Inductor dissipating 2.8W with thermal reliefs - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: December 03, 2022, 12:14:01 am
content: Hi,The inductor (ringed) on this PCB, dissipates 2.8W. Its a vishay IHLP6767-GZ-01 (5.6uH).Its the inductor for a boost, 5vin 24vout, 3A75 out, 350kHz.PCB is 4 layer, 1 oz copper all layers.All layers underneath the inductor are GND, and dont connect to this inductor.1....Do you believe we could do away with the thermal reliefs here?IHLP6767-GZ-01 (5.6uH).https://www.vishay.com/docs/34000/ihlp-6767gz-01.pdf

author: Gyro
author_rank: Super Contributor
timestamp: December 03, 2022, 02:10:47 pm
content: I don't think belief comes into it - you either work it out or you don't bother!

author: Faringdon
author_rank: Super Contributor
timestamp: December 03, 2022, 03:32:14 pm
content: Thanks, we appreciate we can hand solder it even if there are no thermal reliefs, but we wonder if the SMD soldering machine will be able to?

author: asmi
author_rank: Super Contributor
timestamp: December 03, 2022, 05:06:03 pm
content: During reflow the entire structure of pcb is brought up to soldering temperature, so presence of reliefs doesn't change anything.

author: Faringdon
author_rank: Super Contributor
timestamp: December 03, 2022, 05:46:07 pm
content: QuoteThnaks, though that makes us wonder why people ever use thermal reliefs?

author: Gyro
author_rank: Super Contributor
timestamp: December 03, 2022, 07:03:47 pm
content: Components have different thermal masses and heat and cool at different rates under the reflow profile.

author: Faringdon
author_rank: Super Contributor
timestamp: December 03, 2022, 09:32:58 pm
content: Thanks, so the thermal releif is so that all can get up to temp in the alloted time?....in other words, thermal reliefs are always needed?But come to think ot it...ive done SMD LED boards with no thermal reliefs and the PCB assembler said it was fine, and soldered the boards up nicely for us....presumbaly they just had to do a few dummy runs to get the temperature and time profiles right?....so in other words....we do NOT actually need thermal reliefs...but must just tell the PCB assembler that we dont have them?Then they can give extra "deep-fry" to the boards in the solder bath so that the non thermal relived inductor can get soldered?

author: wraper
author_rank: Unknown
timestamp: December 03, 2022, 09:39:05 pm
content: Thermal reliefs for SMD are needed so parts do not tombstone during reflow. However it does not happen with larger and heavier parts like power inductors. Above 0805 size tombstoning is rarely an issue. So there is no need to use them.

author: Faringdon
author_rank: Super Contributor
timestamp: December 11, 2022, 02:33:30 pm
content: Thanks for all these great replies.....it seems to me now that thermal reliefs are not needed for the inductor concerned...but if no thermal reliefs are used, then the pcb assembler will have to heat the board for longer to get everything up to temperature, which could potentially damage or weaken some other components.?It does seem fair to say that if no thermal reliefs are used with a board with a big inductor as above, then the pcb assembler will need to be told about this?

author: asmi
author_rank: Super Contributor
timestamp: December 12, 2022, 03:35:39 pm
content: Quote from: Faringdon on December 11, 2022, 02:33:30 pmWhat makes you think this?

author: jonpaul
author_rank: Super Contributor
timestamp: December 17, 2022, 01:29:50 am
content: FTTS againpoor design, excess inductor dissipatingreview losses, inductor choice and just fix itj