Tell me which type system you got because the design requirement changes. I know the requirements for Selective solder pallets for wave, selective solder carriers for the Vitronic Soltec MySelective 6748 & 6749 which are gantry based systems with a unique gripper assembly that picks up the edge of the PCA or carrier from the conveyor. They have PCB gripper which if designed properly will pick up carriers, otherwise if you buy the pallet only gripper then you will always have to use pallets/carriers but you save all the setup time since each carrier will have the same outline. I designed some gripper holdowns but it may be easier but more expensive to have clamps to keep SIP components and switches from tifting or tilting during solder if you use the tilt features to clear the adjacent SMT parts. The carrier edge would have a lip even with the top surface 5mm deep, 2 mm thick to simulate a board. 



The RPS, ACE and Seho Seletives moves the solder pot under the board so parts tilting is less of an issue. Of course the speed at which the board goes in and then stops could tilt some parts. The ACE Kiss 104 doesn't have the issue since you load the boards directly into the rails at the edge stop. 

 - The common considerations are: 

1.  Use a window frame type carrier to provide enough support that the  board stays flat. 

2.  Based on the thickness and tab versus scoured panels you need to access if there should be some threaded inserts in a few places where 4-40 or 6-32 hex standoffs can be used to secure the board through the mounting holes or inbetween the tabs of the panel to prevent bowed boards from lifting off the carrier.  

3. The open design provides the preheat or nitrogen blanket to preheat the board. The other reason is to provide provide a 1/2" drag out clearance for the nozzle. To reduce shorts you have to come off the last row of pins at a 45 degree angle. You don't want  to hit the center support rail nor the edge of the carrier with the nozzle. Unlike a wave pallet where all you need is 1-2 mm ( .055"0.100" clearance now you need to assure that 6mm - 12mm nozzle can drag past the component without hitting the  pallet. 

4. When you make a two-up carrier look at the drag-off clearance and determine if you need to rotatae one of the boards so you can drag in towards the edge of the carrier. It way not be possible to drag toward the narrow center strip since you can't cut away any of the center support. Also thermally you may want to put the  thermally massive parts closer together so they are heating up rather than cooling off.     

5. Soldering tips: 

   - The smaller the nozzle the hotter the solder pot temp since the solder temp at the exit of the nozzle will be less. 

   - Tin/Lead drag off speed is speed is fast 2mm sec. Lead Free the drag off speed is very slow to get the solder to snap off and not bridge, .5mm sec. 

One more thing - The vendor must assure each carrier is exactly the same from the board edge. I had programmed the first proto carrier then ordered five more and although they looked the same I had to modify the other 5. This was because initially I thought it was the repeatability of the machine as I cycled through the carriers. Then I numbered them and found what the issue was. 

 I hope this helps. 

 John Goulet Process Engineer 
----- Original Message ----- 
From: "Jim Mosher" <[log in to unmask]> 
To: [log in to unmask] 
Sent: Monday, February 23, 2009 1:36:59 PM GMT -05:00 US/Canada Eastern 
Subject: [TN] Selective Soldering design rules 

We are in the process of installing "Selective Soldering" equipment for the first 
time. Does anyone have a generic "Design Rules Guideline" for this type of 
equipment that they would be willing to share. 

Jim Mosher 

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