Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Solder woes

David Harper


Solder woes | 6 August, 2000

The company I work has been assembling this particular board for several years now, and one thing has always remained constant. Bad Soldering. The board is a double sided board, the solder side has about 250 1206 caps & resistors and Sot-23 transistors and diodes. the component side has afew dozen through hole parts.

The process in which we assemble this board as is follows: the surface mount side is assembled first using adhesive via a dispenser.. then the through hole goes in.. and then it is soldered via a solder machine . The problem is.. the surface mount parts do not solder well.. balled solder or no solder at all. esp on the SOT-23 leads.. and the rework and touch up is a pain in the neck.

Does any one have any insight into this problem? the flux we are using is ft100 aqua flux. we know it is not the solder machine, we took a sample to a place with a wave solder machine and the soldering was the same. The adhesive is not on the pad so it's not that.. the only thing I can think of, this the leads on the SOT-23 parts are to small??? for the solder to stick to... or the boards themselves are contaminated somehow.

Any insight would be a great help.


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Re: Solder woes | 7 August, 2000


What type of wave solder are you using? How are the t-sots oriented relative to the direction of travel? You will get the best results with them oriented with the length of the body parallel to the direction of travel. You want the leads oriented so that none of them are shadowed in the wave. Also, we typically increase the pad dimensions to those similar to an 0805 chip. We do the same for the diodes. Also, we used to run a similar board on an old econopak plus with the turbulent wave. We still had marginal results. We upgraded to E-vert's rotary chip wave and have had excellent results ever since.

Hope this helps John S

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Bob Willis


Re: Solder woes | 10 August, 2000

Solder skips on SOT23 parts is the most common issue when soldering surface mount designs. The two most common causes are the wave height too low or there is too much gassing of the flux as it contacts and seperates the wave.

Stck some parts on your glass plate and run it throug the wave and see what happens.

As stated the real reason for a double wave is to solder SOT23's they should have called the original double wave a SOT Buster ?

Bob Willis

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Re: Solder woes | 10 August, 2000

thanks very much for the info John and Bob, and I'll see what happens next time I run them through...I'll keep the you and the forum posted


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Jade Series Selective Soldering Machines

Encapsulation Dispensing, Dam and Fill, Glob Top, CSOB