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Basics of the SMT Reflow Soldering Temperature Plate

Dec 31, 2018 8:00:00 PM

Reflow soldering is the most common method used by SMT to bond electronic components to printed circuit boards. Reflow soldering refers to the use of solder paste (a mixture of solder and flux) to connect one or more electronic components to a contact plate and then melt the solder by controlled heating to achieve permanent bonding.

In a previous article, we mentioned the SMT reflow soldering temperature curve and its four parts. This article presents more information about the plate used to do the heating. 

 

liam-briese-1120916-unsplash-689634-edited-784290-edited

 

 

Thermocouple wire model plates listed in the table below.  The first column is the insulation type, including TT, KK, TG, and GG. ANSI color type KK is the most common type.

 Thermocouple wire thermocouple wire models

 

 

Temperature point selection

To measure the temperature curve, you only need to find the highest and lowest points of the temperature on the board. As long as the PWI of the highest and lowest points are less than 100%, the temperature of all the solder joints will be included in the specification. This isn't 100%, but the point is the get the representative points in the curve. The point temperature is the highest or lowest, so you should select a representative point from as many components (pads) as possible on the board.

 

Temperature point selection

 

For complex PCBA (large area, many components), you need to consider the following aspects:

  • The trailing edge of the leading edge vs. the dense area of the component vs. the rare area of the component needs to set the temperature measuring point.
  • The solder joint temperature of the largest component and the smallest component.
  • The body temperature of the largest and smallest components.
  • Top and bottom PCB surface temperatures.

 

 Complex PCBA

 

Thermocouple binding method

High-temperature solder

High-temperature solder provides the wetting and bonding effects of the thermocouple and pad/pin numbers, but the solder residue must be removed before use.

 

Thermocouple binding High temperature solder

 

Adhesive

Thermally conductive adhesives can be easily joined to thermocouples and used multiple times.

 

Thermocouple binding adhesive
 

solder mask tape

Solder mask tape absorbs heat, so it can only be used once. This method is usually not recommended.

 

Thermocouple binding solder mask tape

 

 

Precautions

The thermocouple wire cannot be rolled together, so it's important to make sure the contacts are made at a point. 

 rolled thermocouple wire problems

 

Ensure that the thermocouple probe for measuring air is about 2.5 cm from the leading edge of PCBA, and at least 20 cm between PCBA and the temperature recorder.

the thermocouple probe for measuring air-1