Odd question - SMD board heater - Page 1
Forum section: electronics / projects

author: jduncan
author_rank: Regular Contributor
timestamp: June 14, 2025, 11:49:37 am
content: So I'm brainstorming ideas to prototype something like an impulse sealer, but with a fairly large (~200x100mm) area and a complicated sealing pattern, with curving seal lines a few mm wide. Limiting heat outside the seal zone is also important - I've experimented with machined aluminum blocks, but its tough to control heat spread.I'm thinking now about using a PCB with exposed copper tracks on the bottom side as my sealing elements. Vias to the top side, and SMD resistors or something else as the heaters.What's my best option for a small, cheap, heat source? And how best to get heated directed into the traces on the bottom?At first I thought I'd use the terminal pad for heat transfer, but looking resistor datasheets, it seems the resistive film is on the top surface. Maybe I do best to flip them upside down, and straddle a bare copper pad?Or maybe some kind of mosfet with a heatsink pad would do a better job?

author: Psi
author_rank: Super Contributor
timestamp: June 14, 2025, 11:57:31 am
content: Could you use the tracks themselves as heaters. Its the best way to get the heat exactly where you want it.Depending on the temp needed you may need to use a high temp PCB.

author: pcprogrammer
author_rank: Super Contributor
timestamp: June 14, 2025, 12:45:04 pm
content: There are PCB reflow plates based on this principle, but durability is an issue. Search the net for "pcb base reflow plate".For instance:https://www.hackster.io/john-bradnam/pcb-reflow-hot-plate-ad6726You can also use an aluminum PCB for better heat spreading, but not sure it that is what you need.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 14, 2025, 01:13:59 pm
content: Problem with PCB is likely to be FR4 is reasonably thermally conductive, and may deteriorate at required temps - maybe a PCB with slots cut around the tracesAnother option might be a stainless stencil with insulated backing and non-stick coating on the top

author: Fraser
author_rank: Super Contributor
timestamp: June 14, 2025, 02:21:48 pm
content: There is a good reason for commercial heat sealers using simple nichrome wire and foil heaters that may be easily replaced when they fail. Nichrome is perfect for high temperature generation and it should be used with a suitable Teflon tape. A heater may be shaped on a former and then contained in heat resistant Teflon tape. The tape prevents sticking of the sealed material to the heater and this can be important.Finally, you have the safety aspects of a high temperature heater to consider. Unsafe heater deigns can lead to fire and liability claims. This is why I recommend taking a lead on the heater design from commercial designs that already overcame the development challenges that you will otherwise face. Nichrome wire and flat foil is wonderful stuff that is easily used as a heater but there are other metals that may be used and custom foil heaters may be manufactured in a fire resistant silicone coated foil format.Fraser

author: wraper
author_rank: Unknown
timestamp: June 14, 2025, 02:35:54 pm
content: I think you could laser cut a nichrome sheet, with areas that don't need sealing but used as electrical conductors made several times wider than heating areas. Thus preventing them from doing unwanted sealing as they won't get hot enough.

author: ajb
author_rank: Super Contributor
timestamp: June 14, 2025, 06:38:28 pm
content: Quote from: Fraser on June 14, 2025, 02:21:48 pmThe point about impulse sealers is a good one -- the other factor that makes them effective is the very low thermal mass of the heater. This may well be the source of the heat spread issues with machined aluminum plates mentioned by the OP: the longer it takes to get the heater up to temperature, the more time you have for that heat to spread through the target material, which reduces the amount of control you have over the sealing process.I think there's a similar problem with using resistors as the heating elements and trying to conduct the heat through to the copper -- the rate of heat flow will tend to be poor, which will also slow the temp rise on the sealing side.Quote from: wraper on June 14, 2025, 02:35:54 pmPhotoetching may be a better bet, depending on the geometry and how accurate it needs to be. Laser cutting long thin shapes accurately can be challenging due to the localized heating causing geometric distortion. There are strategies to limit this, like leaving lots of supporting tabs or staggering the cuts between sides, but a strategy like photoetching that doesn't involve heat at all may be a better choice.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: June 15, 2025, 01:55:44 pm
content: Good Morning Jduncan, What temperature are you hoping to achieve