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The chip that I want to attach a heat sink is a WiFi chip Ralink RT3070 and its separate RF amp chip YP243433 both have 85C Tjunc. The amp chip barely gets hot. The main chip gets hot but still can be touched (maybe 50-55C). Will the RF performance affected by heat sink? There's no RF can/lid/shield on both chip.

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  • \$\begingroup\$ If you can leave your finger on it, what makes you think the heat is affecting performance or safety enough to warrant a heatsink? And I'm going to say yes you can place a heatsink without affecting rf performance. \$\endgroup\$
    – Passerby
    Oct 7 '17 at 4:49
  • \$\begingroup\$ @Passerby I'm using a higher TX power more than its default 20dBm, currently at 33dBm \$\endgroup\$
    – JFetz2191
    Oct 7 '17 at 4:58
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The 60-page data sheet is available for download. See the link "Download PDF File" near the bottom of this web page: http://www.datasheet4u.com/datasheet/R/T/3/RT3070_Ralink.pdf.html

Interesting, on page 7 of the data file: while it mentions nothing about the use of a heatsink, it does clarify that the AMBIENT temperature in which the chip should be used is 85 degrees C. However it states that the maximum case temperature for operation is 125 degrees C. You could instantly burn your finger by touching it and it could still be working within thermal spec. I know this doesn't answer your question, but perhaps it does, albeit obliquely.

Another interesting part of the data sheet, still page 7, says you must bake the chip if you unwrap it from its package and then do not install it within 168 hours. The baking regime is 8 hours at 125 degrees C.

All this is highly suggestive that one does not need a heat sink for this obviously thermally rugged chip.

I did retire before I got into this general level of chip, but having learned over years of personal experience in reading - and trusting - data sheets, I would suggest using this chip without a heatsink if indeed you have found that you can rest your finger on it in use without burning your finger.

I hope this helps although I am aware I still have not directly answered your question.

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  • \$\begingroup\$ Well, the board is fairly thick maybe that'll dissipate some heat + this module is inside an panel type antenna that can be installed on roofs. Anyway thanks, I got only basic understanding on datasheet values. Cheers \$\endgroup\$
    – JFetz2191
    Oct 7 '17 at 6:00
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    \$\begingroup\$ Well yes, it is known that suppliers/designers of circuit boards have a range of copper thicknesses coated to the board to choose from at the concept/design stage. It goes without saying that any chip which is desired to give a little heatsinking to via its leadout pins, will have a board provided with sufficient copper thickness to do its part to help dissipate internal heat carried out through each pin. No, it's not much of a heatsink, I agree. Yes, it's done because it is way better than not considering heat at all at the board design stage, so why wouldn't anyone do it? \$\endgroup\$
    – Stan H
    Oct 7 '17 at 6:27
  • \$\begingroup\$ Standard CU foil thickness provides 70 degree Centigrade thermal resistance for heat flow, per square of copper. In a 3*3 grid, the heat injected into the middle square, the surrounding 8 squares provide 70/8 = 9 degree Centigrade thermal resistance. The next surrounding grid, of sise 3X bigger squares, adds another 9 degree thermal Resistance. Is 18 degree thermal resistance too large? Use thicker copper, use multiple planes, use the chassis of the system/ \$\endgroup\$ Oct 7 '17 at 15:57

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