Tssop-8 hand mounting advice?

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mangocats
 
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Tssop-8 hand mounting advice?

Post by mangocats »

From what I understand, surface tension and faith are the primary ingredients involved in mounting small surface mount parts like a Tssop-8.

I'm presently trying to mount some LM8272s on the Adafruit 1212 breakout boards (no, as far as I know the 8272 doesn't come in any larger packages) and I would appreciate any tips or pointers.

I already have the finest point tip installed on my soldering iron, temp set at 650F seems to be flowing the solder on the pads well enough, but I can't get the chip pads to stick...

Update: through the application of a lot of faith, I more or less flooded the pins with melted solder, bridged everything, then sucked off the excess. One side looks hopeful, the other not so much. Image

Tips still appreciated, also: how concerned should l be about cooking the chip internals?
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sj_remington
 
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Re: Tssop-8 hand mounting advice?

Post by sj_remington »

That does not look good. The board should not be powered up, as pins may be short circuited. I would remove the excess solder using solder wick: https://youtu.be/M5wRYLXS_wY

I suggest to look for junked circuit boards to use as testbeds for improving your soldering skills, rather than using new parts.

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Franklin97355
 
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Re: Tssop-8 hand mounting advice?

Post by Franklin97355 »

You need to have some flux to allow the solder to flow well. There are this from us:
https://www.adafruit.com/product/3468
https://www.adafruit.com/product/2667
or you might pick up that from your local merchant but make sure it is for electronics.
What solder are you using?

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adafruit_support_bill
 
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Re: Tssop-8 hand mounting advice?

Post by adafruit_support_bill »

The biggest part of the problem is that the chip is not aligned properly. The chip pins on one side line up nicely with the pads. But on the other side of the chip, the pins are positioned between the pads - so the solder bridges to the pads on both sides of the pin.

Make sure that the chip is aligned with all of the pads before beginning to solder. Sometimes it helps to tack-solder a pin in one corner to hold it in place before proceeding to solder the rest of the pins.

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mangocats
 
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Re: Tssop-8 hand mounting advice?

Post by mangocats »

Franklin97355 wrote: Sun Sep 18, 2022 6:01 pm You need to have some flux...
What solder are you using?
So far I have been relying on the flux core of the solder, but am ready to try a flux pen to see if that helps.

The brand on the solder is Towot, label says 60/40 Sn/Pb 2% rosin core 1.2mm... yeah a little on the big side, but mostly I have been transferring the solder to the work via the pointy iron tip.

My main challenge was getting the first pin tacked down, never really did until I flooded two or three pins with solder, it was like the pin wasn't heating enough to take the solder - maybe more flux will help.

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Franklin97355
 
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Re: Tssop-8 hand mounting advice?

Post by Franklin97355 »

You should be applying the solder directly to the pad so the flux has a chance to do its job. Take a look at Colin's tutorial https://www.youtube.com/watch?v=QKbJxytERvg

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sj_remington
 
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Re: Tssop-8 hand mounting advice?

Post by sj_remington »

but am ready to try a flux pen to see if that helps.
Paint the pads with solder paste, drop the chip down and make sure it is properly positioned (it will stick to the paste), then give it a gentle blast with an inexpensive hot air rework gun like the 858D: https://www.ebay.com/itm/403207390848

The entire operation takes 1-2 minutes and usually gives perfect results. If it doesn't, give it another gentle blast (you will see the solder liquify), pick the chip up with tweezers and start over.

Tip: Buy solder paste in small containers, close the container tightly immediately after use and freeze it for later. The stuff I use dries out very quickly and becomes useless.
Last edited by sj_remington on Sun Sep 18, 2022 9:30 pm, edited 1 time in total.

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Franklin97355
 
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Re: Tssop-8 hand mounting advice?

Post by Franklin97355 »

sj have you tried putting a little flux in the hard solder and mixing it? I was able to revive some of mine at least a bit ( and not well)

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sj_remington
 
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Re: Tssop-8 hand mounting advice?

Post by sj_remington »

I have seen articles on how to revive dried solder paste, but have not tried any of the suggested remedies.

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mangocats
 
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Re: Tssop-8 hand mounting advice?

Post by mangocats »

Attempt #2 went a little better, I feel like the flux pen helped quite a bit with getting the chip pins to take solder, and the alignment was good, but I still ended up with a blob-bridge that I could not remove:
IMG_20221009_163415296.jpg
IMG_20221009_163415296.jpg (37.45 KiB) Viewed 1888 times
Attempt #3 failed when the 2nd pin attach went crooked and straightening... didn't:
IMG_20221009_164248965.jpg
IMG_20221009_164248965.jpg (20.59 KiB) Viewed 1888 times
Next came a redesign for a bit more power, and larger SOIC-8 packages, three wins on the first try:
IMG_20221009_172506295_HDR.jpg
IMG_20221009_172506295_HDR.jpg (101.98 KiB) Viewed 1888 times
Amazing what difference a little extra size makes.

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