Led coatings

[Prawn Connery]

Any proof that indeed Fluence and/or others use silicone conformal coatings ?
I had the impression that professionals opt always for the parylene conformal
coating (applied by chemical vapour deposition).

Furthermore ,in order for the silicone resin
to be an effective conformal coating ,
it has to form a film which is at least 40-50 times thicker than the effective
thickness of the acrylic conformal coating .As it becomes quite obvious ,
silicone conformal coatings absorb much more light from the source,thus
the output power losses are far larger than other coatings like acrylic or parylene.
That fact alone would rule out silicone as a conformal coating for
LED horticultural lighting ,where high efficiency is an attribute so much sought after in the art and trade ...

We've got one in the shop. Have you even seen a Fluence? Spiderfarmer also uses silicone. There are plenty of silicone conformal coatings designed specifically for LED applications and Cree, Samsung and others list them in their chemical compatibility charts.

Also, do you know much about parylene application? For example, do you know how large the average coating chamber is and do you understand this limitation in relation to mass production? Do you know how expensive it is and how much it would add to the cost of, say, a 4' strip (Fluence) or medium-sized LED board (Spiderfarmer)?

Finally, photon losses are a product of material density and transparency as well as thickness, so it is not just a matter of coating thickness.

It sounds to me like you've never actually done any conformal coating. But you do need to do a bit more reading

 

[Prawn Connery]

Everyone has the right to draw their own conclusions .
Maybe that Teknik gentleman discovered( and by now he is already aware of ) something that Cree,Bridgelux,Nichia,Citizen,Osram,
Samsung and others haven’t discovered yet and are completely unaware of ..

And what would that be?

 

[SDS_GR]

We've got one in the shop. Have you even seen a Fluence? Spiderfarmer also uses silicone. There are plenty of silicone conformal coatings designed specifically for LED applications and Cree, Samsung and others list them in their chemical compatibility charts.

Also, do you know much about parylene application? For example, do you know how large the average coating chamber is and do you understand this limitation in relation to mass production? Do you know how expensive it is and how much it would add to the cost of, say, a 4' strip (Fluence) or medium-sized LED board (Spiderfarmer)?

Finally, photon losses are a product of material density and transparency as well as thickness, so it is not just a matter of coating thickness.

It sounds to me like you've never actually done any conformal coating. But you do need to do a bit more reading

Well no,I’ve been always keen to DIY
and so never had the chance to see a light fixture from Fluence.
Still,personally I would not have chosen silicone as a material for the purpose. Acrylic is far superior material ,for the same price range .

I’m aware of the machinery needed for CVD coatings.Still all these companies -and they are more than a few-that apply Parylene coatings to LEDs ,
must have some customers ...
Otherwise the business would have been unsustainable.

I’ve applied more than a few times conformal coatings to various pcbs,but not on LEDs.
Yet,at least.

Thank you for your suggestion.
But I’m pretty much aware of the constant need for a bit more reading .
Nice to be reminded ,though ...

 

[Prawn Connery]

No worries. I'm glad we can keep it civil.

So, acrylic is in no way the superior LED conformal coating. It is less flexible and more susceptible to heat, so can crack under heating cycling. It can have pronounced colour shift and block useful (PAR) near-UV and UVA light. It has low chemical and moisture resistance – which are the reasons you would want to coat LEDs for horticulture. It does not adhere to surfaces as well as other coatings.

Two-part urethane is arguably a much better conformal coating for LEDs, as it can be applied thinly to retain light and is very strong and resistant. But it usually needs specialist application such as a selective coating machine.

Silicone is economical and provides excellent water and particle resistance. It is heat resistant and flexible. It has the ability to self-repair (close itself up) if it is cut. It can protect the LED a bit better from the odd soft knock as it absorbs impact and vibration. It is one of the best coatings for light transmission – why do you think almost all LEDS have silicone lenses?

Have a read below. Of course individual companies will argue that their choice of coating is best, so Electrolube might be a bit more biased towards acrylic and Chemtronics/Techspray more biased towards silicone.

Essential Guide to Conformal Coating

Conformal coating improves PCB reliability, providing increased dielectric resistance, operational integrity, and protection from corrosive atmospheres, humidity, heat, fungus, and airborne contamination such as dirt and dust. Conformal coating are a special polymeric film forming product that...

www.techspray.com

• Acrylic Resin (AR) – Acrylic conformal coating provides fair elasticity and general protection. Acrylic conformal coating is recognized for its high dielectric strength, and fair moisture and abrasion resistance. What generally distinguishes acrylic coating from other resins is ease of removal. Acrylic coatings are easily and quickly removed by a variety of solvents, often without the need of agitation. This makes rework and even field repair very practical and economical. On the other hand, acrylic coatings do not protect against solvents and solvent vapors, for example that might be typical for pumping equipment. Acrylic coatings can be considered basic entry-level protection, because they are economical and protect against a broad-level of contamination, but not best-in-class for any characteristic except possibly dielectric strength.
  
  
• Silicone Resin (SR) – Silicone conformal coating provides excellent protection in a very wide temperature range. SR provides good chemical resistance, moisture and salt spray resistance, and is very flexible. Silicone conformal coating isn’t abrasion resistant because of its rubbery nature, but that property does make it resilient against vibrational stresses. Silicone coatings are commonly used in high humidity environments, like outdoor signage. Special formulations are available that can coat LED lights without color shift or reduction of intensity. Removal can be challenging, requiring specialized solvents, long soak time, and agitation like from a brush or an ultrasonic bath.
  
  
• Urethane (Polyurethane) Resin (UR) – Urethane conformal coating is known for its excellent moisture and chemical resistance. They are also very abrasion resistant. Due to this and their solvent resistance, they are also very difficult to remove. Like silicone, full removal generally requires specialized solvents, long soak time, and agitation like from a brush or an ultrasonic bath. Urethane conformal coating is commonly specified for aerospace applications where exposure to fuel vapors is a common concern.

 

[SPLFreak808]

Wow shit got wild here, but some good info too..

I assumed that big brand LED chips would have chosen silicone due to its long term reliability when exposed to daily hot/cold/humid cycles, never used Si myself but I heard you can't just openly apply it in a random environment without a risk of trapping moisture.

 

[SDS_GR]

Nope I do not think that things got wild.This debate about which conformal coating is best for various LED applications goes on even between professionals.

Conformal Coating Recommendation

Conformal Coating Recommendation

www.circuitnet.com

How to choose conformal coatings that work over the long term

Global experts dealing in conformal coating solutions share insights on various considerations for purchasing conformal coatings for LED outdoor modules.

www.electronicsb2b.com

But we should indeed take a step back ,relax our minds and think clearly about what we are talking here...

Are we discussing which is the best option of various conformal coating chemistries applied by professionals with special equipment and procedures or are we discussing which option is readily available for the DIYer who wants to protect the possibly unprotected LED modules or COBs,with relative ease ,low risk and low cost?

 

[Prawn Connery]

Wow shit got wild here, but some good info too..

I assumed that big brand LED chips would have chosen silicone due to its long term reliability when exposed to daily hot/cold/humid cycles, never used Si myself but I heard you can't just openly apply it in a random environment without a risk of trapping moisture.

Silicone actually uses moisture to cure. That is why single part silicone cures faster in a high humidity environment, and why 95-100%RH at higher temperatures is generally specified for the accelerated curing process.

 

[Prawn Connery]

But we should indeed take a step back ,relax our minds and think clearly about what we are talking here...

Are we discussing which is the best option of various conformal coating chemistries applied by professionals with special equipment and procedures or are we discussing which option is readily available for the DIYer who wants to protect the possibly unprotected LED modules or COBs,with relative ease ,low risk and low cost?

Well I think for our industry we are generally talking about water-proofing PCB LED modules, such as strips, boards and stars etc. The main concerns, therefore, are water resistance, light transmission/colour shift and heat cycling. Economy and ease of application are also considerations, especially for DIYers. Even for mass producers this is a consideration, as parylene application needs specialist equipment and is quite expensive – even if it is arguably the best option.

For DIYers you are most likely to find an aerosol acrylic or silicone or even a urethane potting compound to do the job.

 

[SDS_GR]

But also silicone conformal coatings ,due to their thickness are more prone
to delaminate from thermal cycling .

( “ Think I saw an Irish youtube spiderfarmer SF1000 review where the coating was peeling back and appeared floppy. I made the assumption that it was silicone-based off that. “)

(...)
First, determine the expected operational temperature range for the circuit board – the highs and the lows. Should this be greater than 150-160°C, for example, it is almost certainly an application for a silicone, rather than an acrylic or polyurethane conformal coating. Also, consider the temperature excursions; if thermal shock or thermal cycling is not taken into consideration, it could lead to cracking, severely compromising a coating’s protective capabilities.

Second, what degree of chemical resistance is required? Acrylic materials, while easily removable when reworking, are generally highly susceptible to attack by solvents. Polyurethane materials, on the other hand, provide more chemical resistance but are generally not amenable to rework. Assess whether immersion or splash resistance is required and whether the coating may be exposed to heated solutions of potential contaminants, which will increase their ability to act as a solvent.

Third, consider what level of corrosion protection is required. Humidity generally only becomes problematic when condensation occurs, which would require close attention to the thickness and coverage of the coating. But do remember, while a thicker coating might provide superior protection in condensing environments or where salt-spray or corrosive gases are present, anything more than the 50 micron target thickness may be prone to cracking under conditions of thermal shock or thermal cycling.(...)

Why you should select the conformal coating for PCBs with care

The components used in printed circuit boards (PCBs) are sensitive to a host of environmental conditions that can have far-reaching consequences

www.electronicsb2b.com

EDIT:
I’ve not yet come across a specialised
LED silicone based CC in spray can
form ...
Any link(s) ?

I can relate with the “water proofing “ concept ,as those lights could be used in greenhouses or other facilities where water sprinklers are used for irrigation ,foliar feeding and spraying various phytochemicals.

Still these conditions are far different from the usual conditions inside the average
private grow tent or room .

Thus ,-regarding DIY designs -the sacrifice of total water proofing for gaining in other aspects like thin coating ,reworking and ease of application does not seem that important .

But yes ,
the acrylic CC does not fit
in applications with high temperatures involved.
But then,if such high temperatures are achieved ,that the acrylic CC will deteriorate by them -something is not right already .Efficient cooling of the LEDs will never allow an acrylic CC to deteriorate by high temperatures.

 

[Rocket Soul]

Wow shit got wild here, but some good info too..

I assumed that big brand LED chips would have chosen silicone due to its long term reliability when exposed to daily hot/cold/humid cycles, never used Si myself but I heard you can't just openly apply it in a random environment without a risk of trapping moisture.

This is what discourse used to look like here at riu when the Sanity Causus was more pronounced.

@SDS_GR you can find TEKNIK on ledgardener or the other place i showed you. He is a cool guy with a lot of experience and has a lot of experience sourcing leds thru china AND making sure they actually work at announced specs. He has 660s on par with cree xpgs now and several interesting products going up for sale soon.

He says the acrylics he tested had a hard time sticking to silicone based coverings and that most conformals base their ratings on white leds and for hortis (reds/uva)) the ratings are a bit useless. Hes still looking into what hed recommend cause he hasnt found something good, cheap and practical.

Edited

 

[SDS_GR]

Yes,acrylic will not adhere to silicone
LED LES or dome lens .And there is where the issues start to evolve .
Gets worse as the surface of the LES gets larger and as the acrylic coating gets thicker .

I really wonder what is this simple solution that Teknik has found ....

 

[Rocket Soul]

Yes,acrylic will not adhere to silicone
LED LES or dome lens .And there is where the issues start to evolve .
Gets worse as the surface of the LES gets larger and as the acrylic coating gets thicker .

I really wonder what is this simple solution that Teknik has found ....

Ooopsie that should read hasnt... sorry, i need to rretire my phone screen is f-ed

 

[Rocket Soul]

Can anyone say which type of coating would work best against vapours from burning sulfur against pm?

 

[Prawn Connery]

I know

But also silicone conformal coatings ,due to their thickness are more prone
to delaminate from thermal cycling .

( “ Think I saw an Irish youtube spiderfarmer SF1000 review where the coating was peeling back and appeared floppy. I made the assumption that it was silicone-based off that. “)

(...)
First, determine the expected operational temperature range for the circuit board – the highs and the lows. Should this be greater than 150-160°C, for example, it is almost certainly an application for a silicone, rather than an acrylic or polyurethane conformal coating. Also, consider the temperature excursions; if thermal shock or thermal cycling is not taken into consideration, it could lead to cracking, severely compromising a coating’s protective capabilities.

Second, what degree of chemical resistance is required? Acrylic materials, while easily removable when reworking, are generally highly susceptible to attack by solvents. Polyurethane materials, on the other hand, provide more chemical resistance but are generally not amenable to rework. Assess whether immersion or splash resistance is required and whether the coating may be exposed to heated solutions of potential contaminants, which will increase their ability to act as a solvent.

Third, consider what level of corrosion protection is required. Humidity generally only becomes problematic when condensation occurs, which would require close attention to the thickness and coverage of the coating. But do remember, while a thicker coating might provide superior protection in condensing environments or where salt-spray or corrosive gases are present, anything more than the 50 micron target thickness may be prone to cracking under conditions of thermal shock or thermal cycling.(...)

Why you should select the conformal coating for PCBs with care

The components used in printed circuit boards (PCBs) are sensitive to a host of environmental conditions that can have far-reaching consequences

www.electronicsb2b.com

EDIT:
I’ve not yet come across a specialised
LED silicone based CC in spray can
form ...
Any link(s) ?

I can relate with the “water proofing “ concept ,as those lights could be used in greenhouses or other facilities where water sprinklers are used for irrigation ,foliar feeding and spraying various phytochemicals.

Still these conditions are far different from the usual conditions inside the average
private grow tent or room .

Thus ,-regarding DIY designs -the sacrifice of total water proofing for gaining in other aspects like thin coating ,reworking and ease of application does not seem that important .

But yes ,
the acrylic CC does not fit
in applications with high temperatures involved.
But then,if such high temperatures are achieved ,that the acrylic CC will deteriorate by them -something is not right already .Efficient cooling of the LEDs will never allow an acrylic CC to deteriorate by high temperatures.

I saw that review. I think it was the overhang at the edge of the board that was peeling around the edges. It wasn't peeling off the board or LEDs.

There are some transparent silicone sprays out there that can be used for LEDs. Here is one and you can search for others: https://au.rs-online.com/web/p/conformal-coatings/0494714

I am not suggesting this is the best conformal coating for DIYers, merely providing a link.

 

[Prawn Connery]

Can anyone say which type of coating would work best against vapours from burning sulfur against pm?

For practical applications, look at urethane. But realistically, if you're going to use a sulfur burner for PM you could remove the light first, or just wipe it down after applying. Sulfur dioxide is probably not as big an issue as it has been made out to be. Plants do emit sulfur gasses but most horticulture operations have god ventilation.

 

[Rocket Soul]

For practical applications, look at urethane. But realistically, if you're going to use a sulfur burner for PM you could remove the light first, or just wipe it down after applying. Sulfur dioxide is probably not as big an issue as it has been made out to be. Plants do emit sulfur gasses but most horticulture operations have god ventilation.

Or perhaps covering the less in plastic while burning right?

 

[SDS_GR]

There are some transparent silicone sprays out there that can be used for LEDs. Here is one and you can search for others: https://au.rs-online.com/web/p/conformal-coatings/0494714

I am not suggesting this is the best conformal coating for DIYers, merely providing a link.

Thank you for the link.
It seems that most CC of any chemistry do have that nasty UV tracer
used for inspection .
Very difficult to find a CC without UV tracer.
That thing gets absorbed by the LES/lens of the LEDs and do cause a permanent CCT shift towards cooler temperatures.

 

[end_of_the_tunnel]

I'm wondering how safe these coatings are for the led packages. What about coeffients of expansion, as elements or parts of a package cycle through daily use. Could some coatings force things apart? Bit like rebar oxidising in concrete, or ice in brickwork. Are there unforseen consequences, that are at play and might be ignored whilst trying to gain market approval for some other percieved problem?

Its not like you are waterproofing more robust discrete components.

 

[SDS_GR]

Most of them are quite elastic and do follow the expansion-contraction rates of the components they are protecting.
Furthermore the coatings are so thin that most probably can’t exert forces that will displace soldered components .

 

[Prawn Connery]

There are silicone CCs out there without UV trace, however most conformal coatings appear to colour shift towards the blue spectrum, though it's not a huge issue if you are aware of it. You can compensate by using a bit more red in the spectrum.

Heat cycling was mentioned above in relation to expansion and contraction, but of more concern would be thermal management.