How To: Solder Battery Tabs


This article covers one method of attaching wires to a bare lithium-polymer battery pouch. This could also be done using a battery spot welder, clamping, or screwing.

Warning: Lithium Ion and Lithium Polymer batteries can catch on fire if shorted, punctured or overheated.
Be careful when soldering that the battery does not become hot.
Ensure you have an appropriate fire extinguisher nearby. 

Step 1: Wire Prep

Before you solder the terminals, plan your wiring.
Where should the battery wires exit the battery? In what direction will they go, and how far? (A scale printout of the layout may help)

Strip and tin the wire ends.
Each bare end should be slightly shorter than the battery tab’s width.

Step 2: Tab Prep

Peel back one of the battery terminals.

With a small file, roughen the outer half of the battery tab.

Fold the end of the battery tab over, to create a small ‘hook’.
It should be just large enough to fit the wire in.

Put a tiny drop of flux in the hook.
You can spread it around with a piece of wire.

Step 3: Soldering

Place the wire into the hook – making sure it matches the polarity – and press it closed.
It may help to clamp a little bit of the insulation in the hook as well.

Carefully, press the soldering iron against the folded hook.
The aim here is to heat up the tab, the wire and the flux, without heating up the battery.
If the battery near the tab is warm, stop and wait 2-3 minutes before attempting again.

Run the solder into the folded hook until it begins to melt and ‘wet’ to the metal.
As soon as it seems that a good contact has been made, stop. The solder should have bonded well to both sides of the hook, and to the wire as well.

Step 4: Tidying

Roll the tab up until it is inside the battery sled.
Replace the covering tape.

Repeat for the second battery tab and wire.

Step 5: Finish Up

Once both tabs are soldered, the wires can be fixed in place with hot glue, and the area covered with a small quantity of masking tape. Complete!


Eagle: Text Silkscreen Width

Thanks to Hackvana, I’m making teeny tiny circuit boards!
No matter how good a board house’s process, there are some fundamental limits to how small things a board and the design on it can be.

A PCB is much easier to understand with a silkscreen! However, you can’t draw silkscreen lines narrower than a certain width, often about 5 mils. (Or 4 mils if you’re really lucky) So you’d better make sure none of your silkscreen is smaller, or lines will be spotty and text will be unreadable.

(Huh? What’s a mil? / One thousandth of an inch. / Okay. What’s an inch? / …)

With Eagle able to display line widths in mils, it’s not too difficult to check your lines.
What about text?
(How do I get mils? / Click on the eagle_grid_button Grid button in the upper left, and change the grid units to mils. You can change it back later)

Bad Text


Text Settings: Size: 20, Ratio: 5%. NO.

Here is the text “ISP”, and the text attributes dialog.

  • Note that font has been set to vector. Keep your text in vector mode, it will ensure that the Gerber files you output are likely to match what you see inside Eagle.
  • The grid size in these examples has been set to 10 mils
  • There are two important settings – Size and Ratio.

Size is the height of one row of text.
Ratio is the text’s line width, as a percentage of size.

  • For the above image, the line width is 5% of 20mils – only 1mil! That definitely won’t work!
  • Remember; SIZE x RATIO > 5 mils

 But I Want Small Text!

That’s fine. You’ll just need to make it thicker.


Size: 20, Ratio: 10% : 2 mil thickness. NO.

Size: 20, Ratio: 20% : 4 mil thickness

Size: 20, Ratio: 20% : 4 mil thickness. NO.

These are still a bit small…

Size: 20, Ratio: 25% : 5 mil thickness

Size: 20, Ratio: 25% : 5 mil thickness. JUST…

This one is probably juuust thick enough. But the text is only half a millimetre high!

Okay, I’ll be sensible…

Good. 50 mils (1.27mm) or larger text is probably more sensible. If size is 50, and we need at least 5 mil silkscreen, then the ratio should be higher than 10%. Easy!

Size: 50, Ratio: 5% : 2.5 mil thickness. NO.

Size: 50, Ratio: 5% : 2.5 mil thickness. NO.

Size: 50, Ratio: 10% : 5 mil thickness. JUST.

Size: 50, Ratio: 10% : 5 mil thickness. JUST.

Size: 50, Ratio: 20% : 10 mil thickness. GREAT!

Size: 50, Ratio: 20% : 10 mil thickness. GREAT! And you still need reading glasses!

One more time, graphically

Width = Size x


In Conclusion

A board house will often tell you their dimension limits, for traces, isolation, and silkscreen.
For best results, avoid the limits.

If you can make your text 10 mil thick, and the board house can manage down to 5 mil, you should have no problems.