Reflow oven soldering problem.

[gauravkothari23]

Hi all,
I have made a small reflow oven to solder my SMD components. I am using Sn63/Pb37 leaded solder paste. And maintaining the temperature of 220 degree Celsius. My problem is my half of the components do not get solder properly. The components sometimes gets lifts up from one side but gets properly soldered from other side(image attached) and also it gets moved away from the pad(image attached).
I have also checked for any types of vibrations when the oven is ON, which can make the components move away from the pad, but there's nothing like that. Can you please help me out of this.

 

[Externet]

Make very sure the solder paste has not absorbed humidity while waiting for use, as a in its container left long uncapped.

Microdroplets of absorbed moisture explode as steam under oven temperatures moving anything.
Check with known fresh solder paste that its container has never been open/exposed to humid air to confirm your case.

 

[gauravkothari23]

Thanks.... I have brought a new Solder paste which was completely sealed and never exposed to open air.
but when i apply the solder paste on PCB using my aluminium stencil, the solder paste is anyhow going to be exposed to open air till i place all my components. it takes atleast 10 to 15 minutes for me to place all my components on PCB. can this create any problem.

 

[Externet]

The exposure time to moist air has to be more than 10 minutes to become a problem, or the electronics industry would be in a huge permanent headache. In my opinion, do not dream of leaving the paste applied hours or overnight for next day reflow.

How long I cannot tell, it has to depend on how humid the room is. Some integrated circuits are also prone to absorb moisture into their packaging! and are sold in sealed pouches with moisture exposure monitors* and dessicant, keeping unused ones in nitrogen dehumidifier cabinets**.

* ----> http://i.stack.imgur.com/dSxYF.jpg
----> http://supplychainminded.com/moisture-sensitive-components-need-sensible-handling/
----> http://www.mcdry.asia/html/main1.html
----> http://img.deusm.com/ebnonline/2013/11/269960/Allen-EBN-moisture-sensitive-parts.jpeg
** ----> http://www.mcdry.eu/english/html/main.html

Come back after trying a known 'dry' solder paste comparing results.

 

[KlausST]

Hi,

From your description ... maybe the preheat phase is too short.
In the solder paste there is flux and something like "thinner".
The flux needs some time at around 100°C to do it's job.
At the same time the thinner vaporizes.

I recommend to read some documents about reflow soldering teperature profile.

Also buy some color changing temperature test stickers to check PCB temperature. Usually you do need them only for the first tests.

Klaus