The problem with all of the suggestions made so far is that everyone isassuming that the pads already have solder on them.
But this is a brand-new home-made board with bare copper pads.
The first step is to tin all of the pads. Use lots of flux - gel orpaste flux works best but standard liquid flux will also work. Flood all of the pads with solder, then apply more liquid flux on top ofthe solder blobs. Hold the board vertically with the pads vertical,then use a soldering iron to draw the solder down to the ends of the padsand on to the tip. Rotate the board 90 degrees and repeat until allof the pads are tinned and cleaned. The pads should now have athin, smooth layer of solder on top of the copper.
Do a very good inspection with magnification to ensure that you don'thave any solder bridges. Then follow the (excellent) advice alreadygiven.
Hope this helps!
dwayne
PS - we used to make hundreds and hundreds of our own PCB's in the earlydays of our business. We would clean the boards mechanically with afine-grit sander followed by a 3-step chemical cleaning process. Blow the boards dry with warm air from a vacuum-cleaner motor, then feedthe boards through a GBC laminater (modified for lower temperature andhigher speed) loaded up with Dupont Riston dry-laminate film. Exposed the boards with a modified mercury-vapor expose lamp and vacuumframe, then developed the exposed boards with a soda-ash (potassiumcarbonate?) solution. Stripped the remaining laminate in acaustic-soda (sodium hydroxide) bath, rinsed, then etched in an AmmoniumPersulphate bubble etch tank.
The whole process worked very well but it just took too much time. We eventually went to CNC milling for PCB prototypes (several years),then quit that and just started using APC for prototype boards. Allof our production boards are now made in China - the quality is extremelyhigh and the cost is astonishingly low. APC still does ourprototype boards.
dwayne
At 02:29 AM 11/7/2014, Dylan Smith dyls@... [Homebrew_PCBs]wrote:
I find that it makes nodifference and trying to apply to the pads only is a frustrating waste oftime.
I just use a flux pen and draw over all the pads.
I also use kapton tape to hold the IC down for soldering rather thantrying to tack corners down. You can stick the tape to the top of the ICand hold the tape to align and once the pins are nicely all on theirpads, press the tape down onto the PCB. Then just drag solder the twoexposed sides, remove the tape, and solder the remaining twosides.
On 07/11/2014 09:12, Phil Quintonphil.quinton@... [Homebrew_PCBs] wrote:
James,
- Thanks for the reply.
- Do I need to keep the flux just on the pads ( appears fiddly ), orcan I just apply to the whole of the pads as a "square" offlux?
- Am I correct in thinking that the latter would end up with moresolder bridges due to the solder flowing between the pins due to the fluxbeing between the pins?
--
Dwayne Reid <dwayner@...>
Trinity Electronics Systems Ltd Edmonton, AB,CANADA
(780) 489-3199voice (780)487-6397 fax
Custom Electronics Design and Manufacturing