Solder paste can be defined as a combining of metal solder particles with flux which is used during the assembly and manufacturing printed circuit boards. Solder Paste has a purpose, which is to create stable bonds between the PCB board’s plated connection pads and its electronic components added so as to form an effective electrical circuit. Flux density, composition, and size are all important factors playing significant roles in determining how a manufacturing process would be effective.
To understand how low temperature solder paste work, its applications, as well as other important solder paste features, continue reading our article.
How Low Temperature Solder Paste Works
In soldering, the solder paste formula of each manufacturer is different, their process of manufacturing is different as well, and their types would also have some important differences too
With respect to lead-free solder paste’s melting point, we can categorize it as low-temperature, middle temperature and high-temperature solder paste. From the name, low temperature solder paste is any solder paste having a low melting temperature.
The fact is Low-temperature solder pastes are extraordinary blends of sticky flux and small metal particles. They dissolve easily even at temperatures below 180 degrees Celsius. Normally the typical temperature for solder paste extends to about 259 degrees Celsius to 249 degrees Celsius, which usually becomes very destructive for delicate particles.
Furthermore, the exact reflow temperature of the solder paste is important to make sure that some components don’t surpass their highest temperature rating when assembly is ongoing. Also, low temperature solder pastes which melt at heat less than 180 degrees Celsius are utilized for these situations, as similar pasts usually reflow at a temperature of at least 259 degrees Celsius.
Pastes with low temperatures may also be utilized with those of higher temperature for applications needing two-stage assemblies. This means that some might need the attachment of components first, then other components included in the second step. Utilizing two reflow temperature pastes, the attached parts in the initial step with a high temperature paste may be unaffected by the application of the 2nd lower temperature.
Generally, solder melts between the range of 90 degrees Celsius and 459 degrees Celsius. Solder’s melting point can be engineered through the selection of solder blends as well as the device’s heat resistance power that is attached.
At What Temperatures will Solder Paste Melt?
Solders that contain different properties work with the exact melting firm whereby something hard becomes liquefied. Solders could melt from anywhere between 90 degrees Celsius and 450 degrees Celsius generally. This is why any solder’s melting point will change in line with your choice of solder amalgam, a device’s heat resistance power, etc.
You can divide solders into two main sections
- Non-eutectic solder and
- Eutectic solder
Non eutectic solder can’t melt at one temperature. There are non-eutectic alloys that have a range of melting between 2 degrees Celsius and 3 degrees Celsius. Also, some might have 75 degrees Celsius.
In addition, silver or hard soldering is seen whenever the melting of the solder paste passes the 450 degrees Celsius line and more.
What are the Applications of Low Temp Solder Paste
A good number of applications require low temperature solders which will reflow under 180°C. Also, optics assembly, LED attach, as well as the MEMS mounting of these need a low-temperature soldering. Over 100 metal alloys which melt below the conventional Sn/Pb alloy temperature are available.
The practical utilization of the low temp solder paste can be seen in our Electronics assembly industry in huge numbers. Now, let us consider when and how the low melt solder paste should be utilized.
Devices having Heat sensitive designs
There are devices which cannot just tolerate excessive heat and they are very fragile and delicate. Due to their heat sensitive nature, these devices easily get damaged when overheated. This is why the using a low temperature solder paste, your circuit board’s important components will be attached with temperatures falling within 180°C
Step Soldering
One important application of low temperature solder pastes can be seen in step Soldering. We can describe step Soldering as a regular soldering whereby circuit boards already have at least two permanent soldering thereby the PCB’s heat resistance power decreases. If you use higher temperatures rather than the low temperature solder paste, then the device’s portions will become affected and could be damaged beyond repair.
Other Low Solder Paste Temp Applications
- Low Temp Solder Paste is useful for removing the thinner flakes’ war page which could be caused due to higher heat reflow
- Prevents head-in-pillow and NOW failures
- Helps in low Tg flex circuitry for mobile phones, internet connections, cellular devices, etc.
- It fills in deformities present in the mating grounds as well as establishes a seal that is airtight.
- Useful in barometer, switches, systems for heat transfer, switches, as well as other forms of thermal designs
How to use the Low Temp Solder Paste?
In order to utilize low temp solder, there’s a need to have the right quantity of flux, appropriate temperature, and the skill and proficiency to attach specific work pieces.
Tin/indium, tin/bismuth, or silver/bismuth/tin are the most common selection due to their low rate of melting of 150 to 170 degrees Celsius. However you must be extremely careful during the blending of these components. You must also follow some important precautions. The SnBiAg alloy comes with a great melting point with a value of 138 degrees Celsius. This assures a huge heat reflow between 170 degrees Celsius and 180 degrees Celsius.
Though the combination of lead, bismuth, and tin have the lowest melting point value of 95 degrees Celsius, it can still lead to delinquency in joints because it can melt very easily in natural heat. Therefore there is a need to choose the components carefully, otherwise you’ll face serious damage or failure.
What are the Pros and Cons of Low Temperature Solder
Pros
- Lower costs of operation by reducing your need for more labor, energy, and materials
- Reduce any heat-related defect like voiding, head-in-pillow, and non-wet opens
- Gets rid of warpage for components that are thermally sensitive through the low reflow peak temperatures.
- Helps in improving the reliability of a product as well as first-pass yield on SMT lines.
- Alpha provides low-temperature preforms, cored wire, and solder pastes.
- Great wettability, full and even solder joints
- Has a melting point of 138 degrees Celsius
- Complies fully with the RoHS standards
- Great for fast printing and wide process
- No tin bridges and tin beads produced when reflow is ongoing
- The lifespan of the steel screen printing is long. Its pasting life is also long-term
- Eliminating omissions, great printability, agglomerations and depressions during the process of printing.
Cons
The major disadvantage of the low temperature solder paste is the composition’s bi element. Bi is a brittle component. This means that once soldering is completed, the firmness isn’t good.
The low temperature’s solder paste’s solderability isn’t as good as those of high temperature solder paste, then the solder joints gloss will be dark.
They have fragile solder joints, which aren’t suitable for products requiring strength, most especially for those products that need to be unplugged and plugged for the connecting sockets that can fall off easily.
Now how can we handle the disadvantages that come with low temperature solder pastes?
First, you cannot change the composition of low temperature solder paste and you cannot improve its firmness. This is why there is a need to retest the PCB board’s true temperature to be Blemto choose those that are available like the lower temperature solder paste and medium temperature solder paste. This firmness ought to be higher and you can select a high temperature solder paste that has a great welding effect and good firmness.
When these components can’t withstand the high temperature and can choose only the low temperature solder paste, then you need to use the other processes to help improve the firmness once the soldering has been completed.
What are the Differences Between Low Temperature Solder Paste and High Temperature Solder Paste?
Pure tin usually melts at 232 degrees Celsius, while pure lead melts at 327 degrees Celsius. This is why high temperature solder usually have lead most times.
For example, the pb88/Sn10/Ag2 alloy having 88% lead includes a melting point of 299 degrees Celsius. Components which would function in extremely hot environments like oil and gas well, automotive, and avionics, can enjoy the benefits of solders with higher temperatures.
Solders with low temperatures have different melting points that range from 47 degrees Celsius to 160 degrees Celsius. The solder alloys have Tin which is blended with different metals like Cadmium, Indium, Bismuth, etc.
Substrates or components such as flex circuits which are sensitive to heat are excellent candidates for the lower temp solders. Furthermore, step Soldering making use of low temp solder could be achieved without having to disturb the components that were previously soldered which were attached making use of the lead free standard alloys.
Conclusion
In summary, low temperature solder pastes are extraordinary blends of sticky flux and small metal particles. They dissolve easily even at temperatures below 180 degrees Celsius.
