caveduck
semi old rocketeer
- Joined
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Something I've been working on incrementally this year amongst all the machining projects - assembling Eggtimer board kits efficiently and repeatably.
This is a 3D printed fixture with an insert that has registration pins that fit the Quantum board mounting holes, and is set up so that the top of the board is flush with the top of the main red fixture. It's used for paste solder application with OSH stainless steel templates. The top and bottom side templates are tape-hinged on either side. Most of the printed blue insert is cut out so that boards that already have one side populated can be flipped over to have paste applied to the other side. The screws that hold the insert to the red table are countersunk flush. I'm planning making another insert to hold Quantum boards, and another whole fixture for the much larger Protons and TRS's. I'll get this up on Thingiverse after the AirFest crunch.
I'm using two kinds of solder with different melting points to do the dual-sided reflow, which is done with a mechanical-controls toaster oven and an Arduino based reflow controller I got off of Kickstarter a few years back. On the bottom side I'm using regular SnPb (217C) and on the top side it's SnBi (137C). The bottom gets done first with the higher temp SnPb. Then the top side can be done without affecting the bottom side since the SnBi cycle never reaches the melting point of the SnPb. The pre-soldered chip on the other side will not fall off, it's not heavy enough to defeat the surface tension holding it on. Yes, the WiFi module is getting reflowed onto the board - I just run a line of solder down each row of pads and put a couple of resistor leads in diagonal corners. After the board tests good they get epoxied down since the module has some mass.
[Edit: forgot to mention I'm using some 1.0 mil kapton tape under the WiFi module to protect the vias under it. Much thinner than the suggested masking tape (less likely to make the pads not bond) and more compatible with reflow temperatures.]
For batch assembling I be sure to put a Brother label on the WiFi chip with the access key before assembly. It survives the reflow run just fine. Through-hole parts get hand-soldered afterward.
This is a 3D printed fixture with an insert that has registration pins that fit the Quantum board mounting holes, and is set up so that the top of the board is flush with the top of the main red fixture. It's used for paste solder application with OSH stainless steel templates. The top and bottom side templates are tape-hinged on either side. Most of the printed blue insert is cut out so that boards that already have one side populated can be flipped over to have paste applied to the other side. The screws that hold the insert to the red table are countersunk flush. I'm planning making another insert to hold Quantum boards, and another whole fixture for the much larger Protons and TRS's. I'll get this up on Thingiverse after the AirFest crunch.
I'm using two kinds of solder with different melting points to do the dual-sided reflow, which is done with a mechanical-controls toaster oven and an Arduino based reflow controller I got off of Kickstarter a few years back. On the bottom side I'm using regular SnPb (217C) and on the top side it's SnBi (137C). The bottom gets done first with the higher temp SnPb. Then the top side can be done without affecting the bottom side since the SnBi cycle never reaches the melting point of the SnPb. The pre-soldered chip on the other side will not fall off, it's not heavy enough to defeat the surface tension holding it on. Yes, the WiFi module is getting reflowed onto the board - I just run a line of solder down each row of pads and put a couple of resistor leads in diagonal corners. After the board tests good they get epoxied down since the module has some mass.
[Edit: forgot to mention I'm using some 1.0 mil kapton tape under the WiFi module to protect the vias under it. Much thinner than the suggested masking tape (less likely to make the pads not bond) and more compatible with reflow temperatures.]
For batch assembling I be sure to put a Brother label on the WiFi chip with the access key before assembly. It survives the reflow run just fine. Through-hole parts get hand-soldered afterward.
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