Reflow soldering in kitchen with ceramic hub

[tatus1969]

does your math take into account that I don't eat solder paste like fish?

You're missing out, I like to spread it on crackers 

If you don't spread it too thick, then it should be not much worse than a fish meal I just googled that out of curiosity, and read that the EU plans to raise the limit for mercury in predator fish from 1mg to 2mg per kg. What? 2mg?

[JuKu]

Solder starts melting at 1:09, and I remove the boards at 2:31, is that too short?

The paste manufacturer has the recommended profile for their paste, but yes, that is short.

A typical profile is slow heating (<2C/s) to 150C, so this alone should take well over a minute. At that temperature, the chemicals in the paste activate. Then, you let those chemicals do their work for 1 to 3 minutes. This is called dwell or soaking time. For this, you really want to look at the paste data sheet, as there is a largish variation on best time. You want the chemicals to have done their job in getting the solder to stick to parts, but you want the flux still be there. Then the temperature is raised so that solder melts. It is not enough that the solder melts, the flux and other chemicals need some time for best results; typical reflow time recommendation is 60 to 90 seconds but again, see your paste data sheet. And finally, the boards should cool with a controlled rate as well, 6C/s max.

Of course, this is for industrial grade reliability, where one failed joint in a million is poor quality. Prototype builders and hobbyists can't always do things by the book and it is ok; for us it is fine to push parts in place manually, fix the odd tombstone or cold joint. A real factory will do it as above.

[tatus1969]

Solder starts melting at 1:09, and I remove the boards at 2:31, is that too short?

The paste manufacturer has the recommended profile for their paste, but yes, that is short.

A typical profile is slow heating (<2C/s) to 150C, so this alone should take well over a minute. At that temperature, the chemicals in the paste activate. Then, you let those chemicals do their work for 1 to 3 minutes. This is called dwell or soaking time. For this, you really want to look at the paste data sheet, as there is a largish variation on best time. You want the chemicals to have done their job in getting the solder to stick to parts, but you want the flux still be there. Then the temperature is raised so that solder melts. It is not enough that the solder melts, the flux and other chemicals need some time for best results; typical reflow time recommendation is 60 to 90 seconds but again, see your paste data sheet. And finally, the boards should cool with a controlled rate as well, 6C/s max.

Of course, this is for industrial grade reliability, where one failed joint in a million is poor quality. Prototype builders and hobbyists can't always do things by the book and it is ok; for us it is fine to push parts in place manually, fix the odd tombstone or cold joint. A real factory will do it as above.

The video doesn't show the preheat and soak phases that went before this. I wanted to keep it short and cut that part, maybe not such a good idea in the end.

[JuKu]

Ok, gave a wrong idea what happened.

[KL27x]

The preheat and soak phases are not complete BS, but... it has more to do with the board and components than the paste. On a small board with small components, you can get a proper "reflow" much faster than the "recommended profile," without overheating the board. Proper cooling is probably important, but not so much on smaller boards like these.

To illustrate:

typical reflow time recommendation is 60 to 90 seconds

I promise no one in their right mind is going to keep a joint flowing for 60 seconds when using an iron or a hot air station, no matter what paste/solder they may use. The reason this is the recommended time is to make sure all the parts reach flow temp before the ramp down begins.

[SeanB]

does your math take into account that I don't eat solder paste like fish?

You're missing out, I like to spread it on crackers 

If you don't spread it too thick, then it should be not much worse than a fish meal I just googled that out of curiosity, and read that the EU plans to raise the limit for mercury in predator fish from 1mg to 2mg per kg. What? 2mg?

2mg is about the mercury dose of a CFL lamp, which might have a life of around 2 years before going out in the waste stream, and most likely being broken in the process as well.

[tatus1969]

does your math take into account that I don't eat solder paste like fish?

You're missing out, I like to spread it on crackers 

If you don't spread it too thick, then it should be not much worse than a fish meal I just googled that out of curiosity, and read that the EU plans to raise the limit for mercury in predator fish from 1mg to 2mg per kg. What? 2mg?

2mg is about the mercury dose of a CFL lamp, which might have a life of around 2 years before going out in the waste stream, and most likely being broken in the process as well.

That comparison shows how ridiculous this limit value is. They allow fish for sale that has the same amount of mercury per kilo as a CFL lamp, which they highly recommend to be replaced by LEDs because of their health risk.

[SeanB]

The LED chips also contain large amounts of Arsenic as well in the dies, and that is not shown on the package.

[james_s]

True, although the arsenic in LEDs is a lot less likely to get out than mercury in a CCFL.

[DigitalDeath]

That was a cool hack. Thanks for posting it and for the post nannies please let a guy enjoy his passion without that much criticizing. It was a just cool thing he felt sharing.

[tggzzz]

My technique is:

• small saucepan with a glass lid; reduces chance of splattering and might allow a little heating from the top
• thin layer of sand in saucepan; spreads heat avoiding hotspots and enables more control of temperature profile
• gas ring, not electric hob

The only thing that doesn't allow is a "rapid" cooloff as shown in the temperature profile. That can be ameliorated by lifting the PCB out when solder has reflowed

[tatus1969]

My technique is:

• small saucepan with a glass lid; reduces chance of splattering and might allow a little heating from the top
• thin layer of sand in saucepan; spreads heat avoiding hotspots and enables more control of temperature profile
• gas ring, not electric hob

The only thing that doesn't allow is a "rapid" cooloff as shown in the temperature profile. That can be ameliorated by lifting the PCB out when solder has reflowed

Sounds interesting... I wonder how homogenous the heating would be with a gas ring.

[tggzzz]

My technique is:

• small saucepan with a glass lid; reduces chance of splattering and might allow a little heating from the top
• thin layer of sand in saucepan; spreads heat avoiding hotspots and enables more control of temperature profile
• gas ring, not electric hob

The only thing that doesn't allow is a "rapid" cooloff as shown in the temperature profile. That can be ameliorated by lifting the PCB out when solder has reflowed

Sounds interesting... I wonder how homogenous the heating would be with a gas ring.

That question is equally valid for an electric hob; the construction details will matter. My (very cheap) saucepan has a relatively thick base, which will spread the heat. The sand, or rather the air in between the sand grains, will also spread the heat. I presume that would also be the case if you spread sand directly on your electric hob. Why not try it with a sacrificial/scrap board (no components) and see? (And let us know the results!)

As far as I can see, it is even: 0603 sized components anywhere on a 5cm*5cm board start to reflow more or less simultaneously. Larger components may take a little longer, but that is due to their thermal mass, not uneven heating.

I have not seen any scorching on boards' undersides. A few grains of sand lightly stick to the underside, and are simply brushed off when cool.

If I wanted to try double-sided boards, I would experiment with mounting spacers on the board and putting it in the saucepan, optionally with less sand.

[tatus1969]

My (very cheap) saucepan has a relatively thick base, which will spread the heat.

That does certainly help, maybe comparable to the thick glass top of my hub.

The sand, or rather the air in between the sand grains, will also spread the heat.

I don't need any thermal conductor, because the glass top is naturally perfectly flat.

Why not try it with a sacrificial/scrap board (no components) and see? (And let us know the results!)

I will make a measurement with my IR thermometer and see how even the heat is spread, and how close I can come to something that deserves calling it reflow profile. I am already thinking of a dedicated hub with temperature sensor and triac controller

[tggzzz]

My (very cheap) saucepan has a relatively thick base, which will spread the heat.

That does certainly help, maybe comparable to the thick glass top of my hub.

The sand, or rather the air in between the sand grains, will also spread the heat.

I don't need any thermal conductor, because the glass top is naturally perfectly flat.

But is the PCB perfectly flat?

The sand also helps to slow down heat transfer and thus make temperature more controllable. I would expect that to be more beneficial on an electric hob which, in my limited experience, are less easy to control than gas hobs. Obviously there is a tradeoff between speed, control, and profile - experiments required

Why not try it with a sacrificial/scrap board (no components) and see? (And let us know the results!)

I will make a measurement with my IR thermometer and see how even the heat is spread, and how close I can come to something that deserves calling it reflow profile. I am already thinking of a dedicated hub with temperature sensor and triac controller

I find that I am a satisfactory heat controller

[KL27x]

in my limited experience, are less easy to control than gas hobs

A gas burner, you just turn to the size flame you want. The glass (halogen bulb?) hob in my kitchen appears to have thermostatic control. It turns on/off as needed, all by itself. If you turn it on without a load, for instance, it will spend a lot of the time totally off. Large enough load, and it will be 100% duty cycle. And it can be anywhere in between. And no, it's not very fine.... the hysteresis/oscillations are quite lengthy.

[cdev]

Couldn't the current/voltage being induced in the nearby boards conductors potentially damage something?

[tatus1969]

that is just a heating spiral, not an inductive hubhob.

[KL27x]

edit: deleted

(I just had to google "ceramic hob." I thought that was a different word for a halogen cooktop, which looks similar. When it's off, at least.)

[tatus1969]

edit: deleted

(I just had to google "ceramic hob." I thought that was a different word for a halogen cooktop, which looks similar. When it's off, at least.)

It's the second time this happened in this thread. As I am not native english, I may have chosen a misleading term. After some more googling, I think that this is the correct one: "ceramic glass halogen hob". It is basically a regular heating spiral covered in a thick layer of glass. They are very common in Germany.

Like this:

[SeanB]

Also called a glass top stove, very common as a built in item here as well. Benefits are easy to clean, and looks flatter than a regular stovetop with either heating plates or coils, but of course there are disadvantages in that it takes longer to heat up and it is a little less efficient power wise.

[Nusa]

https://www.merriam-webster.com/dictionary/hob

Definition of hob

    1    dialectal, England :  hobgoblin, elf

    2    :  mischief, trouble —used with play and raise always raising hob

Definition of hob

    1    :  a projection at the back or side of a fireplace on which something may be kept warm

    2    :  a cutting tool used for cutting the teeth of worm wheels or gears

    3    British :  cooktop

Definition of hob
hobbed; hobbing

    transitive verb

    1    :  to cut with a hob

    2    :  to furnish with hobnails

While dictionary correct, the cooker definition of "hob" seems to be specific to British English (maybe regional as well). In Americian English, most people would have no idea that a "hob" is a cooker. The word "cooker" is also uncommon, but it'll be understood since the word "cook" is in it. American terms are more likely to be stove, stovetop, range, cooktop or burners.

Iduction cooking is the exception to that rule. What little there is in US has been imported, and the importers call them "inductive hobs". Those of us who have heard of it at all, have probably heard of it in connection with induction. Hence the confusion.

In short, while your translation is correct, it isn't the best word choice for a global audience. There are a lot of regional/cultural language gotchas, and I'm sure you'll run into more of them. That's the difference between booklearning and actually talking to people.

[tatus1969]

That's the difference between booklearning and actually talking to people.

Not even booklearning, but hit-and-hope like googling random missing words To my apologize I can say that I went to the USA for four months during my study, and that was when I learned 80% of my English. Sold popcorn in Chicago in a movie theater that sadly does not exist anymore -> http://cinematreasures.org/theaters/409

[james_s]

In the US you'd almost always hear it called a "stove", occasionally "range". "Cooktop" is typically a separate unit used in conjunction with a wall oven.

I'd never heard the term "hob" until I started chatting with a guy from England.