How long can you leave paste - update

Yes, Hand Up here. I would think you would have a quality problem. I am assuming you're doing this process in some sort of batch mode.

I would hope that you can process your boards within a few minutes after components being placed. Things that I would worry about is fulx starting some sort of contamination on your leads and BGA's. My process state that the board must be placed in the oven within 30 minutes of printing. But, I am running an inline process that allows me that kind of control.

Worse case, I would say not to wait no more than an hour or two.

Really, the only truly correct way to figure this out in your eviourment is to run a DoE and see what happens. I would start out by printing a series of PCB's and process them at 45 minutes apart.

reply »

Please tell us you are not making any function critical items like pace makers or aircraft navigation equipment.

reply »

Hi Chris,

Yes, my hand is up. But the problem is WHY you are stock piling printed boards. Is it a single printer used to feed various lines? I would think that since you are hand placing parts, that this printer would be able to keep up. Obviously if your solder joints meet your needs, there isn't a over-driving problem. If you are looking for a cheap means to just get better, you may want to look and a manual or hand solder platform. They do work well and could probably keep up with your hand placing of parts. The same operator that places parts can manually screen print the board first. Just an idea for you to kick around.

reply »

Hand up here too. While most pastes have some flexibility and you may get by without too many problems, I don't think any of them are designed with long wait times in mind.

What I'm confused about is what your operator is doing when boards ARE running on the machine. Does he/she have time to do the hand-adds while machine processing (what we do) or is the hand add process the bottleneck?

reply »

OK - going to set up some measurements so we can see how big this problem is. I've got the following so far...

Number of boards pasted per employee per shift Number of hand placed parts per employee per shift Number of people per shift Time pasting machine is utilised in a shift Time pick and place machines are utilised in a shift Time oven is utilised in a shift Time spent hand placing parts in a shift Machine down time per shift Number of hand placements per board Number of different boards per shift Number of boards in each batch Complexity of board Number of boards cleaned and repasted Time from pasting board to reflow oven Time board takes from start (picking up the job) to finish (on to next stage) Time taken to set up first board Time taken to place first component after pasting Time taken to place last component after pasting

... any more for any more?

reply »

Hello, simply downkload your solderpaste specification from the internet and look, u will find your desired answer. bye

reply »

Until it drys out but why would any reasonable person want that.

reply »