what is required to solder something without thermal stress - Page 1
Forum section: electronics / projects

author: sarepairman2
author_rank: Frequent Contributor
timestamp: September 20, 2015, 05:35:33 am
content: will a heat laser + thermal paste do it? rather then like, trying to say, put heat sinks on MSOP pins while yoou solder them.obviously reflow will just fuck it up. for SMD stuff, not socketed.high power thin ultrasonic horn?

author: Rerouter
author_rank: Super Contributor
timestamp: September 20, 2015, 05:40:33 am
content: Care to better describe the issue? I reguarly solder MSOP via hot air with no issue, laser will still make its way into any chip that small as the mass of the leg is so small compared to the thermal mass of the PCB, justy less heat into the package, however unless you get every pin at the exact same moment you will introduce mechanical stress on the package,

author: sarepairman2
author_rank: Frequent Contributor
timestamp: September 20, 2015, 05:54:42 am
content: that seems doable for smaller packages. beam splitter cascadei am looking into volt nuttery with smd devices, thermomechanical drift just shits all over everything lol

author: Rerouter
author_rank: Super Contributor
timestamp: September 20, 2015, 06:25:39 am
content: Ok, another way may have to play into abusing the mechanical properties of solder, If your connections are of such a high impedance that solder cold flowing will not be an issue, you could get away with finding a blend of solder with a much lower melting point, e.g. chipquick melts at 52 degrees, so varying how much is added with regular solder in a blend will likely very the melting point,Doing this you could say heat the pcb from the rear so that the pads are at something like 115C, where your blend will melt, and then set the chip in place, allowing it to air dry back down, the thermo stress will be reduced due to only 1/3rd heating, and the solder blend even if weaker will be softer imparting even less stress as it cools, just remeber to use flux as you really want a wet joint for this

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: September 20, 2015, 06:47:54 am
content: I have no experience with it but what about electrically conductive adhesive?

author: IanB
author_rank: Super Contributor
timestamp: September 20, 2015, 07:17:58 am
content: Solder will not work unless the metal surfaces being soldered reach a temperature higher than the melting point of the solder. So the pins of your package must reach this temperature.Now you need to define what you mean by "thermal stress". The normal meaning of this word is damage caused by differential expansion when one part of a device is hotter and another is cooler with a significant temperature gradient between them. One mitigation for thermal stress is to keep the heat localized and the exposure time short. For example, by spot welding. In a soldering context, use a hot iron with a high thermal mass and keep the soldering time as short as possible.Another mitigation for thermal stress is to preheat the board and parts before soldering so they do not experience big temperature differences, or to use a suitable temperature profile in a reflow oven so that everything warms up equally and big temperature gradients do not occur.Maybe, however, you mean "temperature damage"? This would be where high temperatures themselves cause damage. This might rule out ovens or hot air. However, a high thermal mass iron with a short soldering time could still be an option. If even this level of heating is undesirable, then an IC socket could be used (there are sockets for some kinds of SMT packages).

author: SeanB
author_rank: Super Contributor
timestamp: September 20, 2015, 08:07:20 am
content: Silver loaded epoxy will work, just be very aware that the resistance will be higher, and you will need to have both the substrate and the chip pin be both clean and oxide free when applying the epoxy. You will also need to apply a conformal coat afterwards to prevent the silver in the epoxy from degrading with corrosion and time. Just make sure the coating is compatible with the epoxy, easiest if both are made using the same base components from the same manufacturer.

author: John Coloccia
author_rank: Super Contributor
timestamp: September 20, 2015, 08:49:10 am
content: Isn't your package designed to be soldered? In the datasheet there will be a couple of lines that tell you precisely what it can take in terms of heat. What's the problem you're trying to solve? I've never used heat sinks except occasionally on through hole germanium parts, because they truly are quite sensitive to excess heat.

author: eneuro
author_rank: Super Contributor
timestamp: September 20, 2015, 09:24:39 am
content: Quote from: IanB on September 20, 2015, 07:17:58 amI want test induction heating in my PnP assembly head to try move such induction heater over element (eg. 10mm radius of high frequency dtrong magnetic field) induce Eddy curents in solder (paste) and heat to temperature it melts-we could control this process perfrctly using thermal imaging camera, but with massive GPU processing of visual camera image at good light condition, we could also detect that solder (paste) changed its surface to shiny reflective, I guess.Anyway, for heatsink soldering using brazing method, I'm testing spot welder with two metals of lower electrical conductivity and solder (paste) inserted between them into small displacement, solder should melt and with the help ofwiki: surface tensionmelted to high temperature, but very fast, since hundreds of amps of spot welder current will quickly heat up solder (paste) and surfaces it touches, small gap betweenwiki: brazingmetals will be filled with shiny solder (paste) since whole process can be very quick, however it might be a little bit tricky to controll it.Below experiment with... vapourized copper strand wire (2.5mm2) using spot welder high current, so no problem to melt ICs pins, heatsinks etc

author: DanielS
author_rank: Frequent Contributor
timestamp: September 20, 2015, 01:02:07 pm
content: Quote from: eneuro on September 20, 2015, 09:24:39 amWhat about the eddy currents and voltages induced in and around the parts being soldered themselves?If I was worried about mechanical stress affecting the precision of a part, I would put slots around those critical pins to give them plenty of flex.

author: eneuro
author_rank: Super Contributor
timestamp: September 20, 2015, 01:28:17 pm
content: Quote from: DanielS on September 20, 2015, 01:02:07 pmhttps://en.wikipedia.org/wiki/Soldering#Induction_solderingQuoteI've almost completed ZVS driver (similar to this onehttp://www.rmcybernetics.com/projects/DIY_Devices/diy-induction-heater.htmbut improoved myself ) used in DIY induction heaters and it looks like not too high input voltage needed to heat screw driver, so while there is a few turns splited coil in those heaters, so induced voltage is shorted circuit by heated (solder) resistance and probably not too high induced volatges present, but I didn't tested it yet.I will make experiments with induction heating next week and we'll see how this simple ZVS driver performs at up to quite safe 36V input power

author: amyk
author_rank: Super Contributor
timestamp: September 20, 2015, 01:52:47 pm
content: Quote from: sarepairman2 on September 20, 2015, 05:54:42 amIf you mean things like voltage references, those are calibratedafterbeing mounted, so any thermally induced change has no effect.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: September 20, 2015, 04:25:58 pm
content: Quote from: eneuro on September 20, 2015, 09:24:39 amif i had any money i would hire you this is the kind of ideas i like

author: sarepairman2
author_rank: Frequent Contributor
timestamp: September 20, 2015, 04:26:51 pm
content: Quote from: amyk on September 20, 2015, 01:52:47 pmim not an expert but i am pretty sure that after you fuck with a package it takes a long time for everything to equalize, i heard like months for some foil resistors etc

author: nitro2k01
author_rank: Frequent Contributor
timestamp: September 22, 2015, 04:46:33 am
content: Which actual chip(s) are you using? What is circuit doing?