Connect with us

LTC4425 chip is insanely small!!!

Discussion in 'General Electronics Discussion' started by pityocamptes, Sep 27, 2012.

  1. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    I've done reflow, but this chip is SMALL!!! Ok, anyone have suggestions on reflowing a chip the size of a the letter "E" on the esc button on a keyboard??? Same process, something different? I usually use a heat gun... I'm going to have to get a magnifying glass or something!!!
     
  2. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    MSOP or DD package? The exposed legs of the MSOP will aid in manual reflowing...

    Either way it's a small chip, taking off it easy resetting is a little trouble, just need to clean the pads of all existing solder (use wick) and apply a small amount of fresh good solder paste, use a needle or razor to get a clean application, set and reflow... If I was doing several of them I would get a stencil to better apply the paste...

    You might also have better luck with a toaster oven vs a heat gun so you don't blow the chip around... It also might not hurt to be liberal on additional flux at the end of the reflow, followed by another quick reflow or clean up with an iron...
     
  3. BobK

    BobK

    7,599
    1,641
    Jan 5, 2010
    Well, I solder chips that small with a soldering iron. Is it a sot-23? And yes, a magnifying glass is essential (at least for me.) I wear one attached to a headband.

    bob
     
  4. BobK

    BobK

    7,599
    1,641
    Jan 5, 2010
    Oh, now I remember, I warned you that it would not be easy! The pad makes reflow necessary.

    Bob
     
  5. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012

    MSOP package. Thanks. I have a thicker diameter solder, ran out of the very fine solder. I wonder if they have different melt rates? Do you think that the thicker core solder will be fine? How long would I leave it in a toaster oven? Will I damage the chip - that is what I am concerned about. Thanks!
     
  6. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Hahahaha, yea I know. It was the only chip I could find that will hopefully work with my project...
     
  7. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    Unless you do your own board and extend that pad outside the edge of the chip so you can sorta heat it with an iron, either way reflow is by far the best option...
     
  8. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    I bought a MSOP proto board online. So it has the center ground pad, and pin pads.
     
  9. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    If they are the same composition melt rates will be consistent... Solder paste is really your best choice here, not solder...

    I would use paste, way too hard to get the chip to lay flat on the thermal pad with regular solder, not impossible but it certainly complicates the issue...

    BTW, in addition to what I said about extending that thermal pad outside the chip, you can also put a larger plated via (hole) dead center under the chip that way you can solder from the other side of the board and let the solder flow through the via...

    Don't use an oven you cook in, they are only $20 new so get a new one... There are better ways to mod the oven and better ways to follow the reflow temp profile but that is another subject entirely... Here is the quick and dirty that will work for 'leaded' solder, lead free might take more time...

    Turn the oven on an pre-heat to about 275-300º F
    Once pre-heated place the board in the oven, (center it if possible not directly over an element)
    Let the board pre-heat for 3-5 mintues
    Crank oven to full power aka 'broil' on most toaster ovens...
    Set timer for 3 minutes! Watch the board with a flashlight during this 3 minutes... Reflow should happen at about 2½ minute mark, watch for this, it's clear if you are using solder paste... You want to cook for about 20-39 seconds after the reflow happens...
    At the 3 minute mark, dial the heat back to 275-300º and open the door for a bit to help drop the temp, let sit of 3 more minutes...
    Turn off oven open door and let cool slowly to room temp...
    Remove board...

    As for damaging the chip they are designed to be reflowed... The only thing you have to pay attention to is some chips will absorb moister and they will need longer and slower preheat cycles if they get contaminated... If the chip is one of these kinds it will come in a ziplock with a moisture sensor or be noted in the datasheet...
     
  10. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Thanks. I don't have any solder paste. Hmmm... anyone know of a brick and morter store that carries it? I have a radio shack, lowes, home depot close by. There is an electronics parts store open this Sat. but its way on the other side of town. May have to go there though if the other stores don't carry it... thanks.
     
  11. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    I get it online, it has a short shelf life and 'technically' it should be refrigerated... Most legit US sellers will charge you overnight shipping and dry ice packing... I doubt you will find many local shops that carry it... I get and keep on hand a few of the cheap Chinese pill box sized containers, and I have never had any issues with it being 'stale' even though it's not refrigerated, takes weeks to arrive and sits in my desk for months... I also have a big 1lb tube of it I picked up on Ebay cheap that was 2 years expired (now it's nearly 5 years expired) I need to cut it with a little rubbing alcohol and/or no clean flux to get it 'creamy' but it still works plenty well...

    May I suggest you order some solder paste and wait it out, if you want to play around right now may I suggest you get some wrapping wire and simply solder the wire to the legs and play while you wait... Don't forget to wick the solder off the chip when you do go to set it...
     
    Last edited: Sep 27, 2012
  12. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    I have two sample chips, so I have some room to play with. If I decide to reflow the part with regular solder, what tips can you give me for this very small part? Plus this MSOP has the ground on the center pad, I have not reflowed small chips like this before. Do you basically "tin" a small amount of solder onto the center pad, small amount on the leg pads and the heat? Thats at least how I have done it before with components that only had the legs. Not sure the best way to do a component with a center ground. Thanks!
     
  13. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    Yeah you have the basics, tin all the pads, flux the part and set it on top of the tinned pads... Since you will be balancing on tinned pads vs sticking it in paste you might find it beneficial to use something to help hold the chip centered over the pads... You can get some small square nuts at the hardware store, using two of them (on the ends) you can sorta lock the chip into position... This is if you are using an oven... If you are using a heat gun, get the board nice and toasty (I do this on a one foot square marble floor tile, the tile not only protects the work surface but it helps hold the heat longer, have the chip fluxed and ready to grab with tweezers... Get the tinned pads nice and warm and drop the chip hoping you get it centered and that the tension of the solder helps it jump into position...
     
  14. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012


    Thanks. I may try this on a heat plate that I have...
     
  15. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Reflowed the chip yesterday. I thought it came out fine. PIA though, very small! Anyways, is there a way to test the chip on the board to make sure all the connections are good, and that the heat did not damage the chip? I used a heat gun on low and held it about one inch off the chip until the solder melted, slightly push down on chip with dental tool, and then removed heat, and let naturally cool. Thanks!
     
  16. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    As I said the chip are tolerant of the reflow heat, look at it under a magnifier glass and make sure the solders are clean and look for a hairline crack in the chip... In all my years I have only 'wrecked' a few chips by reflowing, and almost all of them were obvious with a crack, likely due to uneven heating... Out of 1000s upon 1000s of chips the 'wrecked' ones are single digits at best, failure from reflow is uncommon unless you really toast the heck out of it...
     
  17. pityocamptes

    pityocamptes

    79
    0
    Jul 26, 2012
    Thanks. All legs look good. No cracks or anything else...
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Similar Threads
Loading...
Electronics Point Logo
Continue to site
Quote of the day

-