suggestions to lower per unit cost and/or labor on my design - Page 1
Forum section: electronics / general

author: bragma
author_rank: Newbie
timestamp: December 28, 2021, 03:25:58 pm
content: I have a small cost-sensitive hobby-type project that I build and sell. Maybe 500-1000 pieces per year. I am looking for ways to reduce my per unit cost and also cut down on the assembly labor.Image attached.Things I've done so far:Changed to JLCPCB for lower cost.Converted to SMT so I can source lower cost parts and have them assembled by JLCPCB. JLCPCB populates 3 components and then I add the 8 pin microcontroller and a 2 pin through-hole device by hand.Added edge contacts so I can plug into a mating connector on a custom programmer PCB & flash the microcontroller. (Instead of clipping onto the microcontroller leads with mini-grabber clips.) Programming takes place before adding the 2 pin though-hole device as it mostly covers the edge contacts after installation.I have manually panelized the design myself (no v-scores, no mouse bites) and cut them apart with an abrasive blade on a chop saw. A panel currently consists of (3) boards as that is the size limitation of my very old paid-for v4.16 Eagle CADsoft. Panel size is approximately 60 x 85mm at the widest dimensions.JLCPCB will only build 50 panels for me at a time as this seems to be a limitation of their assembly service.My thoughts:To reduce per unit cost: Change to a different CAD program (Kicad?) that will allow for larger size and more boards in a panel?To reduce labor: Could I add routing and mouse bites to manually snap the boards apart? I am concerned with running afoul of JLCPCB's "different design" criteria and also retaining enough rigidity for their assembly service. Also, I don't want to introduce too much stress around the capacitor, microcontroller, or DIP switch when snapping the boards apart. There isn't much margin around the components to the edge of the PCB. Need some real-world experience in this area.Suggestions?

author: gnuarm
author_rank: Super Contributor
timestamp: December 28, 2021, 04:13:06 pm
content: Yes, a different CAD program is in order. If you have a net list in PADS format, there are plenty of layout programs you can use. This board is simple enough you could do it all by hand without a net list. This would let you make any size panel you want. I use FreePCB which works great and is easy to learn!http://freepcb.com/KiCad is also an option, but may take more time to get up to speed.The mouse bite thing is fine, but you will still need to hand dress the mouse bites with a file unless it's ok to leave them. V-scoring requires a similar machine to break apart the boards and that can only be done on straight lines across the entire array. Otherwise you will spend lots of time with an Xacto knife before the boards will separate. (BTW, they call this an array. The panel is the large PCB sheet the fab house starts with.)Do you not let JLC solder the MCU because it's not one they carry? Can you switch to an MCU they do carry? They've got plenty to choose from. I don't think they assembly through hole devices, so you are stuck with that one... or two.Yes, your parts are very close to the edge of the boards. The cap is through hole, so it won't "feel" the bending so much, same with leaded parts, but anything surface mount with no leads will. I think I see one cap next to the MCU. Turn it 90 degrees and you should be ok. You won't be "bending" the boards that way, but this is still good practice to protect the cap.I see other through holes near the cap and one board is different with extra holes. Can you explain?BTW, doesn't JLC offer to "panelize" the boards for you? I know they do some groady stuff with pricing, but I thought they were good with this? What per board price are you looking for? Are there other houses that can do this as cheaply?

author: jmelson
author_rank: Super Contributor
timestamp: December 28, 2021, 05:10:10 pm
content: Well, I have gone through several passes of cost reduction on some of my products. I found by looking through distributor web sites that there is a LARGE variation in cost of VERY similar components. I now buy most of my 2-part header/screw terminals from a local manufacturer's stocking rep at half the cost from Digi-Key. That helps a LOT! I have found some DIP switches that are way cheaper than other brands, and so on. Just keep looking for better prices.At least, PCBway will panelize single-instance PCBs for you, with mouse bites or V-score as you desire. I assume other board fabricators can do the same.Jon

author: bragma
author_rank: Newbie
timestamp: December 28, 2021, 05:28:15 pm
content: JLCPCB does not carry the microcontroller that I use. Last time I checked, they had no other 8 pin microcontrollers in stock that I could use.JLCPCB will not send v-scored boards through their assembly process. They specifically say to panelize them with stamp holes.The one through-hole item that I install comes in a variety of footprints which is why you see all the extra holes on the right side of the board. Basically I hedged. In the event I run into availability issues with my preferred component, I can switch to another manufacturer/footprint for the item.Same thing with the through-holes under the SMT battery holder. If JLCPCB can't supply the SMT battery holder, then I can use a through-hole version like I did in the past.The one board is slightly larger with an extra set of hole as an experiment I performed on the last batch I ordered. I found a physically larger through-hole device that I wanted to evaluate. This larger option can go away in the future and back to the smaller size such that every board in the array is identical.Turning the SMT capacitor 90 degrees is good advice if I proceed with mouse bites. Thanks.

author: bragma
author_rank: Newbie
timestamp: December 28, 2021, 05:47:38 pm
content: jmelson, I found that JLPCB's cost on components was the same as or significantly less than I could get from any of my local distributors. So I'm basically getting their assembly service for the free after I pay for the cost of components they supply. I do try to shop around on the remaining items that I supply to get the best price.JLPCB won't panelize PCBs with their assembly process. They state, "The PCB specs you chose are not available for SMT assembly. To have your PCB assembled, please reset the PCB specs. Panel By JLCPCB" option is not supported" So, unfortunately, I have to panelize them myself. To this end, I'm hoping somebody may have some practical suggestions for appropriate mouse bite spacing to make the boards easy to snap apart while still maintaining enough rigidity through JLCPCB's assembly process. (How many sets of mouse bites across an 80mm distance are appropriate?)The only way I can think of to reduce component/board cost is to buy larger quantities or find a different supplier. For my relatively low volumes, I don't know of any vendors that are more cost-effective than JLCPCB. So this means larger arrays as JLCPCBs assembly service is a max of 50 pieces.

author: gnuarm
author_rank: Super Contributor
timestamp: December 28, 2021, 06:30:22 pm
content: Quote from: bragma on December 28, 2021, 05:28:15 pmSo why can't you use a 10, 12 pin or 14 pin device? JLC has some wicked good pricing on parts like MCUs if you don't mind using Chinese clones of name brand parts. I can't imagine they can't get you a larger part at a lower price. Looks to me like you could use a 16 pin device if you had to. I guess the question is for 1000 pieces a year, how much effort are you willing to spend?

author: mariush
author_rank: Super Contributor
timestamp: December 28, 2021, 06:36:58 pm
content: Why is the first board wider than the others?Nah, I'd get rid of that lip on the side, if the only reason is there is for programming the micro.Here's a suggestion : have a couple of pads (or as many as needed) on the bottom of the pcb under the micro or around the battery area, and make some frame from wood or something and place spring like contacts on the frame where the pads on your boards would be ... you could even use some shitty battery contacts like these for example :https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/62879-1/1151360Basically, place the cut board in your wood/plastic/metal frame, press it down with a finger for good contact, press a button to flash your micro .. 5-10s job.So without that lip you can make your board a rectangle, which would maybe allow to have some vscoring if it's free (even if it's just one dimension), or you cut them yourself... and maybe you could fit more boards on the panel.Looking at the pictures, you should have room to add footprint for a 10-12 pin microcontroller -- basically have one row of contacts in the center of the 8pin micro's footprint...

author: gnuarm
author_rank: Super Contributor
timestamp: December 28, 2021, 06:38:28 pm
content: I assume your board is about 40 x 80 mm? I would use a set of five drill holes (smallest JLC will do) spaced 2x the diameter apart leaving 1x hole and 1x board. Space these 1 inch apart or so. I did an array with longer boards and didn't use enough. The thing was very hard to assemble with lots of sagging.Do you have tools to spit out the placement file for the entire array? It gets messy with the component numbering if you do an exact copy with the same numbers on each board silkscreen. I don't know if that is important to you, I don't see any ref des on the silk in your photo. I think FreePCB will generate an array as a menu option.

author: bragma
author_rank: Newbie
timestamp: December 28, 2021, 09:43:16 pm
content: I just looked at JLCPCB's microcontroller stock again. As best I can find, they have no meaningful stock in any low pin count devices at the moment. Closest option would be a 20 pin device but I'd have to buy 2500 pieces at a 20% premium over what I already have on hand.Maybe when this semiconductor shortage goes away it will be easier to change microcontrollers. I've sort of looked at some of the Padauk controllers in the past but none are available right now.As far as the edge connectors, they have 2 functions. While they are used for programming, they also physically support the through-hole device after it is installed. To help illustrate this, attached is a new image that better represents the footprints of the parts that I've been installing.After the through hole devices is installed, I can reprogram using the 3 holes around the battery if necessary. It is an AVR with UPDI so I bring the +, -, and reset lines out to the area that is covered by the battery when it is installed.

author: bragma
author_rank: Newbie
timestamp: December 28, 2021, 10:00:26 pm
content: Quote from: gnuarm on December 28, 2021, 06:38:28 pmAfter cutting everything apart, a single board is about 25 x 60mm. In the 60mm direction, I am only cutting about 50 mm with the chop saw as the edge connector is about 10mm. Can you clarify what you mean by "leaving 1x hole and 1x board"?No I don't have any other tools except my old v4.16 of Eagle. As far as ref des, the numbering does get messy so I stack all the ref des on top of each other under one of the through hole components where the end user never sees them.If I was to use FreePCB so I could make a larger array, is it also able generate a component placement file with the centers of each component for the pick and place?

author: gnuarm
author_rank: Super Contributor
timestamp: December 29, 2021, 12:08:09 am
content: I'm just talking about the mouse bites. The boards I typically make use 10 mil drills. So the mouse bite is just five 10 mil holes drilled 20 mil centers giving 10 mil of board material separated by 10 mils of hole. The router has to be managed to come within 10 mil of the edge holes. So you need to know the size router bit they use or know exactly how to spec the outline to prevent it from cutting too far or too little. If they cut too little you can always use the saw to cut a bit. You are going to have to touch it with a file to clean it up anyway (or maybe not?), so a bit of saw work is ok I guess.____ ________) o o o o o (____ <--- router cutI would use three of these along each long side and one on each short side. Add a rail around the perimeter to provide better support, maybe a half inch or so wide. It will use a bit of material, but that won't cost much I think. You can add some fake circuitry to the rails to help keep it from looking so much like an array maybe? Actually many places use this rail to add test circuitry to verify the performance of the PWB. I expect you won't need that.

author: gnuarm
author_rank: Super Contributor
timestamp: December 29, 2021, 12:15:27 am
content: Yes, FreePCB is pretty capable. I don't recall the details of how to generate that file. In the original FPCB a batch mode program was used for that and the configuration file was a bit complicated. FPCB is under new management and I bet the new guy has a better solution, but I don't recall. There's a mailing list.https://groups.io/g/freepcbIt's been a while since I used it and I haven't kept up with the new guy's updates, but I know he's tweaked a lot. It's a friendly crowd, so sign up and introduce yourself.

author: 48X24X48X
author_rank: Frequent Contributor
timestamp: December 29, 2021, 01:57:13 am
content: Here's how I would panel your board. So, maximum you get 500 pieces in 1 order.Don't worry about the pick and place machine side panel requirements, your panel will be part of a bigger panel. So, they will take care of that.I use a 2 mm routing gap as that is the minimum JLCPCB required. For the mouse bite, you can use a 0.7 mm non-plated holes.Other than breaking the mouse bite (which is easily done), you might need to slightly sand off the unevenness after worth if look is your priority. Some people just leave it as it is. I personally will sand it off.And this board can be easily moved into either KiCad or FreePCB. I'm on KiCad and this probably would take less than an hour for a non-KiCad user. Make the move today and you won't miss using the Eagle, ever.And I also notice your first PCB at the top most is different from the rest, please make sure they are the same. Else they will $$$...All the newer AVR-0, AVRDA, AVRDB and even the AVRDD parts are less likely to be available from LCSC unfortunately, hence the 2500 pieces MOQ (this the reel format of the 8-SOIC).You can just use a 3-pin pogo pin UPDI interface (or even 2-pin as it only need GND and UPDI at minimum to program).