Thanks! Feel free to post this as a shareable project on Seeed! I have no plans to turn it into a product. It was designed with a non-profit freemium trial license of Eagle (for 4-layer board support), and I just wanted to share it with the community. I'm already busy enough with making my programmable ROM SIMMs, so I wouldn't have time to mess with selling these anyway
Beware: SIMMs need to have 1.2 mm thickness. I'm not sure that OSH will do that thickness (typical PCB thickness is 1.6mm), so Seeed is probably the better route anyway. I totally understand what you're saying about not wanting to destroy DEC RAM. I will be interested in hearing the price you get back for the parts quote! I highly doubt you will be able to get the price of a SIMM down to $5. Even simple boards are pretty expensive to have assembled. My rough guess (assuming parts can be found) is that a full fab+assembly quote would be somewhere on the order of $20-$30 per board in quantities of 100. I'd be very curious what you see for quotes...let me know just for future reference if you don't mind!
Yeah, you're probably right about the assembly costs; this is my dayjob too, but I've seen some proto assembly houses do cheap assembly for a low-item-count BOM (2 line items, 16 parts total isn't too bad). No guarantee, and I don't know what Seeed's assembly cost is (didn't quote that yet). I'm also not opposed to hand-assembling them in batches; I have a hot air station that I've used to great effect on similar projects, and I could always acquire another toaster oven (lost my old one in a move a while back and haven't needed it since).
I'm not looking to make a profit either, as long as I don't go broke, But I figure if I can make 120 SIMMs or so, that should cover at least 15 IIfx owners.
Oh wow, that's better than I was expecting. I did a quote for my 8 MB ROM SIMMs on CircuitHub and it was looking like $22-ish each for 100. That included parts, PCBs, and all setup fees though. Plus those chips are fine-pitch.
Edit: FWIW, my $20-30 thought above included the parts and PCBs...
It really depends on your assembly house. The prices bigmessowires quoted above sound typical for high-volume, long-lead assembly in China, but you might have a hard time getting prices like that in small quantities, especially here in the US. Do you have a house you work with that might provide that? (Edit: Boy, I should learn to read. You pointed it out in the original post)
Ancillary question: is there reason to believe that the IIfx actually makes use of the individual bit write control lines? The 68030 certainly can't do anything with that, though it's unclear whether the board chipsets can make use of it. I ask because the quote I got back from the surplus dealer was absurd ($5 each for ancient chips they've got 60,000 of, no thanks), and 16Mx1 chips are hard to find on eBay (there are 3 reels of 72x KM41C16000CK for $60 each, which is less than a buck each, at least), but if we can use x4 chips, it might make the search a bit easier. 60ns chips aren't that hard to find, either, which would give us some timing margin for a 2-to-4 decoder to make a composite board if need be to use 4MxN chips.
I could imagine the bit-level write controls being used in the LaserWriter IINTX, which is the only other machine I remember using this RAM.
Edit 2: Of course, I've never seen an x4 DRAM that had separate D and Q lines, which is perhaps the core purpose of the 64-pin SIMMs. Oh well.
Nice! I bet you could negotiate your way to a 50% discount there, if you bought at least a few hundred.
I've never used Smart-Prototyping (the assembly place that I linked), although I almost did. I went through the whole process of sending them my design files, and getting a quote. They seemed pretty helpful, but the turn-around time on emails from the United States was slow due to the time difference, and there were some occasional small misunderstandings. There's a minimum order value of $100 for the pricing I quoted, but no specific minimum quantity of units. I think they would be fine, if you're willing to invest some time upfront in a marathon-length email exchange to arrange the details.
I ended up selecting this place in San Jose, CA instead: http://msdus.com They quoted me a single price for parts, assembly, and testing, so I don't know exactly how many cents per pad they charge or if they even calculate it that way. The total price was around 20% more than with Smart Prototyping, but I decided the value of working with a local company was worth it. I'm about 30 miles from San Jose, so I drive there to pick up finished boards in person and talk with the owner about possible changes and improvements. My first order with them was for 50 units with a cost around $1400 as I recall. If your boards are simple and cheap, they will probably want a larger number of units so there's enough profit to make it worth their time. It usually takes about six weeks from when I request a new batch of hardware, to when it's finished. I'm sure they could do it faster if I paid more, but six weeks is fine with me as long as I plan ahead.
If anyone knows of other good low-volume assembly services, I would love to hear about them!
I've been very happy with Advanced Assembly (aapcb.com). They're quick, accurate, and great for prototype assembly (parts can be in bags or cut tape, boards don't need to be panelized, etc.). Not cheap, though. I don't think I'd use them for this.
Most assembly houses I've worked with price generally based on the part count, line item count and to some extent the part type. These days, high-end assembly houses don't charge much of a premium for BGAs or other leadless parts for proto quantities, though they'll start to at volume (because the yield typically goes down). I don't see per-pad pricing very much, but I don't work a lot with Chinese houses, and when I do we just send it out for quote and they don't itemize their pricing breakdown.
The charts on the link you sent do break down the optimum price for various volumes and techniques; looks like manual assembly generally wins with very small quantities, but once you hit 100, automatic wins (sounds about right to me). Most places will make their own stencils, and it looks like they probably will too, but it's not clear how much that costs (can be from $30-$200, depending). It's also not clear whether they want the boards panelized, but it looks like Seeed will do that.
There are also lots of Chinese houses that will do both the PCB and the assembly for you, which can save cost and time; you just send them the parts, gerbers and fab/assembly drawings. These aren't exceptionally complex boards, so that might be a reasonable approach as well. I might see about quoting it out to a few places I've used if I can actually get a more favorable price on the RAM. I'm not expecting a 50% discount, but it would be nice if I could get under $1 a chip.
The other thing is: testing. Doug, where did you get your 64-pin ROM SIMM sockets for your programmers? I'm having a hell of a time trying to find 64-pin SIMM sockets anywhere. Is it the same socket as the ROM SIMM?
Yeah, the IIfx actually uses the separate D and Q pins. (I doubt it needs to have the eight separate WE pins, but by looking at the pinout it's clear that it was designed to use eight x1 chips). The 68030 itself doesn't need the pins to be separate, but my understanding from what I've seen trag post is that it allows the IIfx to go and do something else while the memory controller is still busy finishing a write to RAM.
trag actually figured out how to add some extra logic to allow 4-bit chips to be used on his SIMMs, but he found that they didn't work in certain combinations. It's kind of weird. With all of the stuff he struggled with, I decided that it's just not worth going for anything other than 1-bit chips. He summarized his research here:
$5 each is crazy...that aliexpress link looks a lot better! Honestly that's why I went to salvaging the chips off of DEC RAM...it was just too expensive any other way. I hadn't seen the aliexpress source at that point though.
Thanks for sharing your guys' assembly places! I've been interested in figuring out at what point it becomes feasible for me to do it that way instead of wasting weekends assembling boards (and breathing solder flux fumes).
I'm fairly sure that for boards as small as SIMMs, most places would end up doing them panelized. The pick and place machines will want a larger board that would contain a bunch of SIMMs on them.
The 64-pin SIMM socket is something I struggled with too. Yes, it's the exact same socket that they use for the ROM SIMM. The first ones I bought came from a guy on 68kmla who found a bunch of them at his local parts place. When I ran out recently, I started doing some searching and discovered the part number is: Tyco 822021-2. They are long out of production, but I've found a few suppliers on the first page of Google. I got a bunch from "NTI - The Connector People." They're friendly and I'm not worried about finding parts for my programmers anymore. The main problem for someone who only needs a few is that these places have minimum order quantities. If you only need one or two I'd be happy to send some your way...
Yeah, I knew about the separate D and Q pins; it cuts down on bus turnaround time. They're basically doing with the Fast Memory Controller and the separate D and Q pins what SDRAM does internally. It's pretty neat! Bummer it didn't really catch on.
Anyway, I had found the part number, but hadn't found anywhere that would sell it. I'll check NTI. I'm not so worried about an MOQ; I'll need plenty to build up a decent test jig, because those slots don't last forever.
I have some quotes out for parts vendors on regular Alibaba as well; that may well be a lot cheaper.
Got one quote from a regular Alibaba vendor for $1.55/pc, and they have 639 of them. Waiting for more. At that rate, you're talking about more than $10/SIMM just for parts, but it's still considerably better than what I see these days even for 4 meg ones.
Oh, and Doug: Just as a note, Advanced Assembly will work on boards considerably smaller than SIMMs without them being panelized. They did my wireless sensor nodes (1.5" square, populated both sides) on bare PCBs, no additional charge. Not bad. Like you say, though, most assembly houses prefer them panelized, and Seeed doesn't seem to charge extra for that.
Welp. I bought it. After various fees, it came to about $1.30 a chip, which puts the parts cost (not counting PCB) slightly above $10/SIMM. Now I gotta figure out how I'm going to get them built and sold at a reasonable cost...