One of the more difficult task in assembling packs is the soldering process. Seems to me that you have that down really well. Would you explain the process you use, any trick you have to make it faster and more robust? Temp, solder type (lead or lead-free), flux or no flux. Solder on tabs vs on the cells. etc...
Leave cells connected!
Tabs are much easier to solder than cells.
1st, you must abrade solder points, dremel grinder-sander, file or even scrape with knife etc.
Flux - I use a Q-tip to spread a thin amount.
40w iron recommended (25w might work)
A hotter soldering iron transfers less heat to cells - less contact time required!
"Pre-tin" - apply solder to all solder points.
Apply a small drip of solder to tip ... allow to regain heat, apply to fluxed solder point, try 2 sec, if not good allow to cool then try 3 seconds.
(Keep a few bad cells for test soldering!)
After all contact points tinned, reapply flux.
Position for final solder apply heat till solder melds together. (Hold solder points together with chromed metal probe, small screwdriver etc.)
Test all solder connections with pick or similar.
Direct to cells is similar but usually requires slightly longer contact time, test on bad cells!
Abrade solder points
Flux all solder points
Hot soldering iron
Pretin solder points
Collapse pretined solder points onto each other
Use metal probe to position
Do many cells at once each step for all, then next step for all etc.
Practice-repetition makes perfect