|Ask the Experts|
October 25, 2020
Initial Screen Print Test Board
Is it recommended to print one cycle before printing the first production board? I could use a scrap board or blank plastic card for the first print.
|Expert Panel Responses|
It is not a bad idea. It will depend much on the quality of the solder paste. Some pastes are ready to print right out of the jar/cartridge. Some need a few knead strokes to get them going.
Technical Support Engineer
This is a good practice in order to set your printer when you run a PCB for the first time. Once your printer parameters are set you shouldn't have to do a one cycle print before production. Always have your print inspected by an AOI system for quality of solder deposition in critical areas such as fine-pitch and micro-BGA's.
I'd also recommend to set the printer with a production PCB. Refrain from using blank plastic cards since they do not provide you with complete picture of your pad landscape.
Senior Manufacturing Engineer
The important issue is the accuracy of the alignment of the stencil to the board. If the printer does not have camera capability for alignment, then I would suggest running a test alignment board.
I would not run a plastic card, as it may not have the artwork on the card. I've seen people use a regular board and apply a removable film on the board, so the accuracy can be checked to the physical artwork. If it is aligned then the removable film can be removed and the process can be started.
If you do use a board, be it a scrap board or not, make sure to clean it properly to get all the solder paste off the board and out of the plated through holes.
Vice President, Technical Director
Yes. Good practice.
Vice President Technology
Yes it is a good idea to print 1 or two blank/scrap circuit boards before printing the first production board. This helps the solder paste to wet and flow properly through all of the stencil apertures.
This depends on the component sizes and paste deposition required. If you are placing any 0.4mm BGA's or 0201 components then I would recommended first board printing. This is purely because volume for these types of components are critical.
Typically, solder paste has air pockets and bad roll of the first print, you will find solder paste skips, voids which effects the total volume required on a pad. If you have an SPI, then I would low volume can be flagged, hence no need for first board printing even if you are using .4mm BGA's or 0201 components.
Process Engineering Manager - Electronics
Altech UEC, South Africa
Many modern pastes will print better if they are subjected to a kneed cycle (2 to 4 sweeps of the squeegee) prior to printing.
This process achieves two things one helps to condition the solder paste, optimising its rheology, wetting out the squeegees and making sure that the bead of paste is of even size across the squeegee and extends beyond the end of the apertures.
Two it ensures that the apertures of the stencil are fully wet out, this is important in determining the release of the paste from the stencil. One common solution to this problem is to perform a double sweep for the first print, this invariably produces a usable board with good print volumes.
Senior Applications Chemist
There are a couple reasons why it might be a good idea:
It depends on what is the population on the board. The smaller the parts/apertures, the higher risk of paste deposit deficiencies. This is not necessary, however it is not a bad idea if you can do that.
Engineering and Operations Management
The experts seem to be unanimous, and I agree it is a good idea. Not only for the reasons stated, but if you have ever cleaned a stencil you know that the flux residue on the surface of the stencil is very sticky, and this is what helps the paste to "roll" properly. You may need one or two passes to obtain that flux residue before the paste begins printing properly without sliding in a pile.
|Submit A Comment|
Free Newsletter Subscription
Circuitnet is built for professionals who bear the responsibility of looking ahead, imagining the future, and preparing for it.
Insert Your Email Address