SchmartBoard|Ez U2 Trace Exposed with Heat!
benjaminjw
Posts: 3
I noticed that the blue board material between U2 (EEPROM) pins 1 and 2 flecked away as soon as I applied a little heat to solder the first pin. It revealed a copper colored segment that runs perpendicular to the solder pads that appears to be a trace! It looks to be the same trace that runs under the pads to the via. It could be connecting pins 1 and 2 (A0 and A1) on the EEPROM, which to me is quite worry some. I don't know yet because my multimeter from university has dead batteries.
1. Has anyone else had this same problem?
2. Does anyone know if it's okay A0 and A1 are tied together? What happened to the schematic? I found it once before ordering, but now I can only find the instructions.
3. What did I do to cause such a thing? This is my second board with the same problem.
My guess is that the process used to bond the blue material doesn't work well when it has limited area to grasp hold, like the small area between the pins. The area problem coupled with a trace on the layer right below ... problems. The iron heats up the trace, the trace expands, and pop, blue non-conductive material flakes away leaving exposed trace and connection. With the first board, I thought was my fault. There was a small bridge, cold iron, and some copper braid involved. I tend to suspect myself before throwing out accusations. So, I ordered another board on my own dime. But the second board with the EXACT same problem, ... uhrmmm. I'm a professional electrical engineer with 3 years experience designing and constructing PCBs.
4. Someone from Parallax ... I'll call on Monday during technical help hours to talk.
There should be a photograph. You can see the copper shine between the pins as described.
Regards,
Frustrated
1. Has anyone else had this same problem?
2. Does anyone know if it's okay A0 and A1 are tied together? What happened to the schematic? I found it once before ordering, but now I can only find the instructions.
3. What did I do to cause such a thing? This is my second board with the same problem.
My guess is that the process used to bond the blue material doesn't work well when it has limited area to grasp hold, like the small area between the pins. The area problem coupled with a trace on the layer right below ... problems. The iron heats up the trace, the trace expands, and pop, blue non-conductive material flakes away leaving exposed trace and connection. With the first board, I thought was my fault. There was a small bridge, cold iron, and some copper braid involved. I tend to suspect myself before throwing out accusations. So, I ordered another board on my own dime. But the second board with the EXACT same problem, ... uhrmmm. I'm a professional electrical engineer with 3 years experience designing and constructing PCBs.
4. Someone from Parallax ... I'll call on Monday during technical help hours to talk.
There should be a photograph. You can see the copper shine between the pins as described.
Regards,
Frustrated
683 x 712 - 130K
Comments
That the solder mask gets removed with heat... well that happens but it is normally due to solder than flows over the trace and below the solder mask that well breaks it. Too much solder can cause that. Those are tiny pads that should be soldered with paste, little paste.
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Post Edited (Ale) : 10/3/2009 8:00:51 PM GMT
http://www.parallax.com/Portals/0/Downloads/docs/prod/boards/27150-P8X32A-Q44Schmartboard-v1.2.pdf
It indeed shows Pins 1,2,3, and 4 connected together. (A0,A1,A2 to Ground(VSS)).
I will be assembling my Schmartboard next week, (when I purchase a new soldering iron), and I will see if I can cause the solder mask to delaminate.
I believe you are OK, maybe the iron was a tad too hot?
Jim
Post Edited (Chuckz) : 10/4/2009 12:47:23 AM GMT
At home, I have a $6 (very inexpensive) 30W iron with a fairly bulky tip. Surprisingly, the problem is trying to keep it from getting cold from oxidation. I have to reapply tinner every 5 minutes or so for it to flow solder. From the picture, you can see it does okay with a steady hand. I have liquid flux in a pen form, which I would also describe as an essential tool.
My personal technique is to apply the flux, briefly (~1s) heat the joint near where the chip meets the pad, then once I can see it flow, I pull backward along the pad (~1s). The solder will flow to the hottest point; so I'm not sure how do it without heat. I tend to touch around the row of pins I'm working down, inspect the work, then retouch where it looks like it needs it. Every few pins, I will apply solder at the joint as I'm heating it. This is delicate with a large iron and large solder; as the gentleman above pointed out, a little goes a long long way. With larger gauge solder, you can see a small ball form at the end of the solder wire; when you push the solder toward the iron, you can watch it deform and start to flow toward the heat; that's just about all you need. You don't want the whole or even a substantial part of that little ball flowing onto your work; it's just too much. You're best bet if it happens by accident is to clean it up with braid if it's real bad, or to apply flux generously and spread the love down pad, using the excess pad length as a place to store the extra solder. If you have that situation, using generous flux is important because you may have Smile inside that solder joint that produces the 'cold' joint problem that will make you shake your head for hours as to why you have a stuck pin on your micro. If things go right, the flux helps pull the solder off the iron and under the chip pin. After feeling satisfied I have sufficient connectivity and the chip is in place and happy, I'll clean it all up with solvent. I also like my boards to shine, so I reapply flux, and touch around. The tip I given was to watch the top of the pin and see it flow ... then you know you have a bomber connection.
Until this board, I haven't had heat issues using this technique. Chips are remarkably tolerant to short bursts of heat from an iron. It had also been my experience that the mask was extremely durable. I knew the mask wasn't essential, but I was worried the chunk went deeper and exposed something quite bad. After a work board was finished and tested, our assembly folks would apply a conformal coating (think clear, non-conductive lacquer) over the whole of the board. That step is very difficult to undo so I wouldn't recommend for a home project. I saw a fellow engineer working hard to scratch away at the conformal coating to apply an after the fact white wire repair ... not fun. The conformal coating gives a bit of extra tolerance to moisture and grime.
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Leon
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Amateur radio callsign: G1HSM
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In metal shop, we welded and we had to weld both sides.
Some of the surface mount pins are smaller than anything I've seen. When you drop hot solder on something so small, why wouldn't the solder cook it when solder that is several hundreds of degrees hot is going to cook it anyway?
CircuitMedic is a good site with some excellent details on soldering and rework. Section 7.1.1 is about soldering basics and is really good for anyone who has not had formal IPC Solder Training. I was trained while working at HP back in 1993 to IPC 610 specs for TH and SMT soldering, so when I went through the soldering class during college in 1995, it was a breeze. It was interesting to see the various methods being used and taught. Anyhow:
CircuitMedic Soldering Procedures:
www.circuitmedic.com/guides/7-0.shtml
IPC Through Hole Solderjoint Evaluation Guide (Low-res PDF Demo Copy)
training.ipc.org/demos/pdf/drm-pth-d.pdf
IPC Hand Soldering Training Info/Videos (reduced size WMV videos; but full length!!)
www.ipctraining.org/handsoldering/index.html
On a side note (but directly related), if I had to give you one piece of advice it would be: Equipment. Spend a little extra money on your choice of a soldering now and you will be thankful down the road.
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Andrew Williams
WBA Consulting
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As I said, you *don't* drop hot solder onto it! The joint should already be at soldering temperature when the solder is applied, it melts, the solder and flux are drawn into the gap between the lead and the pad, the flux cleans the surfaces and is boiled off, leaving the solder which is allowed to cool. The whole operation only takes a second or so. Look at the soldering specification for a typical chip, and you will see that it can't be damaged if the correct procedure is adopted. A good soldering system like the Metcal unit I use helps a lot.
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Post Edited (Leon) : 10/4/2009 10:35:21 AM GMT
I had to "hardwire" the recieve pin (in my case). My soldermask was black so i couldn't "see" the traces very well. Use a multimeter to check the connections.