Starting with SMT process (stencil, manual place, reflow bake)...what do you do. - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: April 14, 2015, 08:46:32 pm
content: Hi,Starting with SMT process (stencil, manual place, reflow bake)...what do you do with part sizes.Do you stick with a particular size 0603, 0805, 1206 for caps/res?Do you use resistor arrays when you get 4 or 8 of the same type or just use individual resistors?Do you try to do a small part count by combining everywhere you can (using a prebiased transistor instead of a regular one and a base drive resistor), or stick to simplier parts instead of combined ones.Thanks,Alan

author: tggzzz
author_rank: Super Contributor
timestamp: April 14, 2015, 08:52:29 pm
content: Quote from: alank2 on April 14, 2015, 08:46:32 pmMy experiences are athttps://entertaininghacks.wordpress.com/2015/03/25/creating-pcbs-with-surface-mount-components/and are mostly positive.QuoteUse whatever is convenient. A principal reason for using resistor arrary is to get better matching.QuoteDepends on the economics.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 14, 2015, 09:06:14 pm
content: The cost of placing a resistor is way more than the cost of the resistor, so yes, use resistor packs.Minimising number of different parts is good, but don't forget the above if using multiple resistors to replace a single one just to avoid a new value.Digital transistors, yes. Dual ones even better. but again, balance this with not using umpteen different ones.Don't use parts smaller than needed, but there's no need to go over 0805 unless you need the power rating or length.You don't want to go below 0603 unless you really need to reduce size.

author: Falcon69
author_rank: Super Contributor
timestamp: April 15, 2015, 01:58:47 am
content: why would resistor packs be less charge for placing?So far, all the PCB assembly places I have checked chargesPERPad. example, .03 per pad. A resistor has 2 pads, so 6 cents to place it. A resistor pack with 4 resistors has 8 pads, so that is 24 cents to place.

author: alank2
author_rank: Super Contributor
timestamp: April 15, 2015, 02:00:46 am
content: I'll be placing all parts by hand in my garage!

author: Falcon69
author_rank: Super Contributor
timestamp: April 15, 2015, 02:12:11 am
content: in that case, if you have a LOT to place, invest in a vacuum pick up tool, or make your own. It's easy to make your own. Plenty of info around. If you are itnterested, you can PM me, and I'll explain how to make one using a Tetra Aquarium Pump.

author: alank2
author_rank: Super Contributor
timestamp: April 15, 2015, 02:18:14 am
content: Thanks Falcon69, I appreciate the help! I have a solder paste dispenser and it actually works pretty good as a vacuum pen.

author: Falcon69
author_rank: Super Contributor
timestamp: April 15, 2015, 02:22:06 am
content: Oh, good, you are on a good start then. Do You have a reflow oven? If not, one can be made pretty easily using a toaster oven and a controller.Also, if you order a lot of boards, pay the extra 20 bucks for a stencil. It's worth it. So much quicker than a paste dispenser pen.

author: alank2
author_rank: Super Contributor
timestamp: April 15, 2015, 02:26:00 am
content: Quote from: Falcon69 on April 15, 2015, 02:22:06 amYes. I made an AVR based PID controller for it.Quote from: Falcon69 on April 15, 2015, 02:22:06 amI learned this almost immediately. Can't say I'm very good at stenciling, but so far so good.

author: Falcon69
author_rank: Super Contributor
timestamp: April 15, 2015, 02:28:38 am
content: I've had to update some of my component pads to a bigger size because I just could not get the paste to flow into the stencil correctly. Sometimes small, is just too small.

author: alank2
author_rank: Super Contributor
timestamp: April 15, 2015, 02:43:50 am
content: Quote from: Falcon69 on April 15, 2015, 02:28:38 amIt is quite funny that you mention this, that is the only big problem I've had. Pad size too small, not enough paste, didn't wick up into the component!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 15, 2015, 07:57:34 am
content: Quote from: Falcon69 on April 15, 2015, 01:58:47 amBecause you are placing 4 resistors in one go, so 25% the cost of placing 4 seperate resistors

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 15, 2015, 08:01:11 am
content: Quote from: Falcon69 on April 15, 2015, 01:58:47 amI've never come across that - all chip type parts take exactly the same machine time, it's only stuff like larger ICs that need extra vision time and nozzle changes that take longer

author: zapta
author_rank: Super Contributor
timestamp: April 16, 2015, 02:52:11 pm
content: Quote from: alank2 on April 15, 2015, 02:18:14 amWhat model? Does it require external air pressure supply?

author: alank2
author_rank: Super Contributor
timestamp: April 16, 2015, 02:57:43 pm
content: Quote from: zapta on April 16, 2015, 02:52:11 pm982 type, it looks just like this:http://www.ebay.com/itm/SOLDER-PASTE-GLUE-DROPPER-LIQUID-AUTO-DISPENSER-CONTROLLER-FIRST-CLASS-ba-/171203317346?pt=LH_DefaultDomain_0&hash=item27dc834e62Quote from: zapta on April 16, 2015, 02:52:11 pmYes.To use it as a pickup tool I just removed the white plastic pusher from the syringe and turn up the vacuum until it is just right...Not sure if something else is more suited to being a pickup tool, but I already had one of these.

author: zapta
author_rank: Super Contributor
timestamp: April 16, 2015, 03:14:19 pm
content: That's a nice machine. I wouldn't mind to have one but I don't want to deal with air compressors.

author: alank2
author_rank: Super Contributor
timestamp: April 16, 2015, 03:18:25 pm
content: zapta there was another thread going about pickup tools that showed one at amazon made for picking up gem stones that didn't need a compressor.

author: zapta
author_rank: Super Contributor
timestamp: April 16, 2015, 04:24:02 pm
content: Quote from: alank2 on April 16, 2015, 03:18:25 pmI do have that gem picker. I was asking here about the dispensing side. I am using stencils but would be nice to have a good dispenser. My 'lab' is at my home office and I don't want to deal with a separate large compressor or air tank.

author: alank2
author_rank: Super Contributor
timestamp: April 16, 2015, 04:25:59 pm
content: Quote from: zapta on April 16, 2015, 04:24:02 pmFor me the dispensing was disappointing. I probably wasn't using the right tip or right paste. It did a perfect job of dispensing liquid and it will dispense paste, but it tends to stick to the dispenser needle. If I had a large prototype board to do and no stencil I'd use it though...

author: zapta
author_rank: Super Contributor
timestamp: April 16, 2015, 04:53:54 pm
content: Iantube has a video on YouTube demonstrating a cheap dispenser he got at China. It seems to work well for him.