0.4mm parts like 36-WLCSP (2.49x2.54):  Pretty much impossible to get built? - Page 1
Forum section: electronics / general

author: JoeN
author_rank: Frequent Contributor
timestamp: March 30, 2016, 07:52:54 am
content: With 6/6mil traces and 13/7mil vias being about the standard for almost all the prototype houses, that part seems impossible to get built on any number of layers. It looks like you can't route the inner pins down to sub layers at all because it requires traces and vias that just can't be fit between the balls. How is it done? Can prototyping on these parts be done at all or do you go straight to "production" quality PCB runs that allow for finer drills and copper features? Or is there some way to bang this out on a 4 layer board at OSHPark that I can't think of?Thanks for any help.

author: tszaboo
author_rank: Super Contributor
timestamp: March 30, 2016, 08:35:36 am
content: If you are using a WLCSP the reason for that is because you are designing a PCB the size of a postage stamp, the thickness as small as possible. To fit it into a a phone or smart wearable whatever. Traditional PCB houses dont prototype these PCBs.If you dont design that, just use a bigger package.

author: janoc
author_rank: Super Contributor
timestamp: March 30, 2016, 08:38:28 am
content: Quote from: JoeN on March 30, 2016, 07:52:54 amThat's a tad optimistic - the cheap ones like Seeed, iTead or DirtyPCB can do only down to 8/8.From the cheap(er) ones only OSHPark, Elecrow and SmartPrototyping can do 6/6 - with varying results. OSHPark recommends not exceeding 8/8, but I have never had issues with 6/6 boards with them. The other two - ymmv.I have been explicitly shopping around because of this recently - have a 3x3mm 0.4mm pitch QFN that needs 6mil traces and it exceeds the design limits in many cheap places.

author: DutchGert
author_rank: Frequent Contributor
timestamp: March 30, 2016, 12:22:43 pm
content: In general, >= 1mm pitch BGA you can get away with 6mil/.15mm trace/space 'every proto house can make it' TH stuff>=0.65mm pitch BGA you can still get away with conventional TH boards but need 4 or 5mil/.1 or .125mm trace/space so not every cheap Chinese proto house can do it.<0.65mm pitch BGA's u need to go for micro via's with 3mil spacing or sometimes even 3 mil tracks if u need to access inner pins or route between the micro vía'sI just finished a board that uses a 0.5mm pitch BGA (for an automotive drive assist camera so they are not only used in cellphones nowadays) and had to go for 100um tracks, 75um clearances and .1mm drill/.3mm pad (stacked) microvia's......(the little grid u see in the top right corner is 125x125um)For a .4mm or BGA I assume u have to use 75um/3mil tracks and 75um/3mil spaceBoards will be made in china but European companies line Wurth can also produce these kind of boards. I am truly impressed each time I see one however, its so tiny......This gives a nice overview of 'typical' HDI board design rules:http://www.we-online.com/web/en/index.php/show/media/04_leiterplatte/2012_2/dg_poster_1/141029_DesignRules_HDI_Poster_A2.pdf

author: nctnico
author_rank: Super Contributor
timestamp: March 30, 2016, 02:52:01 pm
content: Still for small production runs (less than 200 pieces per batch) you better stick with 0.1mm traces and 0.1mm clearance otherwise the boards will be very expensive. I once tried to have a design produced with 60um traces and 40um clearance but that was a total no-go (the customer wanted to try and use parts which where available at that time).

author: JoeN
author_rank: Frequent Contributor
timestamp: March 30, 2016, 05:23:50 pm
content: Quote from: janoc on March 30, 2016, 08:38:28 amI order minimum features from OSHPark all the time and have never had a problem, not even once. The boards are always perfect.

author: JoeN
author_rank: Frequent Contributor
timestamp: March 30, 2016, 05:26:01 pm
content: Quote from: NANDBlog on March 30, 2016, 08:35:36 amOk, someone should tell Lattice about this.