
tiroth said:
Why not Digi-Key:
BER178-ND HEATPAD TO-247 .009" SP900
Seems stocked to me? Sure, not Aluminium Oxide but Bergquist SilPad SP900...
UrSv said:
I bought some of those thin heatpads, and when I tightened the device down against them, the package shorted against the heatsink. Maybe I got a bad batch of them (i ordered the black colored ones from digikey), but I don't trust them anymore. I feel secure, using them.
I used these:
BER131-ND -- Q3-104
I choose them because they were rated very high performance. I also wasted $25 on 50 of them... the 4170 cost me $30 for 100 of them.
--
Brian
Maybe you tightened them too much? I was using Sil-pads previously and they didn't present problems either. It's usually recommended to use only as little pressure as required. I'm using no more than a first 1/4 of the torque value on my cordless screwdriver.
Peter Daniel said:
That is quite possible, and I might consider trying them in the future again if I run out of the 4170s. I just feel more secure using the thicker ceramic devices.
Does anyone know about the difference between the physical properties of each?
--
Brian
It is true that working with those ceramic pads makes you feel completely safe and there's not even a sightest chance of creating a short.
The extra thickness of the pad may be advantegous, as the capacitance between device and heatsink is reduced. Also, the ceramic material is more brittle and it will provide less damping than the soft Sil-pad. In some cases it may be desirable. As to thermal conductivity, they are both very good.
The only drawback is that you have to use thermal grease with ceramic pads and with sil-pads, you don't.
The extra thickness of the pad may be advantegous, as the capacitance between device and heatsink is reduced. Also, the ceramic material is more brittle and it will provide less damping than the soft Sil-pad. In some cases it may be desirable. As to thermal conductivity, they are both very good.
The only drawback is that you have to use thermal grease with ceramic pads and with sil-pads, you don't.
Peter Daniel said:
The seperation is the best property in my mind, especially for p2p stuff where the extra clearance really helps. I also feel more secure using thermal grease with the pads also, even though it tends to make a mess.
Have you tried using any exotic thermal grease? I noticed that the computer overclocking crowds really love using expensive thermal grease and claim that the silver stuff works a lot better than the standard silicone stuff.
--
Brian
I know Digikey sells Silpads, I just didn't want them. Thanks for the tip on the "High performance" variant.
I read some reviews recently that showed extremely small differences between Arctic Silver and normal compound. Arctic Silver is also conductive under pressure and the manufacturer warned me not to use it when large potential differences are involved.
I read some reviews recently that showed extremely small differences between Arctic Silver and normal compound. Arctic Silver is also conductive under pressure and the manufacturer warned me not to use it when large potential differences are involved.
BrianGT said:
I've got some Arctic Silver 3 that I bought for my PC some time ago. Compared to "standard" thermal grease it makes a CPU run 5-7°C cooler (if my memory serves me well).Peter Daniel said:
You can find more info here: http://www.arcticsilver.com/
I think the AS3 cost me +-10€. I guess you could easily apply grease to over 60 pads if you don't waste to much, maybe more, who knows?
Devil_H@ck said:
The Arctic silver products are extremely good, and do provide much better heat transfer than normal silicon grease. Arctic Silver Ceramique is actually much better than AS3, and also significantly cheaper because of the fact that is uses aluminum oxide ceramic and a few other ingredients rather than the micronized silver in AS3. Arctic Silver 5 is better yet, but also quite expensive at up to $10 for a 3.5-oz. tube.
I had a problem shorting a TO-247 while using a silpad. The reason was that they were just barely large enough to cover the package. That is there was virtually no extra material around the margins. Thus, when I misaligned the pad and the device without realizing it, a small corner of the metal plate (collector) on the back of the device was exposed. I take care to watch that more carefully now and extrapolating from the experience use TO-247 size pades with To-220 and TO-220 size pads with TO-126. At least when I have the room. That ensures that the pad extends substantially beyond the edge of the device.
I also recommend Arctic Silver Ceramique as it is not electrically conductive, not all that hard to apply (unlike "high performance" grease available elsewhere) etc.
Petter
Petter
MSDS for BeO
Safety (MSDS) data for beryllium oxide
--------------------------------------------------------------------------------
General
Synonyms:
Molecular formula: BeO
CAS No: 1304-56-9
EINECS No: 215-133-1
Physical data
Appearance: solid
Melting point:
Boiling point: 3900 C
Vapour density:
Vapour pressure:
Density (g cm-3): 3.01
Flash point:
Explosion limits:
Autoignition temperature:
Water solubility:
Stability
Stable.
Toxicology
Extremely toxic by inhalation and ingestion. Typical LD50s for beryllium compounds are between 0.5 and 5 mg kg-1. Probable human carcinogen. Serious respiratory irritant. May be harmful by skin contact.
Toxicity data
(The meaning of any abbreviations which appear in this section is given here.)
RAT-IHL ACUTE 100 microg m-3
RBT-IHL CHRONIC 40-75 mg m-3
ORL-RAT LD50 (beryllium) 0.5 mg kg-1
Transport information
Personal protection
Use only under properly controlled conditions. Avoid breathing dust or powder. Use safety glasses, gloves, good ventilation. Treat as a probable carcinogen. Prepare a full risk assessment before starting work.
[Return to Physical & Theoretical Chemistry Lab. Safety home page.]
--------------------------------------------------------------------------------
This information was last updated on October 6, 2003. We have tried to make it as accurate and useful as possible, but can take no responsibility for its use, misuse, or accuracy. We have not verified this information, and cannot guarantee that it is up-to-date.
Safety (MSDS) data for beryllium oxide
--------------------------------------------------------------------------------
General
Synonyms:
Molecular formula: BeO
CAS No: 1304-56-9
EINECS No: 215-133-1
Physical data
Appearance: solid
Melting point:
Boiling point: 3900 C
Vapour density:
Vapour pressure:
Density (g cm-3): 3.01
Flash point:
Explosion limits:
Autoignition temperature:
Water solubility:
Stability
Stable.
Toxicology
Extremely toxic by inhalation and ingestion. Typical LD50s for beryllium compounds are between 0.5 and 5 mg kg-1. Probable human carcinogen. Serious respiratory irritant. May be harmful by skin contact.
Toxicity data
(The meaning of any abbreviations which appear in this section is given here.)
RAT-IHL ACUTE 100 microg m-3
RBT-IHL CHRONIC 40-75 mg m-3
ORL-RAT LD50 (beryllium) 0.5 mg kg-1
Transport information
Personal protection
Use only under properly controlled conditions. Avoid breathing dust or powder. Use safety glasses, gloves, good ventilation. Treat as a probable carcinogen. Prepare a full risk assessment before starting work.
[Return to Physical & Theoretical Chemistry Lab. Safety home page.]
--------------------------------------------------------------------------------
This information was last updated on October 6, 2003. We have tried to make it as accurate and useful as possible, but can take no responsibility for its use, misuse, or accuracy. We have not verified this information, and cannot guarantee that it is up-to-date.
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