Soldering SMD parts isn’t hard task and there are many methods of doing this. Lets go through several SMD soldering methods and examples.

Method 1

For this you will need:

• Good eyes or magnifying glass. Better one and another;

• Soldering iron with small tip ~10W;

• solder wire with diameter about 0.6mm

Steps to follow:

• cut solder wire in pieces in length of element width:

• Put SMD element on circuit bord where it has to be soldered:

• Put solder wire piece next to SMD:

• While holding SMD component with pincet solder part to the board by applying iron to the solder;

• Once one end is soldered repeat same procedure with another end of SMD element:

Method 2: soldering SMD in the oven

This method is handy when you need to solder SMD packages like LQFP, TQFP64 and so on. If you don’t have special oven for soldering SMD then you can use one that you find at home. Of course take all safety precautions while working with ovens!

For this you will need:

• Mini-oven up to 250ºC. It can be cheapest oven or grill. Dont use microwave!

• Thermometer capable to measure temperature in range 20ºC – 300ºC. Possible solution to use thermocouple and multimeter:

• Soldering paste which contains 85% of solder (eg. Sn62Pb36Ag2) and 15% of flux.

• Injection needles about 1mm diameter:

Soldering in require more skils and right selection of temperatures. Soldering consists of following stages:

• Heating. Gradually increasing temperature of SMD element and solder;

• Drying. Time when Flux takes action and dries out. Duration about 1min and 30 s;

• Melting. Melting soldering paste and heating to maximal temperature about +20ºC above melting temperature of paste;

• Cooling.

This characteristics depends on soldering paste used. Look in specifications.

Find out the characteristics of your oven.

• Heat oven up to 125ºC. Curve angle should be 1-4ºC/min;

• Leave 125ºC for 1 min and 30s;

• Turn on oven and reach 210ºC;

• Turn off oven and open the door.

Read characteristic with thermocouple and then construct a chart like this:

Then you can make some conclusions from this chart:

• Heating speed. Lower speed than recommended is OK ;

• Drying stage isn’t stabile – if temperature drops too fast, add little heat to keep temperature at level. Or maybe oven has automatic heat regulation.

• Melting phase is OK;

• Cooling. Smooth drop of temperature is better. Dont try to take circuit board too fast as solder may still be soft and SMD elements may move. Leave to cool down up to 80ºC than you can take board off.

Testing oven method

Put some soldering paste on circuit board counting that paste looses about 1/3 of its volume. If applied too much you may get soldering bridges between legs, if not enough – Part legs may stay un-soldered.

When paste is applied – put SMD component on its place and put Circuit board to the center of oven. Temperature sensor should be close to board:

Then set Oven to 250ºC and wait until temperature reaches 125ºC, then turn it off for 1min and 30s. Then turn oven and reach 210ºC. You should see through window how soldering paste melts and forms a drops which fixes legs SMD elements. When 210ºC is reached – process over. Turn off oven and open the door:

After cooled – test if all contacts are well soldered.

Remember that:

• Hot air in oven oxides tracks. So after oven soldering usual soldering may be harder. One way isto clean tracks from oxide;

• melting flux produces flammable gasses which flames at 100ºC. Dont smoke while opening the door of oven;

• Soldering paste is dangerous. Ventilate the area where you are working.

Sources: www.radiokot.ru, http://cxem.net.

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This entry was posted on Wednesday, May 23rd, 2007 at 1:38 pm and is filed under Electronics Tutorial. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.