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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
I'm trying to make a 10x scope probe that is capable of dealing with
slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. Thank you. al |
#2
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
On Sep 25, 7:02*pm, mickgeyver wrote:
I'm trying to make a 10x scope probe that is capable of dealing with slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. *I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. Thank you. al dang G00gle..... "http://picasaweb.google.com/UncleAltheKiddiesPal/Probe#" |
#3
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
mickgeyver wrote: On Sep 25, 7:02 pm, mickgeyver wrote: I'm trying to make a 10x scope probe that is capable of dealing with slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. Thank you. al dang G00gle..... "http://picasaweb.google.com/UncleAltheKiddiesPal/Probe#" It looks like you used cheap phenolic PCB materials. Fiberglass is a lot more stable. -- You can't have a sense of humor, if you have no sense! |
#4
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
On Fri, 25 Sep 2009 16:02:55 -0700 (PDT), mickgeyver
wrote: I'm trying to make a 10x scope probe that is capable of dealing with slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. Thank you. al Use 0.032" media. Bake under a flat press upon receipt of the bare boards. Hand assemble... no wave solder, no IR oven. Those are the only techniques that yield 100% positive results. Any automated process will certainly have a poorer prime pass yield. That is, unless the PCB maker was real good at stress relief during the making of the boards. |
#5
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
On Sep 25, 8:35*pm, Archimedes' Lever
wrote: On Fri, 25 Sep 2009 16:02:55 -0700 (PDT), mickgeyver wrote: I'm trying to make a 10x scope probe that is capable of dealing with slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. *I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. Thank you. al * Use 0.032" media. *Bake under a flat press upon receipt of the bare boards. I'll try to find thicker stock. Like Joerg there is no expense money available for this project so I gotta use whatever is available. There is a connector on the other end that I'm using to leech power from the scope so I have limitations here. * Hand assemble... *no wave solder, no IR oven. Done that. Perhaps if I make a frame to clamp it flat during assembly. * Those are the only techniques that yield 100% positive results. * Any automated process will certainly have a poorer prime pass yield. * That is, unless the PCB maker was real good at stress relief during the making of the boards. I'm the PCB maker all contained in house with a mill machine. |
#6
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
On Sat, 26 Sep 2009 06:34:12 -0700 (PDT), mickgeyver
wrote: * Hand assemble... *no wave solder, no IR oven. Done that. Perhaps if I make a frame to clamp it flat during assembly. Then your dwell time on each solder joint is way too high. Try 1/20th gram per joint, not the half gram per joint the picture appears to show. You know... NASA soldering specs. As little solder as is possible and perform the operation quickly. What I saw looked like several time the amount needed in the dip chip. Even the connector was huge and blobby on the solder joints. The builder does not need to flood those pins with solder. The solder only needs to be between the pin and the board ala SMD soldering. FILLET not BLOB. The soldering iron should also be at 600° F, NOT 800° F. If you are having wetting problems due to age of the leads of your parts or such, you may need to try different solders to see if a different flux choice might yield a good solder joint faster than your current choice. RMA is harder to clean (hot alcohol bath) but it does make a good, well wetted solder joint faster in some instances. I am not sure which flux choices are the most active these days. It has been a long time since I did production level soldering, and we currently use odd technology since we get exempted from RoHS compliance. |
#7
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
On Fri, 25 Sep 2009 16:02:55 -0700 (PDT), mickgeyver
wrote: I'm trying to make a 10x scope probe that is capable of dealing with slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. http://picasaweb.google.com/UncleAltheKiddiesPal/Probe?feat=directlink Is that a Polysulfone board? With 0.020 inch anything, and all that copper, it's going to warp no matter what you do. Any differential heating, on one side of the board, is going to cause the board to bend. I ran into the same problem years ago with wave and hand solder in thin boards. Going to thicker boards, with some kind of stiffener was not an option because of weight limitations. However, you apparently don't have that problem. Try 0.032 or 0.0625 boards, keep the heating to a minimum, and it might work. I think you might be entertained by what happens to just the board, without any components. Clamp one end of the board into a vice. Heat one side of the board with a hot air gun or soldering iron. The copper will expand, causing the board to warp. In other words, the large copper areas are what's causing the warping. You can somewhat minimize the effect by pre-heating and post-heating the board. We found that freon vapor reflow soldering produced absolutely flat boards. That because the entire board was heated evenly, and cooled down evenly and slowly. Heat one side of the board more than the other (i.e. differential heating) and it's going to warp unless you're very careful on cooling it down evenly. When we went to surface mount devices, small traces, and 0.5 oz Cu traces, the warping was gone. 0.020 is thin enough that the board can be straightened by the mounting arrangement. Instead of the round brass tube, it might be possible to use an aluminum tube, with two grooves milled into the inside diameter. Your current board does not have enough unused area along the lengthwise edges to do this, but it can be expanded somewhat. This also has the advantage of providing a nifty ground connection to the case. However, inside milling is expensive. A square aluminum extrusion is possible, but even more expensive. Good luck. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
#8
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
On Sep 25, 11:41*pm, Jeff Liebermann wrote:
On Fri, 25 Sep 2009 16:02:55 -0700 (PDT), mickgeyver wrote: I'm trying to make a 10x scope probe that is capable of dealing with slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. *I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. http://picasaweb.google.com/UncleAltheKiddiesPal/Probe?feat=directlink Is that a Polysulfone board? No. Just a scrap of fiberglass board from long ago. I have some Rogers flex board, but the surface appeared too rough to get good results on my PCB mill. With 0.020 inch anything, and all that copper, it's going to warp no matter what you do. *Any differential heating, on one side of the board, is going to cause the board to bend. * I ran into the same problem years ago with wave and hand solder in thin boards. *Going to thicker boards, with some kind of stiffener was not an option because of weight limitations. *However, you apparently don't have that problem. *Try 0.032 or 0.0625 boards, keep the heating to a minimum, and it might work. Can't go too thick here as I'm leeching power from a Tek P6204 probe cable. I think you might be entertained by what happens to just the board, without any components. *Clamp one end of the board into a vice. *Heat one side of the board with a hot air gun or soldering iron. *The copper will expand, causing the board to warp. *In other words, the large copper areas are what's causing the warping. I'll try that just for grins. Never thought of thin PCB material as a bi-metalic thermostat element. You can somewhat minimize the effect by pre-heating and post-heating the board. *We found that freon vapor reflow soldering produced absolutely flat boards. *That because the entire board was heated evenly, and cooled down evenly and slowly. *Heat one side of the board more than the other (i.e. differential heating) and it's going to warp unless you're very careful on cooling it down evenly. *When we went to surface mount devices, small traces, and 0.5 oz Cu traces, the warping was gone. 0.020 is thin enough that the board can be straightened by the mounting arrangement. *Instead of the round brass tube, it might be possible to use an aluminum tube, with two grooves milled into the inside diameter. *Your current board does not have enough unused area along the lengthwise edges to do this, but it can be expanded somewhat. *This also has the advantage of providing a nifty ground connection to the case. *However, inside milling is expensive. *A square aluminum extrusion is possible, but even more expensive. I was concerned that too much bending would crack some of the components giving me problems later on. I don't want this to get too big as it lets me attach this unit to a probe manipulator to use under a microscope to hit those tiny nodes. Like I've stated before.... I'm leeching power from the business end of a TEK P6204 probe. The 3/8 brass tube mates up nicely with the Tek probe cable strain relief at the probe end. I'll post more photo's of the other end for the groups viewing pleasure. Good luck. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 #http://802.11junk.com* * * * * * * #http://www.LearnByDestroying.com* * * * * * * AE6KS |
#9
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
On Sat, 26 Sep 2009 06:52:30 -0700 (PDT), mickgeyver
wrote: Can't go too thick here as I'm leeching power from a Tek P6204 probe cable. Ok. I just noticed that the backlighting LCD inverter in a typical laptop is constructed similarly to your prototype. Very thin G10 board, 10mm wide, and all the parts on one side. To make matters worse, a big routed hole in the middle for the xformer. Huge copper ground plane on one side of the board. Yet, all the boards in my collection are quite straight. That demonstrates that it can be done. I'm not sure what you're doing that's wrong, but I agree with others that suggest you're using far to much solder and heat. Smaller parts, less solder, and less heat will help. Incidentally, when I say less heat, I don't mean less temperature. I use the hottest iron tip I can get away with, and work fast. That minimizes the energy transfered to the solder joint and therefore reduces the heat affected zone. I was concerned that too much bending would crack some of the components giving me problems later on. PCB warping will certainly cause problems. It really depends on the physical size of the components. Parts with flexible leads (xsistors, IC's) are not much of a problem because the leads absorb the flex. Parts that are soldered directly to the board, will either crack, or rip the traces off the board. If you can't fix the flexing problem, switch to a flexible PCB design and apply an insulating stiffener board on the circuit side. It can't be prototyped with at PCB router, but at some point, you're going to have to commit to a PCB layout. Might as well do it early. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#10
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
In article ,
Jeff Liebermann wrote: Yet, all the boards in my collection are quite straight. That demonstrates that it can be done. I'm not sure what you're doing that's wrong, but I agree with others that suggest you're using far to much solder and heat. Smaller parts, less solder, and less heat will help. Incidentally, when I say less heat, I don't mean less temperature. I use the hottest iron tip I can get away with, and work fast. That minimizes the energy transfered to the solder joint and therefore reduces the heat affected zone. I think one problem is that this is a home made board. The holes are likely too large for the components (because most people don't have very small drills on hand or even the drill chuck to hold them) and obviously they aren't plated through. That can make it necessary to glob on the solder. As far as temperature, I agree with you. I've never found a need to solder anything at less than 800F. Smaller parts just require shorter dwell time. I have no idea why the OP is using such thin stock, though. It looks like he'd have room for something as robust as .050". |
#11
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
On Sun, 27 Sep 2009 11:59:32 -0700, Smitty Two
wrote: In article , Jeff Liebermann wrote: Yet, all the boards in my collection are quite straight. That demonstrates that it can be done. I'm not sure what you're doing that's wrong, but I agree with others that suggest you're using far to much solder and heat. Smaller parts, less solder, and less heat will help. Incidentally, when I say less heat, I don't mean less temperature. I use the hottest iron tip I can get away with, and work fast. That minimizes the energy transfered to the solder joint and therefore reduces the heat affected zone. I think one problem is that this is a home made board. The holes are likely too large for the components (because most people don't have very small drills on hand or even the drill chuck to hold them) and obviously they aren't plated through. That can make it necessary to glob on the solder. Good observation. The lead size, and hole size and even the annular ring width all inter-relate if one is to produce minimalist 'NASA' style soldering results. As far as temperature, I agree with you. I've never found a need to solder anything at less than 800F. Smaller parts just require shorter dwell time. This one is off the mark. Perhaps you meant "at MORE than 800°F" That would certainly be an upper max for me, and it is quite easy to solder at much lower temperatures. Well over a 100 degree differential, and that is significant. I have no idea why the OP is using such thin stock, though. It looks like he'd have room for something as robust as .050". He could make little SMD circuits that he places on Silica wafers, and then place those wafers on the substrate with epoxy, and wire the sections together. I used to use 0.020 wafers up to 2 x 2 inches to make little smd proto circuits on. I have glued smd parts on, and hand wired point-to-point the nodes between the parts. I have also 'dead bug' glued thru-hole 8 pin dips onto it and wired those nodes with hook-up wire. The leads were shortened, of course. That sounds like a good proto build solution, but to make a production run would require a different decision. |
#12
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
mickgeyver wrote:
I'm trying to make a 10x scope probe that is capable of dealing with slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. Thank you. al Tin the tracks with hot solder on the side outside the curve, as it cools and contracts it will straighten the board. |
#13
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
I'd probably try a couple of methods which may or may not help. In welding,
the welds are often alternated from one side to the other, as the cooling phase causes distortion. The alternating method minimizes distortion. Another method that I'd consider, would be to raise some of the axial-lead components slightly above the board surface, where space permits. A shim of file folder material may be enough to leave a small gap, so the lead positions wouldn't be so rigid. (the shim removed after the solder cools). Jumper wires (soldered with a shim underneath them, or a slight hump) placed laterally where they wouldn't interfere with other components or signals, may add some flexibility to the overall assembly. -- Cheers, WB .............. "mickgeyver" wrote in message ... I'm trying to make a 10x scope probe that is capable of dealing with slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. Thank you. al |
#14
Posted to sci.electronics.design,sci.electronics.repair,aus.electronics
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What can I do to keep this board from warping?
On Fri, 25 Sep 2009 16:02:55 -0700 (PDT), mickgeyver
wrote: I'm trying to make a 10x scope probe that is capable of dealing with slightly higher voltage levels of about +/- 20v yet at a high impedance ~20Meg. This link "http://picasaweb.google.com/ UncleAltheKiddiesPal/Probe?feat=directlink" has some photo's showing the probe and board warpage. The board was made from double sided 0.020-inch stock etched with a PCB milling machine (perhaps part of the problem). It is (obviously) hand assembled. I would appreciate any tips or techniques that I could use to keep this board from turning into a potato chip during assembly. Thank you. al Purchase rigid (of course) Silica plates (heat sink media). You could very likely get 0.020" thickness, no problem. You could also likely get the exact size you need as well. Then you proto by dead bug (or not)glue the chips and other parts on, and hand wire the nodes between them. Your proto could then turn into a flex circuit to replace all the hand wiring for the SMD circuitry, glued (attached) onto one of your already existing Silica base plates that you bought say 100 of for the first proto and production runs. As small as it looked, I could easily build many of them a day even as proto style. But the flex circuit with the heat absorbing capable Silica back plate sounds like a candidate for being called a solution. |
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