Alternative solder and fragile part - Page 1
Forum section: electronics / beginners

author: palindrome
author_rank: Contributor
timestamp: December 09, 2022, 03:55:14 pm
content: Hi,I have this problem where I need to solder a fragile part (THT polystyrene capacitor) to a 6 layer board with quite large ground planes.It's doable, but my soldering iron is struggling with this and I am worried that I may get the capacitor damaged (so far it has not happened).So I've been thinking maybe I could use a solder with lower melting point, like made of Indium for that specific part?This is a commercial product so I don't know if that material can be used? The packaging on the solder says it's RoHS compliant.Alternatively should I get as large tip as possible and more powerful iron?I am using Hakko FX-951.Cheers!

author: Ian.M
author_rank: Super Contributor
timestamp: December 09, 2022, 04:10:28 pm
content: Design problem - the footprint for the cap should have had long enough, thin enough thermal reliefs on its ground side to permit quick easy soldering.If you heatsink the lead between the cap and the board with locking metal forceps and use the biggest hoof bit you can get to fit your iron, you shouldn't have any problems.

author: KaneTW
author_rank: Frequent Contributor
timestamp: December 09, 2022, 04:28:26 pm
content: Preheat the board.

author: Ian.M
author_rank: Super Contributor
timestamp: December 09, 2022, 04:55:59 pm
content: If you preheat, do so very very carefully. Polystyrene capacitors have a max. working temperature of 85°C and start melting at only 100°C. To avoid damaging the capacitor when soldering to a pre-heated board, you'd need to insert the capacitor after preheating, probably with a slip of corrugated card under it for thermal insulation and maybe even use pre-chilled heatsinking forceps on both leads to keep the lead temperature at the capacitor body down long enough for the board to cool enough for the capacitor to be safe

author: Fraser
author_rank: Super Contributor
timestamp: December 09, 2022, 05:52:30 pm
content: Another option is to reduce the thermal heat sinking effect by soldering a short length of nice quality TCW or, better still, Silver plated wire, into the PCB to act as mounting posts. Then attach the polystyrene capacitors to these mounting posts by winding a couple of turns of their leads around each post. Solder the capacitors leads to the mounting posts as quickly as you can. Use the largest diameter wire that will fit through the PCB holes to act as the rigid mounting posts. If done correctly, it will be a very professional job to look at and is far better than exposing the capacitor to the heat that may be needed to solder into a poorly designed feed through hole. Heat shunting the capacitor lead has already been mentioned and is another very good option.Good luck with the jobFraser

author: TimFox
author_rank: Super Contributor
timestamp: December 09, 2022, 06:28:46 pm
content: Back around 1983, we designed an ADC board that used polystyrene capacitors (for sample-holds) on a 4-layer THT board.We used proper thermal reliefs on the pads for the polystyrene capacitors, but needed to have the capacitors hand-soldered (after everything else was wave-soldered) due to the low service temperature on the PS part.The board assembly house had no problem with this, but I don't know what they used for hand-soldering irons.

author: palindrome
author_rank: Contributor
timestamp: December 09, 2022, 11:03:25 pm
content: Thank you so much for ideas!I feel stupid, I just realised I can edit thermal reliefs on those pads!

author: Watth
author_rank: Frequent Contributor
timestamp: January 24, 2023, 08:05:26 pm
content: Would it be possible to solder a 2 pins socket then insert the capacitor?

author: jonpaul
author_rank: Super Contributor
timestamp: January 24, 2023, 08:08:20 pm
content: needle nose pliers heatsink lead ,Metcal iron, 63/37 tin/lead eutetic solder.Jon

author: bidrohini
author_rank: Regular Contributor
timestamp: January 27, 2023, 07:46:05 am
content: Using a solder with a lower melting point, such as one made of indium, may help to reduce the risk of damaging the fragile THT polystyrene capacitor during the soldering process. However, it is important to ensure that the solder you use is RoHS compliant and suitable for use in a commercial product.An alternative solution would be to use a larger tip and a more powerful soldering iron. The Hakko FX-951 has a temperature range from 240°C to 540°C, a larger tip may help to distribute the heat more evenly and reduce the risk of damage to the capacitor.It's also good practice to preheat the PCB before soldering, it will help the heat to dissipate evenly and reduce the risk of damaging the part.However, it's always a good idea to consult the manufacturer's recommendations for soldering these types of parts and to use the correct soldering techniques and equipment to minimize the risk of damage.