Fine Pitch soldering chips and different Flux used

Discussion in 'General Electronics Chat' started by relicmarks, Apr 29, 2008.

  1. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    How do you guys solder Fine Pitch chips to a PCB?

    Because some companys use ROSIN FLUX Liquid and its really hard to remove the fine pitch chip because its sticky from the rosin and it lifts up the pcb pads

    The water-soluble Flux Liquid seems to be better cause its no sticky at all

    I use a Flat angle blade on my soldering iron tip

    How i solder in the Fine pitch chip is i tack in all the 4 pins of each 4 conners on the chip

    If i SLIDE the soldering iron tip from #1 across the other fine pitch pins it creates alot of SHorts because its fine pitch very close pins

    The Rosin Flux makes it worse creates more shorts plus its very sticky

    When i was cleaning the Rosin flux off the fine pitch pins with a brissle brush it bent all the pins to the sides because some of them wasn't solder to the pads so it ruined the chip

    I think using a small paint brush with rubbing achol. was much more GENTLE to use on the fine pitch pins without bending them to the sides

    How do you guys clean with >? and what kind of brush to be gentle on the fine pitch chips?

    What types of flux you guys use?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    I use Kester 44 in .025" with the flux rolled in. That is 63/37 eutectic lead/tin. I have the pads tinned with a commercial plating solution. Then I put a bit of solder on one pad and tack down one of the corner leads. With only one soldered, it's easy to adjust the IC.

    My soldering tip is about .032", so soldering .050 centers isn't too hard. Always heat the pad before the lead. As in many things, lots of practice makes it work.
     
  3. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    some PCBs pads lift up very easy why is that? while other PCB pads stay ?

    It seems that the HEAT gun for fine pitch pads can lift the pads up but how do you prevent this? it is just cheap PCB pads? but what can the companys do to make the pads stick better with them lift up when using heat guns??

    How do you guys take off the fine pitch IC chip?

    Do you guys use a razor blade or flat head screw driver place it under the chip and lift it UP while using the heat gun?

    Sometime i can't find "Tweezers" with the IC chip WIDTHS to grab onto the chips body to lift it up , so i use a razor blade and place it under the IC chip and lift it up
     
  4. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    NO i'm talking about "LIQUID flux"

    The water-soluble Flux Liquid VS Rosin Flux LIQUID FLUX

    On has no rosin thats the water based flux liquid its clear no sticky at all
     
  5. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    My soldering tip is about .032", so soldering .050 centers isn't too hard

    1.) What if the soldering tip is still to big for the Fine pitch PINS ? how would i to solder each fine pitch pin without creating solder shorts?

    2.) Because if i slide the soldering iron across the pins it creates alot of shorts even when i use LIQUID FLUX and i have to use solder wick its just a mess

    I have the pads tinned with a commercial plating solution

    3.) What commercial plating solution do you use? whats the name of it??
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    That is apparently due to differences between board manufacturers and processes. One factor is how the copper is made to stick/plate to the board. Another is the material of the board per se. Look up "glass transition temperature for FR4" and you will find more than you want to know. With increased use of lead-free solder, I suspect we will be seeing more of the higher temp boards in common use. John

    Edit: I happen to use Injectorall (this is not a plug for them), but its site claims a higher glass transition temperature, and I have never had a problem with pads lifting.
    See: http://www.injectorall.com/techsheetFR4.htm
     
  7. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    One factor is how the copper is made to stick/plate to the board.

    1.) is it the Glue that is used?

    Another is the material of the board per se.

    2.) What types of material of boards is there please?
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    With skill and luck, I get away with Ever-Muse boards from Circuit Specialists. Dead cheap, 1/2 oz. copper, but pretty good positive resist. Pads usually don't lift until the third desoldering.

    They have both FR4 and phenolic, which are the two types of PCB stock. If you have really exotic requirements, you can get exotic materials like teflon.

    Don't think you're gonna have much luck on the Cuproposit (tm), as the jug I'm working out of is at least 45 years old. I hear bad things about Tinnit, but have never tried it.

    Only Oompa-Lumpas can hand solder 25 mil centers.

    Relicmarks - one posting at a time, please. It's really hard to keep track of all those machine-gun questions. Don't you have any textual material? Not even from the local library? Some of your questions are so basic, and then some are for testing that is really specialized. It's hard to figure out how to word replies appropriately.
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    A cheap soldering iron gets too hot and the over-temperature melts the glue and lifts the pcb pads.
    A good soldering iron has temprature control so it never gets too hot but still has a lot of power when it is needed.

    A cheap soldering iron gets so hot that the flux burns away instead of doing its wetting and cleaning jobs.
    The tinning on the tip of a cheap soldering iron that is too hot also burns away.
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    It's interesting to see that comment. I used to use Tinnit on everything. Heated to 60°C, plated, then after cooling, kept it in the refrigerator. That way, I got more than a year of use for occasional boards. The last batch I had really messed up the board. It was fairly new, and I got dull, uneven plating. I stopped using it and just use a good bit of rosin flux, which I wash off after I am done. I spray with a light coating of conformal lacquer and think the boards actually look a little better. John
     
  11. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    Is it best to use a "HOOF tip- vertical drap soldering" for Quad Flat package chips?

    They have different kinds of flux

    Paste FLUX? rosin flux? water based flux?

    When is it good to use the paste flux?

    When is it good to use the rosin flux since its sticky ?

    They have a FLUX PEN

    This is to removel QFP chips use this = Hand-Held SMD Vacuum Pick-Up & Placement Tool
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    The keys are:

    Cleanliness - (yes, it's next to Godliness in soldering as well as personal hygene and household). If your components aren't clean, you have no chance of producing a decent solder joint. Oils from your fingers are sufficient to hinder a good solder joint. Use isopropyl alcohol to remove oils and contaminants. You can buy 91% in some drugstores; the remainder is water. Don't use the 70%; it'll take too long to evaporate. Use a cheap "acid brush" - they have synthetic bristles that are held in place by rolled-up tin-plated metal.

    If you are dealing with "new old stock" parts, you can remove the corrosion from the parts' leads by a brief immersion of the leads (about 30 seconds) in "muriatic acid", available very inexpensively in pool supply stores, and then rinsing the acid off for several minutes in several baths of clean water, then waiting for them to dry. ** WARNING **This is a HAZARDOUS PROCEDURE THAT MUST BE DONE IN A VERY WELL-VENTILATED AREA, PREFERABLY OUTDOORS WHILE YOU STAY UPWIND!!!

    Equipment - a thermostatically-controlled tip soldering iron that is clean and tipped will help a great deal in making good solder joints. You can get small cans of "Tip Tinner" that makes tinning the tip of your iron a snap.

    Solder - my personal preference is Sn63/Pb37 small-diameter solder. As the tree-huggers encroach upon the industry, this solder will become much harder to get. If you don't believe me, try to buy a can of Freon-12 at an auto supply store in the U.S. - it's not going to happen. But I digress ... back to the thread. The reason for Sn63/Pb37 (commonly called 63/37) is because this ratio of tin/lead is eutectic - it goes directly from a liquid state to a solid state, with no "plastic" state in between. If your components are spotlessly clean, and you apply proper heat, you are virtually guaranteed a good solder joint.

    Practice - makes better. Perfection takes a LOT of practice.

    If you bent a lot of pins on your IC's during cleaning because you didn't solder them correctly - well, you need more practice.

    Lifted pads - you applied too much heat. Practice.

    Get some cheap surplus ICs, and practice soldering them. LOTS of them.

    If the parts, solder and iron are all spotlessly clean - guess what?
    You don't really need flux.

    However, a scientist at a company I used to work for came up with a super concentrated citric acid that was completely water-soluable, wouldn't harm the environment, wouldn't harm people (indeed, it would give you a good dose of vitamin C if you drank some of it) and was much better than using rosin flux when soldering circuits.

    So, pick your poison. Keep everything spotless, and avoid the need for flux.

    Or use the citric acid type flux, and rinse when done soldering.

    Or don't clean anything, use rosin flux, and spend lots of time with isopropyl alcohol and a brush cleaning all of that stuff out of there.

    But really, stop replying to your threads with lists of stuff. It's annoying.
     
    Sculo likes this.
  13. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    To clean the flux and rosin off the boards i heard its good to wash the boards in water and then use "windex"?


    Kester Flux Pen
    Chip Quik - No clean Paste Flux
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    Relicmarks,
    How many people are using your login?
     
  15. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    just me sorry , Im trying to help you guys out to when i reply in my threads too

    Because i go and research with the information you guys give me
     
  16. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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  17. SgtWookie

    Expert

    Jul 17, 2007
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    Look, this is not really acceptable.

    You're asking questions, then it seems like you're ignoring the answers and posting your search results.

    Why didn't you just do the search in the first place, and not post the question that others would try to help you with?

    This is a community of helpful people. However, you seem to pose questions that you answer yourself, while seemingly ignoring the input of forum members whom are trying to help you.

    Frankly, I don't really know why you're still here.

    What's your point?

    You don't want interaction, you want input.

    I don't get it. Why not simply do searches and leave us out of it?
     
  18. relicmarks

    Thread Starter Active Member

    Oct 13, 2006
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    no you guys help me out alot

    im sorry you think like that
     
  19. mrmeval

    Distinguished Member

    Jun 30, 2006
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    I use hot air to remove the chip. It can remove other parts if it puts out too much force. I'm blanking on the brand just now. The better ones allow both the temp and the air speed to be adjusted and have reducer/spreader tips. These are at hardware stores.

    Most surface mounted chips have enough solder on the to tack them down. I use a kester flux pen though will use liquid rosin if needed.

    Since I can't see the pins well I use a microscope meant for small work. I line of the chip and hold it down then tack down the end pins on one side then make sure it's aligned then tack down the other sides. Then use a hoof shaped tip and run a ball of solder down each side. It takes almost no solder to do this. This is for 100 pin devices.

    The chip makers are going to force my company to start using BGA's I don't think we can even afford a BGA rework station.
     
  20. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    What you can use to remove flux depends on what flux you used. You are going to be doing some testing, I presume, so try the water and windex trick with the flux you choose.

    As for me, I just use Kester SP-44 rosin flux. I don't think water removes it. I use absolute alcohol (100%) with a little acetone added. The acetone isn't necessary, but it makes it smell good, and it increases the solvent strength a little. If there are styrene-like plastics on the board, I leave out the acetone. Denatured alcohol(s) will work as well, except there are various formulas for denatured alcohol. Some of the formulas include substances that may also harm the cheaper plastics. Isopropyl alcohol (IPA) also works, but it is easier for me to get the absolute ethyl alcohol than IPA. John
     
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