The SMT Flow When Production A Bluetooth Module

- May 14, 2020-

SMT

Furnace temperature curve

image

Preheating zone A

The main purpose of the preheating zone is to heat the motherboard and components to 120 ~ 150 ℃. This promotes the rapid evaporation of the solvent and reduces the thermal shock to the components. It is recommended to increase the temperature to 150 ℃ at a rate of 0.5 ~ 2 ℃ / s. If the heating rate is too fast, it is easy to produce tin balls, which is caused by the vaporized solvent splashing, and will also cause the wick phenomenon, component deflection, etc.

Preheating zone B

At this stage, it is necessary to activate the flux and ensure that the temperature distribution on the board is uniform. The hot air reflow furnace commonly used today is much more uniform than the infrared furnace several years ago, so a linear heating curve can be used. Also refer to the board size, density and furnace efficiency. It is recommended to bake at 150 ℃ to 210 ℃ for about 60 to 120 seconds

Preheating zone C (Select)

In order to solve the problem of standing monument, it can be kept in the baking zone at 210 ~ 217 ℃ for 20 to 30 seconds.

Reflow zone D

The curve shown in the figure is made for Sn / Ag3.0 / Cu0.5 alloy, which can be used as a reference for other alloys. It is necessary to adjust the curve according to the requirements of the specific process. The recommended peak temperature (Tp) is between 230 and 250 ℃, and the time above 217 ℃ is between 30 and 90 seconds.

Cooling zone E

The recommended cooling rate is less than 4 ℃ / s to allow the board to cool quickly and solidify the solder joints to minimize the intermetallic compound layer. It is also helpful for hand-holding, and at the same time avoids the flux volatiles entering the workshop. The fast cooling speed also helps to produce a small and compact particle structure. The solder joints with large particle structure caused by the slower cooling rate have relatively poor reliability.

Reflow soldering

When the PCBA of the mounted module is passed through the furnace, please strictly require the PCBA to pass the furnace through the track, and it is strictly forbidden to pass the reflow furnace through the grille. Because there are BGA devices on the module, the shake of the grille will easily lead to a high ratio of sticky welding of BGA pins.

Reflow soldering process design, such as when making furnace fixtures, should avoid interference designs that cause any device offset on the module.

Wave soldering of PCBA with module

For PCBA with modules attached, if wave soldering is required due to process requirements, please provide special protection to the module to prevent abnormal soldering short circuit or other unpredictable hidden troubles caused by tin splash during wave soldering.

It is not recommended to use PCBA with modules for wave soldering process. Please consider soldering the modules manually after wave soldering.

Precautions

The recommended solder paste is no clean flux

Do not immerse the module in the flux tank

Do not use excessive flux or solder paste to prevent short circuit

It is forbidden to pass the Bluetooth module twice, nor to reverse the module (with the chip facing down)

When passing the furnace, try to ensure that the module moves forward smoothly, and slight vibration may cause virtual soldering or short circuit of the BGA chip.