Leadless packages on milled PCBs with no solder mask - Page 1
Forum section: electronics / general

author: Ammar
author_rank: Regular Contributor
timestamp: October 06, 2016, 11:13:14 pm
content: Hello,I have a PIC10LF322 in a DFN8 package and a DRV8838 from TI in a WSON package, both with 8 pins. I milled a PCB and I am trying to solder these devices to the board. I have tried feeding solder to it, hoping it would go under the package, this didn't work. I have also tried cutting a stencil out of 50 micrometer thick metal. I could place solder paste onto the pads, but when I heated it with a hot air gun, the solder didn't grab the leads.A friend suggested it is hard to do this by hand without solder mask. Has anyone had any success? I found numerous videos and resources, but they tended to use PCBs with solder mask. Should I try a thicker stencil and have another go with the milled PCB? or cut my losses and send the PCB out to be made? If I missed a previous thread on this, let me know.

author: Jeff_Birt
author_rank: Regular Contributor
timestamp: October 06, 2016, 11:17:45 pm
content: Extend the pads out from the package almost as if it had leads. This gives you a place to apply your iron and solder. Tin the pads, just a flat thin layer, use plenty of flux and use the extended pad to apply the solder.

author: Ammar
author_rank: Regular Contributor
timestamp: October 07, 2016, 12:18:38 am
content: Ah, great idea to tin the pads first. I will have to get my hands on some flux too. Thanks for that.

author: janekm
author_rank: Unknown
timestamp: October 07, 2016, 02:50:49 am
content: Also just to check that you sanded the surface of the PCB after milling, the burrs could really mess up things otherwise.

author: nanofrog
author_rank: Super Contributor
timestamp: October 07, 2016, 04:49:44 pm
content: Another method you might try:1. Clean the pads to be sure any burrs and other crap are removed.2. Pre-tin the pads with your iron.3. Add fresh flux.4. Place part.5. Use hot air.

author: Jeff_Birt
author_rank: Regular Contributor
timestamp: October 07, 2016, 05:59:34 pm
content: Quote from: janekm on October 07, 2016, 02:50:49 amVery good tip! Use something like 400 grit paper or a scothch brite pad.Quote from: Ammar on October 07, 2016, 12:18:38 amFlux is a must for soldering. I am amazed at the number of folks who have been soldering things for years without the aid of flux. Your solder may have a flux core but it is not good enough in many cases. For general purpose use rosin paste flux is good to have on hand and a small tin will last you years. For surface mount work I like to use a liquid flux in the form of a flux pen. When you have the occasion where you have a difficult spot to solder and cleaning with scotch brite is not possible (or was not enough alone) apply flux to the joint and heat up the flux alone. As the flux burns off it will clean the joint, let it cool apply more flux and then solder.

author: nanofrog
author_rank: Super Contributor
timestamp: October 07, 2016, 11:39:30 pm
content: Quote from: Jeff_Birt on October 07, 2016, 05:59:34 pmFWIW, MG Chemicals sells their liquid RA in small bottles suitable for hobbyists (100ml & 1L). Then use whatever method you wish to apply it, such as a refillable pen, brush pen, brush bottle, needle bottle, ... Great for PTH and tinning wire as well.Much cheaper than buying the disposable pens.

author: janekm
author_rank: Unknown
timestamp: October 08, 2016, 10:49:10 am
content: Quote from: Jeff_Birt on October 07, 2016, 05:59:34 pmO.P.I nail buffers (the ones with 4 sides in particular) are amazing for this and many other polishing needs. I discovered them from a Shenzhen polishing supplies shop.They are 3000/7000 grit equivalent but very quick, they turn a CNC'd PCB smooth and shiny in seconds without removing too much material.