We frequently get asked, "How clean should the PCM connector be when installing a chip?" The answer is "Really clean!" However, there always seems to be some confusion as to what is really clean and what is too clean. Hopefully this will provide some insight.
When the PCM is manufactured, they are dipped in silicone in order to help seal the components and prevent moisture contamination and corrosion. When installing a chip, this layer of silicone needs to be removed in order for the chip to make a solid contact with the circuit board. Failure to adequately clean the PCM contacts can result in a no-start condition, stalling while driving, poor performance, and even damage to the PCM and/or the chip.
Okay... so we've established that the connector should be
really clean. How do we clean it? The best method, if you have one available, is a BRASS scrub brush (for example:
Brass Mini Brush #46630 by Hyde Tools at HardwareAndTools.com). This is the ideal tool for cleaning because it removes all the silicone and does not damage the board or any components and does not remove the tinning from the contacts.
In know that Scotch-Brite pads are included with the chips, but Scotch-Brite should ONLY be used for a light polish once all the silicone has been removed from the edge connector. This includes removing any silicone from
in between each finger on the connector. In the absence of a small scrub brush, a toothpick works really well for these areas. Once the silicone is removed, then you can use the Scotch-Brite.
After you are done cleaning, there shouldn't be ANY copper showing. The contacts should still have a fully silver hue. Visible copper is an indication that you've removed the tinning on the contacts and you are more susceptible to corrosion on the contacts which will compromise the connection.
Another thing to keep in mind is that most standard card edge connectors are designed to accept .062" to .064" thick circuit boards. As it happens, OBS computer PC Boards ('94-'97) are .062" thick so there is little concern regarding connection problems. However, '99 and later computers are only .050" thick and can present a significant connection problem, especially if you remove .001" to .002" of the tinning from the edge connector.
In the event that the contacts have been overly cleaned, it is not a lost cause. Any experienced electronics or TV repair shop should be able to re-tin the contacts which will help provide a better surface for the chip to grab on to and eliminate connection problems.
Here are a couple examples:
Before Soldering (click to enlarge):
After Soldering (click to enlarge):
Pay particular attention to the slightly raised contacts after soldering. They are smooth and slightly rounded and are about .008" thick. Counting both sides, this helps make up the difference in board thickness that the edge connectors are expecting. Also, if you look closely, you can still see specks of silicone still left in between each of the contacts. This was after using only a Scotch-Brite pad to clean the connector. (I couldn't find my scrub brush!) It obviously doesn't get all the silicone from between each finger in the contact. Again, a toothpick is excellent for removing these remnants.
Your local Ace hardware usually has the little brass brushes in the paint department for a buck or two. It is worth the investment if you happen to be by one. If not, then just take your time with the connector and carefully remove the silicone before going at it with the Scotch-Brite pad. A little patience here can save a lot of aggravation down the road.
Hope this helps.
