Migrating from P1 to P2
kolyur
Posts: 43
Hi all,
Back in 2011 I developed a controller PCB for a customer using a P1 chip. We are still manufacturing this product so needless to say I appreciate the longevity of the P1. It's a relatively low volume product so the PCB has always been hand assembled with through hole components including the DIP version of the P1.
I'm working on some updates to the design that will require moving to the P2 chip, mainly due to program size and I/O count. I'm trying to assess the changes that will be required in my production process. I have hand soldered SMT packages similar to the TQFP-100 in the past (ugh), but I don't have much experience with other techniques. My thought is to convert a toaster oven using a Controleo or similar, and get stencils with my next PCB order so I can apply the solder paste and do proper reflow.
Just wanted to get some thoughts from others who are doing this already. Are many of you doing small batch reflow with the P2 chip? Any tips or things I should watch out for? I can get a hot air handpiece for my Pace setup... is there any value in that for assembly or just rework?
Any suggestions are very much appreciated!
Comments
I do the Propeller programming for JonyJib. The owner, John (Huffman) assembles his own boards and uses through-hole. He recently release a P2-based product that uses the P2 Edge in a socket and continues to use TH for the rest of the board. That is certainly an option. There are a few forum members that have made custom P2 boards, so that is possible.
I think @Rayman has done home reflow for his custom P2 board. Perhaps he'll chime in.
You and I face similar choices.
FWIW, the P2 can be hand soldered using a preheater and a hot air pencil reflowing ChipQuik paste. Works nice! I prefer the ChipQuik 63/37 leaded solder paste and Kester RMA flux followed by a dip in the ultrasonic cleaner. The boards look awesome. On occasion you may get a bridge. If so, Gootwick is your friend. You absolutely need a video microscope for inspection. Get a cheap one. They work great. As to air pencils, I have both the Zephyrtronics and a X-Tronics. Both work well and are recommended. I was using the converted toaster oven, but honestly I prefer the air pencil with preheat approach. YMMV.
This is my approach
because I want to MEFA (make electronics fixable again) 
I replace 30+ year-old CNC systems, usually because the HMI (screen/keyboard/touchscreen) has died. The control boards are like new and the majority of the chips are socketed.
A "care package" consisting of a spare P2-Edge and a handful of the garden-variety, socketed buffer devices is easily justifiable.
Contrast this with a $2,500 PLC that dies on a weekend (24/7 production), wait until Monday morning and hope that your supplier still carries that particular model and then there's the problem of loading the program
Craig
I guess we're all facing the same choices for development of a P2 based board.
The Edge module is probably the easiest way. There's even a through hole version of the connector, but I used the SMT version with stencil and paste.
That is a pretty good solution, but I'm not 100% sure I'm OK with it for an important device. Kind of on the fence about which way to go...
There was a time when people here considered hand soldering the ground pad by making big vias under the chip, but I don't think anybody actually did that.
I've also made several boards using the P2 chip with stencil and paste. If you don't have something to place the P2 chip precisely on the paste with, be prepared with some solder wick to clean up bridges. That can be a pain. I usually add more solder to the bridge and then wick it all up. If you're very unluckly the P2 may rotate on you and then you do need the air gun and patience to move it.
@ManAtWork also sells a P2 module, I believe.
My other choice might be to just use the P2 Eval, the main thing I'm working toward fits in a big box with plenty of room.
But, I'll probably use my own board. It can't go to 352 MHz, like the P2 Eval, but it does 250 MHz just fine.
Also, I'm doing all digital. The Edge or Eval are probably much better if doing analog.
Thanks to all of you, this is great information. I had considered the P2 Edge board initially but my reservations were (a) cost and (b) longevity. Thinking back to my history with the P1, it seems like Parallax has released and discontinued a number of boards with the P1, but the chip itself was always available. That made me a bit nervous about the P2 Edge. Can we expect it to be around long term? I suppose that if it does get discontinued, it's likely that Parallax or a community member would start manufacturing something similar to fill the gap. The cost also seemed excessive at first but it would free me up from having to provide and install a lot of support components, and most importantly would eliminate the SMT learning curve.
I will admit that the P2 Edge is sounding more and more appealing. The fact that a through hole socket is available is like icing on the cake. I feel like a bit of a dinosaur sometimes, sitting here soldering my through hole boards, but at the volumes I work with it just makes the most sense. Sometimes we have damaged boards that come back and rework is super easy. It's nice to hear that I'm not the only one still doing THT.
I think the Edge will be around for a long time as there are people deploying it in commercial apps and Parallax would not want to be disruptive to those customers.
Long life availabilty is indeed the plan on P2 Edge, just like the FLiP and BASIC Stamp modules.
I almost complained that they weren't available at Digikey but it was just a matter of looking in the right place. There is a straight and right-angle option.
Craig
A couple of questions about the right-angle connector 450-00308:
3.5 mm
With the right-angle socket, put a couple mounting holes in your PCB and use board spacers or standoffs. The Edge module could sit over other components on your base PCB to save space.
With the vertical socket, (or with the right-angle should it overhang your PCB), then add some standoffs to your case at an appropriate point.