Silly question: Soldering temperatures?

[TriodeTiger]

I recall seeing some temperatures thrown out such as 250°C for 60/40 tin/lead solder, and higher temperatures good for lead free (SnAgCu), however upon looking at what exactly to set my Hakko to, to compare joints at different temperatures, I find that the Hakko disagrees.

For example, this old albeit well written guide: http://www.elexp.com/t_solder.htm
The chart states: 60/40 - 374 degrees F (190 degrees C)

And some Freescale document, which was the second thing I found: http://www.freescale.com/files/microcontrollers/doc/app_note/AN3300.pdf

SnAgCu has a melting temperature of 222°C, compared
to the regular SnPb sphere of 183°C. T

Why do I ask? The Hakko FX-888 has its minimum temperature at 200°C.

Does flux not care as much with temperatures in the 200-250 range, as long as I am careful with my soldering and give it a chance to do what it needs to? Are irons now made more towards lead free solder? I can't imagine what on earth I would heat it up to 480°C for, unless it's some work on a crazy thick lead-free blob holding down a TO-220's tab or something (reminds me of Dave's example in his soldering tutorials), however a larger tip is probably better than half a thousand degrees.

Tempted to buy lead-free if it will just work more appropriately with the iron, will keep my mind at ease from lead blobs and dust finding their way on to my desk which I use for other work often.

[IanB]

A good temperature setting for tin/lead solder is 350°C. You want to set the temperature high enough that the solder flows and wets the surfaces well and so that the flux is fully activated.

[T4P]

Lead "dust" Buddy, how does lead grind itself at 300C ? They can't . They just can't . Unless it's lead free where it's so easy to reform after melting therefore making those annoying "dust"

But best is 350C nothing more then that for leaded solder,

[Mint.]

I use about 350°C for my 60/40

[EEVblog]

325-350C seems to be the most widely used for 60/40 solder.
Yes, solder melts at a lot lower, but the thermal coupling between your tip and the component and the pad and solder is very far from perfect. So you need a higher temp to compensate.
Reflow soldering gets away with lower temps because it's all ramped up and "pre-heated" first.
Hand soldering is different, you need to go from cold to soldering temp in a second or two.

Dave.

[TriodeTiger]

Righty. I will test different temperatures on clean/oxidised surfaces and remember the results. Even with the internal flux if they differ in quality I'll at least know if temperature/oxidation is a factor.

Lead "dust" Buddy, how does lead grind itself at 300C ? They can't . They just can't . Unless it's lead free where it's so easy to reform after melting therefore making those annoying "dust"

I can dent leaded solder with my fingernail and light pressure, so it is conceivable I can scrape it off and get it under my fingernails/on desk. While tinning my cheap firestarter iron it globbed in to small beads when it could not adhere and go down on to my desk, thought I'd prefer it being lead-free, however those two scenarios are less relevant unless I am doing something crazy

Will buy lead-free compatible tip (if it needs one) and at least get experienced with it for now, probably won't move to it unless I concern with others' safety rather than my own.

[T4P]

Righty. I will test different temperatures on clean/oxidised surfaces and remember the results. Even with the internal flux if they differ in quality I'll at least know if temperature/oxidation is a factor.

Lead "dust" Buddy, how does lead grind itself at 300C ? They can't . They just can't . Unless it's lead free where it's so easy to reform after melting therefore making those annoying "dust"

I can dent leaded solder with my fingernail and light pressure, so it is conceivable I can scrape it off and get it under my fingernails/on desk. While tinning my cheap firestarter iron it globbed in to small beads when it could not adhere and go down on to my desk, thought I'd prefer it being lead-free, however those two scenarios are less relevant unless I am doing something crazy

Will buy lead-free compatible tip (if it needs one) and at least get experienced with it for now, probably won't move to it unless I concern with others' safety rather than my own.

You must think about the temperature ramp of your station because the normal 936 meets the spec just nice but the more powerful ones like the 951 are easier for lead free because their ramp up is near instant

[free_electron]

No, this is not a silly question. Many people have problems with this because they do not understand what is going on.

The problem is more complex...
If your soldering iron was perfect in terms of giving off its heat you could perfectly solder regular snpb 63/37 at 184 degrees c ( 63/37 is the eutiectic alloy, meaning it melts exactly at a given temperature, in this case 183. 60/40 is a cheaper non eutectic alloy that is 'syrup' in a narrow band. 185 to 190 degrees. Eutectic materials transition from solid to liquid at 1 point, non eutectic allows transition slower , which can lead to brittle solder joints... )

Now, in real life you have to deal with a number of factors:

The thermal resistance between the tip and the , to be soldered elements.
The thermal inductance. It takes a while to get the heat in....
The thermal capacitance of your iron. If you start pulling heat out of the tip it takes a while to replenish that.

The thermal capacitance is determined by two things : thermal mass and electrical power.
If your soldering iron has a lot of metal and a big fat tip it has a big 'buffer'. If the iron itself has a lot of electrical power it can replenish the missing heat very quickly. A good soldering iron for electronics should have 80 to 100 watts.

The thermal inductance you have no real control over. It is mainly determined by the parts that need soldering. If you have to solder a small sot23 there is virtually none... If you need to solder the pins of a through hole heatsink ... Yeah there's plenty there...

The thermal resistance is a matter of correct soldering technique. Never,ever solder 'dry'.
The correct method is to apply a bit of solder to the tip first , put the little blob of tin in contact with the pin and pad to be soldered , wait until it flows and then add a bit more solder if needed.
This lottle blob of pre-melted tin on the tip ensures good thermal transfer. If you tip is 'dry' there is very little contact surface. That little blob of tin mitigates this.

So , how Do we traditionally compensate for the shortcomings of our soldering station? By jacking up the temperature ... Which is totally WRONG !

You need to use an appropriately sized tip for what you do and you need an iron with enough thermal mass. That is why , on a real assembly floor, the technicians have 2 ,3 or more different irons with different tips and they cycle according to what they are soldering.

On the subject of flux.
Flux activates at a very low temperature. Most fluxes kick in at about 90 to 120 degrees c.
Flux is an element that improves the wettability of the , to be soldered, elements. Wettability is a measure for how good solder flows. For example : sprinkle some water on a glass plate and it will form beads. This is poor wettability. Add some soap and it flows nicely.
Flux is just that : it is 'soap' for solder.
Flux does two things: it lowers the surface tension of the solder which allows solder to flow better, instead of forming beads. But it is also ahighly reactive compound. Flux has the capability of ripping oxygen atoms out of binding with other elements. If your copper pad has a thin film of copper oxide on it the flux will rip the oxygen out of binding with the copper and transform copperoxide back into copper. At the same time the flux covers the now clean copper , preventing re-oxidation.
Flux needs some time to react... The fluxes in solder wire are much more reactive than fluxes in solder paste. Paste is intended for slow heating .. Over a time of minutes. Where as solderwire has to melt in seconds. So the flux needs to be more agressive. It has a shorter time to work.

Here is a problem though : flux evaporates when heated. The mass of the solder is large enough to push it out of the way, but, if the temperature is too high , the flux evaporates too fast and it will 'spatter' you will get little beads of flux all over the place. Its like a mini eruption... Worst case this mini eruption flings pieces of liquid solder around as well...
If you run it so hot the flux also falls chemically apart and can no longer do its work.

So, what is the correct answer for the question: what is the correct temperature for the soldering iron?
The answer is: the lowest common denominator of all these factors.... In this case .... The flux !
Followed by what alloy of solder you are using.

You go look up the datasheet of the solder you buy, and you really need to go to the specific manufacturer and model , because every manufacturer has different fluxes !
In that datasheet they will give you the 'working band' and optimum temperature.
And that's it. Those numbers are tuned for that particular solder. Now, in practice they will be pretty close between manufacturers, although there can be some differences. Few tens of degrees c.

If you solder joints are still no good : you need more thermal mass and power , or your soldering technique is simply no good.

[Bored@Work]

You need to use an appropriately sized tip for what you do and you need an iron with enough thermal mass. That is why , on a real assembly floor, the technicians have 2 ,3 or more different irons with different tips and they cycle according to what they are soldering.

A common beginner's mistake is to use a too small tip. For example an ultra fine needle tip. As a rule of thumb, use the largest tip you can get away with. Large, but not so large you damage nearby components, solder joints or the PCB material. Chisel size.

[IanB]

The thermal resistance between the tip and the , to be soldered elements.
The thermal inductance. It takes a while to get the heat in....
The thermal capacitance of your iron. If you start pulling heat out of the tip it takes a while to replenish that.

The thermal inductance you have no real control over. It is mainly determined by the parts that need soldering. If you have to solder a small sot23 there is virtually none... If you need to solder the pins of a through hole heatsink ... Yeah there's plenty there...

One small quibble here. There is not actually a thermal inductance property in the thermal/electrical analogy. Only thermal resistance and thermal capacitance properties exist. Given a suitable driving force heat flow commences immediately with no time delay associated.

All time varying effects come from thermal capacitance alone (or from external inputs).

[kaptain_zero]

Why do I ask? The Hakko FX-888 has its minimum temperature at 200°C.

Don't get too hung up on the temperature scale on your FX-888. It's more of a guideline than actual temperatures. I checked my old 936 and my new 888 with a Hakko tip thermometer and the FX-888 out of the box was off by 50 degrees compared to the 936. I adjusted the 888 to track the same as the old 936 so that no matter which iron I'm using, I know from past experience where to turn the knob for a particular tip. As I had already gotten used to setting the knob on the 936 to given temp for each tip I use, there seemed to be no point in adjusting the 936 to read correctly, as it would just throw my memory off.

Regards

Christian

[T4P]

Why do I ask? The Hakko FX-888 has its minimum temperature at 200°C.

Don't get too hung up on the temperature scale on your FX-888. It's more of a guideline than actual temperatures. I checked my old 936 and my new 888 with a Hakko tip thermometer and the FX-888 out of the box was off by 50 degrees compared to the 936. I adjusted the 888 to track the same as the old 936 so that no matter which iron I'm using, I know from past experience where to turn the knob for a particular tip. As I had already gotten used to setting the knob on the 936 to given temp for each tip I use, there seemed to be no point in adjusting the 936 to read correctly, as it would just throw my memory off.

Regards

Christian

Yeah ... just before switching off the triac it goes off by 12C even after cal. well i cal'd it with my meter so no complaints

[TriodeTiger]

No, this is not a silly question. Many people have problems with this because they do not understand what is going on.

The problem is more complex [...]

This is thoroughly helpful to me, my mind often finds information hard to interpret and that worked very well. I'd love to look to see if the solder I have has a datasheet, and view the datasheets of all types of solders I will be working with in the near future to get an idea of how they differ from just "60/40". It would be neat to compare different brands and alloys and see how I can exploit them for better work.

Don't get too hung up on the temperature scale on your FX-888. It's more of a guideline than actual temperatures.

Thankfully I have an IR thermometer with a ceiling at 230°C. If I set my FX-888 to 200°C I can try to find if there is any offset, at least at that range. Hopefully I can get accurate enough readings on something metal, I am sure not much IR going to reflect anywhere anyway. Reading windows and free space seems accurate enough with it.

A common beginner's mistake is to use a too small tip.

My conical firestick could not even heat up solder wick, I was glad the Hakko came with a reasonable sized chisel-like tip. I plan to purchase a few on eBay as needed being so available and cheap (even if they are lesser quality, I can buy many)

[kaptain_zero]

Thankfully I have an IR thermometer with a ceiling at 230°C. If I set my FX-888 to 200°C I can try to find if there is any offset, at least at that range. Hopefully I can get accurate enough readings on something metal, I am sure not much IR going to reflect anywhere anyway. Reading windows and free space seems accurate enough with it.

You can use 63/37 solder to discover if your lowest setting is above or below it's melting point, as it's melting point is exact. It would be more accurate than an IR thermometer.

To quote from wikipedia:
 
 The 63/37 is a eutectic alloy, which:

• has the lowest melting point (183 °C or 361.4 °F) of all the tin/lead alloys; and
• the melting point is truly a point — not a range.

Now, as for soldering iron temps, here are some reasons why it's not that important to know the exact temperature and what one should base ones settings on and how that differs from when digital readout, calibration and process control are required.

Repair techs and hobbyists, typically work with all sorts of components of various sizes and age, some perhaps recycled from other projects. The boards we use may be new, old or home made and have varying degrees of oxidization. Components used in a typical project we might work on can vary greatly in size etc. All these things make it difficult to set an exact temperature on your iron, sometimes you need a little more, sometimes a little less. The main things we look for are sufficient heat to make the soldering quick, and minimizing excess heat as that simply oxidizes the solder/tip faster than necessary. So we shoot for keeping it hot enough for the job at hand and attempt to avoid having it too hot as it just makes tip cleaning required more frequently and wears out the tip faster. If one runs into a problem, turning up the heat might help out... If fighting with the tip to keep it clean, one probably has the heat up too high.

In a production setting, things are quite different. All components are virgin/new and completely clean. When production hand soldering, careful control of the temperature becomes possible as components etc. are grouped for installation in such a way that the required tip temperature remains constant. Solder and fluxes are carefully selected, tip temp is set to the minimum temp required for reliable joints and to minimize the chance of heat damage while prolonging tip life. In other words, not your typical rough and tumble hobbyist situation. 

I would not worry about checking the temps on your iron. Just turn it up gradually until is seems to work well. Once you've used it for a while, you'll find the knob will settle in at some number that you remember... and eventually, you'll just look at a joint you need to solder and instinctively know when you need to turn the heat up or down.

Regards

Christian

[free_electron]

The boards we use may be new, old or home made and have varying degrees of oxidization.

thats why you want to make sure of two things :
1) Give the flux time to do its work ! That means the CORRECT setting so you don't evaporate it or carbonize it too quickly.much too hot and you end up with black sticky goop that actually prohibits good flowing. Too hot and it spatters allover the place.
2) use the correct type of flux. If you are soldering older parts with oxidation go for an RMA style or even an RA flux. Rma = rosin, mildly activated. Ra = rosin activated. That is really agressive flux.

It is important to clean up rma and ra type fluxes as they can be conductive in the 100 kilohm range, especially if you have been cooking them for long and they turned black. Iospropyl alcohol or real fluxoff ( chemtronics is the absolute king here, both for fluxoff and solderwick) works best.

Components used in a typical project we might work on can vary greatly in size etc. All these things make it difficult to set an exact temperature on your iron,

this is totally false !

The size of an object has NOTHING to to with temperature ! It is all about thermal mass. You can fry a mosquito with a match just as you can fry an elephant with a match, it will just take longer... Because your match has too little thermal capacity.

Use the correct tip (not a skinny point, those are for tqfp pins ) preferrably a short chisel or 'screwdriver tip' and have an iron with some 'kick' minimum 80 watst with a heavy supply and fast reacting control loop.

Chisel tips have the advantage that you can use them broadside or thickness wise.... Use the wide side for big objects , rotate 90 degrees for skinny stuff.


 

wears out the tip faster.

temperature does not wear out the tip faster. ( unless the plating peels off but then the tip was crap to begin with )

The tip wears out because part of the iron dissolves in the solder ( it must ! Otherwise the solder joint does not work ! ) the higher the tin concentration the more iron dissolves. That is why we have so called ' lead free compatible' tips. The difference sits in the thickness of the iron plating. A solder tip is a solid copper slug ( for good heat transfer ) plated in iron ( for solderability ) and coated with chrome where no solder is allowed to go. Once the iron gone the tip is shot...

The proper way to treat the tip is to:
- clean it off on a damp spunge ( not soaking wet ! Otherwise you have thermal shock ) swiftly to remove as much excess tin as possible and put the iron its holder. The fewer tin the less plating will dissolve ( it's a self terminating process )
- when taking up the iron , add some fresh solder , wipe off , add some more fresh solder and use this last blob to male the joint. Never ever solder 'dry'. ( i explained that before )
- do not use any abrasive stuff like knives , files or whatever in an attempt to clean the tip.
Even though those copper curls work well , they are not so good for the tip and should be used sparingly. Best is the tip cleaning pellets sold by kester , multicore , weller and others. This holds an agressive flux and a hard solder alloy. It cleans the tip thoroughly, poke the tip in the tablet and spin it around a couple of times, wipe off to remove agressive flux , apply fresh solder, wipe off again and put iron in holder.

 

If one runs into a problem, turning up the heat might help out...

 cranking up the heat is NOT the correct solution. Check if you are using the right flux and a correctly sized tip.
There is a reason that there are tens of fluxes out there. Learn what should be used when and simply keep a few rolls of solder at hand. I got 4 or 5 rolls of solder. One medium thickness RA style flux 63/37, 3 thickness water soluble 63/37 and one fine rma.

In other words, not your typical rough and tumble hobbyist situation. 

just because we are hobbyists is NOT an excuse to abandon strife for perfection. Just do it right.
It doesn't cost any extra money. A roll of solder cost you 15$ and lasts a long time. A good quality tip costs 5$ and , if properly treated, will last  5 or more years in hobby setting. So you actually save money in the long run.
 I have several tips that are 7 or more years and they are powered up at least 8 hours a week.

[TriodeTiger]

I've just used it for the first time - touching up a poorly before done LCD display header. It cleans nicely with the springy metal fluxy stuff, silicone wiper and sponge and I am happy with that. Solder wick that is >0.5cm in width is on my list

Also created the "perfect joint" twice - if it so exists.

One concern, best a picture show it:


At very end is uneven tinning, will work on that, however almost exactly 1.2cm from the tip is a *perfect* circle where burnt flux remains going back a few mm as seen. I've tried cleaning it briefly, however cleaning and solder work only easily on the tip.

I assume it would be all right as-is, seeing how it had created a border for itself. Does only keeping the tip past that point clean matter? Should I try to heat the iron up and clean it off the best I can? Is the coating not at that point?

Edit: If I hadn't used a cardboard surface, I probably wouldn't have spotted sparkle-sized skin-sticking pieces of SnPb, makes me want to try Pb-free more.

[T4P]

There's a massive list of no-no's to lead free but i will spare you that 

[kaptain_zero]

At very end is uneven tinning, will work on that, however almost exactly 1.2cm from the tip is a *perfect* circle where burnt flux remains going back a few mm as seen. I've tried cleaning it briefly, however cleaning and solder work only easily on the tip.

I assume it would be all right as-is, seeing how it had created a border for itself. Does only keeping the tip past that point clean matter?

This is perfectly normal. That is the border between the iron coated tip and the chrome plating where solder will not stick and that protects the core from oxidation. Don't worry about that ring, just keep plenty of solder on your tip when not in use, clean just before using and then reload with more clean solder before placing back in the stand. Don't let your iron sit hot if it's not going to be used for longer period of time. Don't get too carried away with cleaning your tip, cleaning can wear the coating on the tip.  Whenever I use solderwick, I find that the tip can get dry so I take a little extra time to get the very tip re-wetted with solder... It may be related to the brand of solderwick that I use.....

Regards

Christian

[StubbornGreek]

This is a very good thread (filled with great info). The one thing I would like to interject is that once you've gotten used to your soldering iron and have been using it for a while (you tend to set the same temp over and over - it becomes habit once you're comfortable) to once in a while check the heating element inside your equipment. These wear down (albeit after good amount of time) and need to be replaced from time to time. The degradation is gradual so if you use your iron often, you'll mentally compensate (by leaving your iron on the work longer) for the diminished heat - not good as you can damage components with prolonged exposure to high heat.

Also, a good start for any beginner would be the Pace videos on youtube, excellent stuff.

[free_electron]

@stubborngreek : good luck checking your heating element ... they are potted in a ceramic compound so there is no way getting to them apart from sawing the thing open and destroying it.

and fiddling wit the temperature setting is not necessary. use the correct one. There is a reason the really high-end soldering stations like metcal and weller actually do not have a temperature adjust. in metcal the tip temperature is defined by the tip . no changing it. and the high end wellers have an operator lockout mode. the station is set up for the solder used and then 'frozen'. no changing it by the operator. There is simply no need for it. if you need to mess with the temperature constantly your soldering technique is wrong !

[M. András]

my wrmp pencil has the rt3 tip which is small 0.4x1.3mm chisel tip, it makes nice joints pretty fast less then a sec around 300-350degree celsius  and almost instantly regains its temperature, i didnt try wider wicks then 2.2mm but with a little solder on the tip it makes wonders. ohh and its only a 40 watts tip i use a stannol krystall 505 solder it makes nice amount of fumes but its wont change at diff temps. i could make nice joints with an old 220volts 60 watt soldering iron with a huge 4mm tip, but with this i can make wonders

[kaptain_zero]

and fiddling wit the temperature setting is not necessary. use the correct one.

How does one *find* the correct temperature with the OP's soldering station *without* fiddling with the adjustment knob?

There is a reason the really high-end soldering stations like metcal and weller actually do not have a temperature adjust. in metcal the tip temperature is defined by the tip .

I see that Metcal offers different series of tips with differing temperatures, handy to have if you cannot adjust the tip temperature yourself. Hopefully, each tip cartridge is engineered to have the same final tip temperature, no matter the thermal mass size of the tip. The Hakko units have different size and shaped tips which do not heat to the same temperature with the same heat setting. Better or worse? No, just a different way of accomplishing the same goal.

and the high end wellers have an operator lockout mode. the station is set up for the solder used and then 'frozen'. no changing it by the operator.

The Hakko's have lockout available as well. No need to lock it out if the job changes constantly and the operator knows what they are doing. In manufacturing, you're often dealing with issues of lesser skilled labourers who might be tempted to crank up the temperature to boost their piecework rate despite the drop in quality, to make more money. 

There is simply no need for it. if you need to mess with the temperature constantly your soldering technique is wrong !

To this we agree, there is no need to constantly fiddle with the settings, just sneak up on it until you find the right setting and leave it there until circumstances change. Example:  When I have to swap out my 0.8mm or 1.2mm chisel tip for a 4mm chisel tip, because I'm soldering heavy duty connectors onto a coax braid, or using 8 gauge wire with their required heavy connectors, you can bet your bottom dollar that I'll need to crank the heat up vs soldering  tiny surface mount components with my smaller tips. Metcal does that by engineering each $25+ tip cartridge... my Hakko with it's lower cost replaceable tips on the same heating element does not adjust that for me... that's why I get a knob to twiddle on my Hakko.

Regards

Christian

[free_electron]

How does one *find* the correct temperature with the OP's soldering station *without* fiddling with the adjustment knob?

You take the datasheet of the solder you have on hand and look it up ! anything else is just wrong.

I see that Metcal offers different series of tips with differing temperatures, handy to have if you cannot adjust the tip temperature yourself. Hopefully, each tip cartridge is engineered to have the same final tip temperature, no matter the thermal mass size of the tip.

Thermal mass is only important to compensate for the size of the object to be soldered. the temperature remains the same. The solder always melts at the same temperature ( for the specific alloy you have at hand ), irrespective of how large a surface you need to heat.

The Hakko units have different size and shaped tips which do not heat to the same temperature with the same heat setting.

I'm going to be very harsh here , if this is indeed the case : hakko -> garbage can.  If the size of the tip changes the temperature then the control loop is garbage ! A proper soldering iron has a heating element and a sensor and employs a closed loop regulation system. Some soldering irons can measure the temperature by measuring the resistance change of the heating element. But the principle is still a closed loop regulation.

If the tip temperature changes with mass then they are simply using an open-loop  pwm regulator and that is not correct !

When I have to swap out my 0.8mm or 1.2mm chisel tip for a 4mm chisel tip, because I'm soldering heavy duty connectors onto a coax braid, or using 8 gauge wire with their required heavy connectors, you can bet your bottom dollar that I'll need to crank the heat up vs soldering  tiny surface mount components with my smaller tips.

Again : this does not make sense ! The melting point of your solder has not changed .... so why do you need to change the temperature setting ?
If you need to heat a larger surface use a larger tip or a tip with more mass and have a station with 'breathing room' meaning i beefy power supply that can crank power in the tip to raise it to the correct temperature in a shorter time. power is not the same as temperature. Power defines how fast you can reach a given temperature.

[StubbornGreek]

@stubborngreek : good luck checking your heating element ... they are potted in a ceramic compound so there is no way getting to them apart from sawing the thing open and destroying it.

and fiddling wit the temperature setting is not necessary. use the correct one. There is a reason the really high-end soldering stations like metcal and weller actually do not have a temperature adjust. in metcal the tip temperature is defined by the tip . no changing it. and the high end wellers have an operator lockout mode. the station is set up for the solder used and then 'frozen'. no changing it by the operator. There is simply no need for it. if you need to mess with the temperature constantly your soldering technique is wrong !

I'm confused. Here is a shot of what I'm referring to:

Soldering Iron with Heating element installed:



Replacement Element:



Another Element for Hot-Air Tool:



I've done the same to a weller in the past. Miscommunication?

EDIT: Oh, I re-read my post, I could have mentioned that you'll need a thermocouple to check your current gear. Is that where I misrepresented myself?

[free_electron]

Here is a shot of what I'm referring to:

Well exactly. That is the ceramic compound. You cannot open that. besides why would you want to inspect that ? What do you think you will be able to see ? it either works or it doesn't. If it doesn't -> garbage can.
There is no 'inspection' that can be done. Apart from maybe cracks in the ceramic element. The soldering irons that i use  (WSP80 and MT1500) you cannot even remove the cermic part it is cast in the steel sleeve.