Discussion on temperature adhesives

Starting from the contact adhesive, it is often heard from customers on the adhesive temperature requirements, the common glue used in electronic assembly package because often require too reflow or wave soldering, naturally temperature resistance of the adhesive request. Also receiving a lot of adhesive reliability testing, they also often have a thermal shock or high temperature and humidity requirements, here temperature is also set forth requirements. On adhesive temperature resistance from us to explore the following aspects.

About temperature resistance or high temperature capability, we first need to define the time and temperature of the cycle issues.
1) The first refers to the ability to instant adhesive temperatures (a few seconds to a few minutes, the cumulative number of times a certain limit).
2) The second cumulative means of adhesive can withstand a temperature (cyclic or acyclic work, every few minutes to several hours or even longer, in principle, limited cumulative number)
3) The third is the ability of the adhesive to work continuously at a certain temperature

The above three cases on the actual we can further understand the difference:
1) In the first case, for example, a conventional SMT red plastic inside the wave soldering temperature resistance to belong to this category, certain products or sealed plastic COB bonding SMT process and then went through a few seconds of wave ( about 250 degrees) or minutes of reflow (about 150 degrees). There is required to pass the test after this temperature adhesives basic performance and functionality remain unchanged. Generally adhesive glass transition temperature Tg point higher after curing, which aspects of performance will be better. Of course, the thermal expansion coefficient, modulus and the like also have a greater impact;
2) The second case in the adhesive reliability testing often encountered, such as high and low temperature test, a common dual 85 tests, and some are from room temperature to about 150 degrees tens or even hundreds of thousands of cycles, each cycle a few minutes to several hours, but also from below zero to 100 degrees. Of course, there is the test of overall performance adhesives, not just the temperature resistance;
3) The third refers to the continuous operating temperature of the adhesive, this is the most demanding temperature requirements. Generally common organic polyurethane or epoxy adhesive, whether or silicone and so on are actually more difficult at temperatures exceeding 500 degrees continuous work. PI have seen some kind of organic adhesives can continue to work in 300-degree temperature, but it is actually curing at 250 or higher. Some inorganic adhesive in the case of 1000 degrees or more can work, for example in the aerospace and other fields. In fact, a little sense of inorganic adhesive similar electronic slurry temperature sintering paste, and eventually almost all inorganic volatile, while the crystalline structure formed by a combination of a connection or gluing.

He recently studied a high-temperature glue can be used for the speaker 360, the data show can continue to operate at high temperatures 312 degrees (in fact, should belong to the second case, no speaker will be open all year long, huh, huh). It found that such glue actually has a lot of solvent inside was completely cured estimate the remaining cured even less than 50% by mass. I looked at the product MSDS data belonging nitrile phenolic adhesive, and methyl ethyl ketone solvent to do. Incidentally, in which the epoxy adhesive formulations by adding phenolic resin and some of the filler can improve the product temperature resistance. Commonly known as Bakelite Bakelite, due to its insulation and heat resistance can be used in many electrical and electronic products.

Further adhesive temperature resistance and curing conditions often have a great relationship, generally require room temperature curing adhesive resistant to high temperatures actually have some difficulty. Similar to the aforementioned high-PI-resistant glue curing temperature requirements are relatively high. Also in some cases be segmented sub-zone temperature curing can enhance a sense of adhesives or reliability.

These are the author's own experiences and views of some messy.

"For high temperature adhesive definition, classification and evaluation of domestic and international standards have not yet unified. In general, high temperature should be in accordance with the specific temperature, time and media designed to maintain the required bonding strength or have a certain strength retention That rate is to evaluate temperature adhesives in addition to meet the requirements of a certain temperature, but also must meet the following overall performance: good thermal physics and thermal and chemical properties; good workability; at higher temperatures and the use of work Under the conditions, there is a high adhesive strength and good mechanical properties and within a specified period of time to maintain this performance. "

"High temperature glue
I. Where the following conditions are generally considered to be regarded as high temperature adhesives.
(1) Long-term use (cumulative 1 ~ 5a) at 121 ~ 175 ℃ or at 204 ~ 232 ℃ cumulative use 20000 ~ 40000h.
(2) Under the cumulative use of 260 ~ 371 ℃ 200 ~ 1000h.
(3) the cumulative use at 371 ~ 427 ℃ 24 ~ 200h.
(4) 2 ~ 10min at 538 ~ 816 ℃.
(5) 1250 degrees below the gum
(6) 1750 degrees below the gum
Second, the common high-temperature glue:
High-temperature plastic by nature can be divided into organic and inorganic high-temperature hot glue glue two categories.
1, common organic high-temperature plastic:
Common high-temperature plastic Temperature range generally at 400 ℃ for it, which mainly include silicone rubber, phenolic resin, urea-formaldehyde resin, temperature epoxy adhesive, polyimide plastic. Such adhesive may have a soft elastic, or toughness, or hard rigid. Such gum can generally be added to a functional filler, given its insulation, thermal, magnetic, fire retardant and other functions.
2, inorganic high-temperature plastic:
Inorganic refractory glue temperature can reach 1800 ℃, can be a long time in the fire, broke the world high temperature adhesive temperature only technical problems in 1300 ℃ below, ××× refractory inorganic binder is a Species use of inorganic nano-materials made by the condensation reaction of refractory inorganic nanocomposite binder composition ratio and filter by process parameters to obtain the binder is a neutral PH value of suspension dispersant system, not only bond strong and non-corrosive metal substrate, and can maintain good adhesion properties and corrosion resistance at high temperatures and then, long service life. Direct bonding ××× refractory inorganic binder easy to use, can be used for high-temperature materials, paint directly on the substrate surface temperature spraying 400-1000 ℃ in evaporation of water at the same time, the paint will adhere to the substrate surface instantly high temperature protective coating has a uniform, dense, good thermal shock resistance, protective effect is significant.
Sealing high-temperature plastic profile:

Currently sealed type high-temperature plastic single-component silicone rubber-based, general temperature below 260 ℃, few manufacturers models can do 310 ℃, two-component silicone gel is reported to have done 400 ℃ of.

Adhesive filled with high-temperature plastic profile:

Currently below 250 ℃ modified in various high-temperature epoxy adhesive mainly, 250 ~ 400 ℃ silicone-based resin adhesive, should be used and generally over 400 ℃ inorganic adhesive.

Inorganic high-temperature plastic brittle, high peel strength is generally low shear strength. Generally used for bonding or fixing bricks, asbestos, ceramic, or between these materials and steel. "