Stepped stencils VS flat cheap stencil thickness & PCBWay ladder stencil? - Page 1
Forum section: electronics / general

author: BrianHG
author_rank: Super Contributor
timestamp: August 10, 2017, 05:40:17 am
content: I'm about to order a PCB and stencil from PCBWay. I was going over with a friend who has some SMD assembly experience. I told him I had a PCB with mostly 0805 and 1.27mm pitch ICs, + 5 ICs with 0.5mm pitch. I said I was about to order a 0.12mm thick electropolished stencil from PCBWay. He told me that that thickness might be fine for the 0.5mm pitch components, but for the larger SMD parts, the thickness should be closer to 0.2mm thick. He then went on to say that the industry used step-up and step-down stencils to coat different levels of paste for different pitch sized components & provided me with a web link covering the subject.So far, everything is ok.Now, after speaking online with PCBWay, they told me that a stencil with different heights for different component pitches was called a ladder stencil & the price would be around 3x.Now, when I googled for 'stepped smd stencil', I got PCB industry documents and photos of stepped stencils.When I googled 'ladder smd stencil', I got nothing of the sort.I went back online to PCBWay and asked for a photo one of their 'ladder SMD stencils' and the online agent this time went offline. No photo...Is PCBWay trying to scam me 3x cost on a stencil which a phony name not even google could find a single photo of which will just end up being one of their flat stencils?If I were to go with a cheap 0.12mm thick stencil, how bad will the soldering on the larger components be? I'm only building 10 PCBs and I know that too much paste on my five 0.5mm pitch QFN packaged ICs will just short them out.

author: anishkgt
author_rank: Frequent Contributor
timestamp: August 10, 2017, 05:50:41 am
content: I suggest you try other houses as well like allpcb.com I had my through hole done with them and it was good.Sent from my iPhone using Tapatalk

author: ataradov
author_rank: Super Contributor
timestamp: August 10, 2017, 05:56:37 am
content: Allpcb is the same outfit as pcbway.They are really bad at communication. Your choice is to either risk it once, or persist with questions. They will eventually tell you everything you know.I feel like sometimes they quote ridiculously high price to basically get rid of you, if you ask too many questions.

author: digsys
author_rank: Unknown
timestamp: August 10, 2017, 06:00:44 am
content: A search using .... " surface mount solder stencil stepped " ... found this -geminitec.blogspot.com.au/2014/11/solder-paste-typography-for-pcbs-with.html

author: BrianHG
author_rank: Super Contributor
timestamp: August 10, 2017, 06:31:26 am
content: I believe I will go with the cheap 0.12mm stencil & carefully, visually screen for too lean solder joints on the 1.27mm pitch SO14/SO16 ICs on my design and the even larger 2.54mm pitch SMD connectors which can easily be touched up with a soldering iron.Example photo below of a stepped stencil:

author: elecman14
author_rank: Unknown
timestamp: August 10, 2017, 03:47:41 pm
content: Unless you have really strange pad geometry you can do things like decrease the aperture size to put less solder on a pad. Using stepped stencils seems like a last resort to tuning process problems. If you are doing a small volume it probably is not worth it as others have noted.

author: wraper
author_rank: Unknown
timestamp: August 10, 2017, 04:15:32 pm
content: 0.12mm stencil is completely fine for 0805 and 1.27mm pin pitch ICs. Requiring 0.2mm for that is nonsense. If you need more solder you also can make slightly larger hole in the stencil than actual pad. EDIT, actually if 0.2mm stencil will be used with 100% aperture for 0805 pads, there will be excessive amount of solder which can cause excessive stress and cracks in ceramic capacitors. There is no reason to go beyond 0.15mm for such parts.

author: jmelson
author_rank: Super Contributor
timestamp: August 10, 2017, 07:32:39 pm
content: I make my own stencils from 0.003" brass shim stock. I spent some time tinkering with different stencil thicknesses to find this worked best for me. Then, I had to find the right factor to shrink the apertures by. For 0805, you can shrink slightly or just leave them full size. As the chip lead pitch decreases, you have to shrink the apertures more and more to avoid solder bridges.Jon

author: BrianHG
author_rank: Super Contributor
timestamp: August 10, 2017, 10:26:20 pm
content: Well, I made the order and in 2-3 weeks, I'll report the results.I went with 0.12mm for fine pitch of 0805 parts and smaller, 2mm pitch for the large 2.54mm pitch SMD connectors and SMD relays.Wish me luck.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 10, 2017, 10:37:42 pm
content: For 0.5mm pitch you don't need any fancy stencils - a normal flat one is fine.