The printed circuit boards of modern electronics can stand up to quite high temperatures. They have to, because they need to survive the heat of the reflow soldering oven. Well… technically they only need be designed to survive that heat two or three times for a few minutes each time. But still, usually they still are mostly functional even when the sensitive components are pushed past those manufacturer-specified limits.
So, you have a modern mobile electronic device that you want to repair with heat? Yes, remove all batteries, both the main power battery and the CMOS clock battery, if present. But what about the LCD screen? We’ve been told many times that when it comes to working with heat and LCD screens, you’ve got to be careful because too much heat can damage the LCD screen. So, how much is too much.
Never fear, I can consult the official manufacturer datasheet I found for one of the LCD screens I use, found from this previous blog article. Combined with other info I’ve found on the Internet, I have a verdict.
20201003/https://datasheet4u.com/datasheet-parts/LTN154X3-L06-datasheet.php?id=672537
20201003/DuckDuckGo lcd hot glue temperature range
20201003/https://www.ifixit.com/Answers/View/463364/What+is+the+suggested+temperature+of+a+heat+gun+to+remove+the+screen
20201003/https://www.ifixit.com/Answers/View/251709/Which+Temperature+on+LCD+Separators+is+free+of+risks
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60 degrees Celsius: Official manufacturer absolute maximum rating for long-term storage temperature, at maximum relative humidity of 27.7%.
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80 degrees Celsius: Hypothetical manufacturer accapted storage temperature provided that the relative humidity is extremely low. Low-range safe temperature for safely removing hot glue around a LCD assembly.
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100 degrees Celsius: Hypothetical manufacturer accapted storage temperature provided that the relative humidity is zero. Maximum temperature for safely removing hot glue around a LCD assembly.
The reason why the operating temperature is lower than the storage temperature is because the electronics themselves generate heat while in operation that needs to be dissipated, lest the temperature permanently damage the liquid crystal material in a cook-off. For the particular display I’ve referenced, the maximum operating temperature at the glass surface is specified at 50 degrees Celsius, 10 degrees lower than the maximum storage temperature. However, the heat dissipation of the display in operation is not specified.
So, now a point in hand. What is the reason why you are heating up an LCD? To remove water? Then you must be extra cautious and use lower temperatures, lestyou exceed the humidity-adjusted ratings. But, by contrast, if your LCD is dry to the regular air humidity levels, you can take up the higher temperatures, in this case exclusively for the purpose of softening hot glue.
So, coming back to the broader point. You want to bake off an electronic device whole to repair it? First important question: Does it have an embedded LCD screen? If so, your maximum temperature is severely limited to that one component. If you want to go higher, you must separate the LCD screen from the rest of the components. So, let’s build a temperature range chart for computer equipment.
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060 C: Maximum safe temperature for wet/humid liquid crystal displays
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080 C: Maximum safe temperature for dry liquid crystal displays
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100 C: Boiling water, maximum safe temperature for extremely dry, zero relative humidity liquid crystal displays
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140 C: Melting point of low-temperature hot glue., melting point of low-temperature heat seal connectors
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200 C: Baking with browning effects, spontaneous combustion of paper and wood, melting point and glass transition temperature of most plastics (LDPE, HDPE, PP, PMMA, PLA, ABS, PC), melting point of high temperature hot glue, melting point of leaded solder
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260 C: Lead-free reflow soldering oven, melting point of PS, PET, PVC plastic
That’s what it looks like! So, really a lot of the same chart details as my classic hot temperatures chart, but with a bit more detail on the low-end of the temperature range to indicate the temperature sensitivity of LCD displays. It makes sense that I have to use a separate chart for this listing because the lower temperatures in this scale don’t quite so much classify as “hot” temperatures.